Printer Friendly

Oocyte maturation and fertilization in marine nemertean worms: using similar sorts of signaling pathways as in mammals, but often with differing results.

Abstract. In marine worms belonging to the phylum Nemertea, oocyte maturation and fertilization are regulated by the same general kinds of signals that control such processes in mammals. However, unlike mammalian oocytes that develop within follicles, nemertean oocytes characteristically lack a surrounding sheath of follicle cells and often respond differently to maturation-related cues than do mammalian oocytes. For example, elevators of cyclic adenosine monophosphate (cAMP) or cyclic guanosine monophosphate (cGMP) levels promote the resumption of meiotic maturation (=germinal vesicle breakdown, GVBD) in nemertean oocytes, whereas increasing intraoocytic cAMP and cGMP typically blocks GVBD in mammals. Similarly, AMP-activated kinase (AMPK) signaling keeps nemertean oocytes from maturing, but in mouse oocytes, AMPK activation triggers GVBD. In addition, protein kinase C (PKC) activity is required for seawater-induced GVBD in nemerteans, whereas some PKCs have been shown to inhibit GVBD in mammals. Furthermore, although fertilization causes both types of oocytes to reorganize their endoplasmic reticulum and generate calcium oscillations that can involve soluble sperm factor activity and inositol 1,45-trisphosphate signaling, some discrepancies in the spatiotemporal patterns and underlying mechanisms of fertilization are also evident in nemerteans versus mammals. Thus, to characterize differences and similarities in gamete biology more fully, aspects of oocyte maturation and fertilization in marine nemertean worms are reviewed and briefly compared with related findings that have been published for mammalian oocytes. In addition, possible causes of the alternative responses displayed by oocytes in these two animal groups are addressed.


For animals to develop normally. oocytes must resume meiotic maturation and undergo a process of nuclear disassembly, referred to as germinal vesicle breakdown (GVBD) (Voronina and Wessel. 2003). In most oocytes. GVBD occurs before fertilization and is required for proper activation by sperm (Whitaker and Swann, 1993; Stricker. 1999; Runft et al., 2002). Given the fundamental roles played by oocyte maturation and fertilization, it is not surprising that a database search for such topics can yield over one hundred thousand references. The majority of these articles cover deuterostome animals (e.g., chordates and echinoderms) rather than protostomes (e.g., arthropods and molluscs), and most recent reviews of such topics have concentrated on the vast literature that has been compiled for mammals (e.g., Evans and Gadella, 2011; Kang and Han. 2011; Silvestre et al., 2011; Wakai et al., 2011; Yamada and Isaji, 2011; Ito and Kashiwazaki, 2012; Miao and Williams, 2012; Nogueira et al., 2012; Sobinoff et al., 2012; Swann and Lai, 2013).

In addition to various studies of mammals, aspects of gamete biology have also been examined in such marine invertebrates as jellyfish. annelids, molluscs, echinoderms, and ascidians, owing in part to the ease with which eggs and sperm can be obtained (e.g., Deguchi et al., 1996, 2005; Yi et al., 2002; Chausson et al., 2004; Dupont and Dumollard, 2004; Takeda et al., 2006; Deguchi, 2007; Lambert, 2008; Vacquier, 2011; McDougall et al., 2012; Santella et al., 2012). However, in spite of their benefits, commonly used marine invertebrate oocytes may also present some drawbacks. For example, jellyfish and sea urchin eggs complete meiosis in the ovary (Freeman and Ridgway, 1988: Wessel et al., 2002; Miyata et al., 2006), which can complicate analyses of prophase-I arrest and meiotic resumption. Similarly, the solitary calcium wave generated at fertilization in starfish and sea urchins (Stricker et al., 1992; Stricker, 1995) differs from repetitive calcium transients in other oocytes such as those of mammals, which, unlike starfish oocytes and sea urchin eggs, are fertilized at a metaphase-arrest point during maturation (Jones, 1998; Sardet et al., 1998; Stricker, 1999; Swann and Yu, 2008).

Thus, to assess alternative types of oocytesu1/4 analyses began to be conducted about 15 years ago on marine nemertean worms, which are sometimes confused with alike-sounding nematodes. However, nemerteans, or "ribbon worms," belong to their own phylum of about 1300 species in the lophotrochozoan clade of protostomes that includes molluscs and annelids, whereas nematodes and related invertebrates such as arthropods constitute separate phyla of ecdysozoan protostomes (Kajihara et al., 2008; Struck and Fisse 2008). Prior to the 1990s, much of what was known about nemertean oocytes was derived from classical studies (e.g., Coe, 1899, Wilson. 1900), and except in a few cases (e.g., Freeman, 1978; Jaffe et al., 1985), the mechanisms of oocyte maturation or fertilization in nemerteans had not been analyzed. However, more recent investigations have begun to show that nemerteans can utilize similar sorts of intraoocytic signaling pathways as in mammals, and yet, as reviewed further in the following sections, such pathways often mediate different responses in nemertean than in mammalian oocytes.

Materials and Methods

Ripe specimens of the nemerteans Cerebratulus sp., Emplectonema gracile (Stimpson, 1837), Micrura ala.skensis Coe, 1901, and Tubulanus polymorphus Renier, 1804 were collected at low tides on San Juan Island, Washington. USA. whereas C. lacteus (Leidy. 1851) adults were purchased from the Marine Biological Laboratory, Woods Hole, Massachusetts. Immature oocytes obtained from cut females were pre-incubated in ice-cold calcium-free seawater (CaFSW) (Schroeder and Stricker. 1983) for 1.5-2 h to reduce spontaneous GVBD. Dejellied oocytes were then transferred to seawater (SW), artificial seawater (ASW), or CaFSW and kept at ambient SW temperatures (-12-14 [degrees]C) with or without pharmacological modulators. Drug dosages were adopted on the basis of literature reports or dose-response curves that identified minimum effective concentrations. Western blots of total cell lysates were performed as described elsewhere (Stricker, 2011; Escalona and Stricker, 2013). Similarly, histological methods and confocal imaging of oocytes injected with probes for tracking endoplasmic reticulum (ER) dynamics, calcium ions, or cyclic adenosine monophosphate (cAMP) levels were carried out as detailed previously (Stricker, 1996; Stricker et al., 1998, 2001; Stricker and Whitaker, 1999; Stricker and Smythe, 2001). Nearly all images and graphs are comparable to previously published figures in cited papers, which provide full protocol descriptions. However, Figures 2E and 3A document some as-of-yet unreported data and are thus supplemented with methodological details in the figure legends. Given that mammalian gamete biology has been thoroughly described in recent reviews, coverage here of mammals is restricted to topics that can be directly compared to what has been reported for nemerteans.

Results and Discussion

Oogenesis and the production of follicle-free oocytes in nemerteans

In most marine nemerteans, sexes are separate, and ripe females spawn their oocytes prior to undergoing external fertilizations (Stricker, 1982, 1985, 1986, 1987; Stricker and Folsom, 1998) (Fig. 1A, B). Follicle cells are characteristically lacking during nemertean oogenesis, and in species such as Cerebratulus lacteus, Micrura alaskensis, and Par-borlasia corrugatus, numerous ovaries develop along the body, with each gonad producing dozens to hundreds of microlecithal oocytes that average 70-130 p.m in diameter (Stricker et al., 2001; Norenburg and Stricker, 2002; Grange et al., 2011). Thus, nemerteans can supply copious amounts of oocytes for analyses that are not subject to the potentially confounding effects of follicle cells (Fig. 1B-G).

Similarly, mammals are normally dioecious and generally produce oocytes similar in size to those of microlecithal nemertean specimens (Hartman, 1929). However, compared to most nemerteans, mammals ovulate fewer oocytes (Zuckerman, 1951) prior to internal fertilizations in the female reproductive tract. Moreover, unlike in nemerteans, mammalian oocytes develop in a follicle that can exhibit some species-specific differences (Griffin et al., 2006) but invariably promotes complex interactions between oocytes and their surrounding follicle cells (Matzuk et al., 2002; Rodrigues et al., 2008; Su et al., 2010; Gilchrist, 2011). In fully grown mammalian follicles, GVBD is prevented by inhibitory cues that are produced by the follicle itself. Maturation can then be triggered by the pituitary-derived gonadotropin, luteinizing hormone, and by signals of follicle cell origin, such as epidermal growth factor-like ligands (Park et al., 2004). Alternatively, after removal from their follicles, cumulus-enclosed or denuded oocytes of mammals are prevented from maturing by exogenously supplied GVBD antagonists. Compared to intact follicles, such preparations may provide more straightforward assessments of experimental results, but neither responds to the same spectrum of maturation-inducing cues that elicit GVBD in whole follicles (Downs, 2010).

Stimulation of nemertean GVBD by seawater or cAMP-elevating drugs vs. the blockage of GVBD by calcium-free seawater

At 10-14[degrees]C. fully grown nemertean oocytes can initiate GVBD within about 15-45 min after being stimulated by natural seawater (SW) (Stricker and Smythe, 2000). Conversely, nemertean oocytes remain immature with an intact germinal vesicle when treated with calcium-free seawater (CaFSW) (Fig. 2A-D), and such inhibition is not due to morbidity, since oocytes that are removed from CaFSW after a day of incubation are capable of undergoing normal maturation and fertilization (Stricker and Smythe, 2000).

The differential effects of SW versus CaFSW on GVBD are not solely mediated by calcium ions, given that CaFSW supplemented with 10 mmol [l.sup.-1] calcium such as found in SW elicits less GVBD than in SW controls (Stricker and Smythe, 2000). Moreover, treatments with calcium channel blockers and the calcium chelator BAPTA inhibit GVBD in calcium-containing artificial seawater (ASW) but fail to prevent GVBD in SW-stimulated oocytes (Stricker and Smythe, 2000). Furthermore, conditioning ASWs for several weeks with marine sediments transforms such solutions into as robust stimulators of GVBD as SW (Stricker and Smythe. 2000). Thus, SW apparently contains maturation-inducing substance(s) other than just calcium itself, and although such substances have yet to be identified, experiments using boiled SW or SW that had been fractionated by MW-cutoff filters suggest the presence in SW of maturation-inducing stimuli that are heat-stable and less than 30 kD (Fig. 2E). Accordingly, the molecular weight and apparent non-proteinaceous nature of active component or components in SW are at least consistent with some GVBD inducers identified for other oocytes, including maturation-inducing sterols (Byskov et al., 2002).

In addition to SW's stimulatory effects, cAMP-elevating drugs also trigger GVBD and can do so by alternative modes of action, given that nemertean oocytes mature in response to (1) 8-bromo cAMP (Fig. 2F); (2) the adenylate cyclase (AC) activator forskolin; (3) inhibitors of phosphodiesterases (PDEs), including the broadly acting PDE antagonist IBMX and other PDE blockers (etazolate, Ro-20-1724. and rolipram) that are more specific for type 4 PDEs; and (4) serotonin (=5HT), which may act as both an AC stimulator and a PDE inhibitor (Stricker and Smythe, 2001). Such drugs induce a marked pre-GVBD increase in intraoocytic cAMP at physiologically relevant doses (Fig. 2G) (Stricker and Smythe, 2001). Moreover, cAMP elevators cause maturation in calcium-free ASW and can trigger GVBD without markedly affecting intraoocytic calcium ion levels (Stricker and Smythe, 2000, 2001), collectively suggesting that cAMP-elevating drugs elicit GVBD Oct their shared ability to increase cAMP rather than by off-target effects, such as calcium-mediated signals. Owing to technical limitations of the experimental setup used for such microinjection and imaging analyses, it has yet to be determined if immature nemertean oocytes also generate either a cAMP or a calcium transient in response to SW stimulations. However, as discussed further in the following sections. several lines of evidence suggest that even if SW elicits such transients, the amplitudes or spatiotemporal properties of these signals do not fully mimic the intraoocytic responses mediated by exogenously applied cAMP elevators.

Protein kinase A (PKA) isotypes are fundamental mediators of cAMP signaling in cells (Taylor et al., 2004). Based on studies of mammalian follicles where dibutryl-cAMP (db-cAMP)-induced cAMP rises are thought to target type I PKAs, and 8-bromo-cAMF's actions are apparently associated with type H PICA signaling (Downs and Hunzicker-Dunn, 1995), the differing effectiveness of 8-bromoversus db-cAMP (Fig. 2F) in nemertean oocytes could indicate that a type II PKA mediates cAMP signaling. In any case, regardless of which specific PKA functions in nemertean oocytes. GVBD in response to cAMP elevators is blocked by PKA inhibitors (Sticker and Smythe, 2001). Accordingly, in blots probed with an antibody to sites phosphorylated by active PKAs, maturing oocytes display increased phosphorylations of several unidentified putative PKA targets, including a major band at about 130 kD, and such responses are reduced to varying degrees by the PKA blocker H89 in oocytes that had been stimulated by SW versus cAMP elevators (Stricker and Smythe, 2001, 2006A).

The alternative effects of H89 during SW versus cAMP stimulations suggest that cAMP signaling does not fully overlap the pathways that mediate SW-induced GVBD. This conclusion is also supported by the findings that (1) some oocyte batches respond fully to one, but not the other, kind of stimulation; (2) sensitivities to SW versus cAMP elevators decline at different rates during oocyte aging; and (3) as discussed further in the section "Inhibition of SW-induced GVBD in nemerteans by various pharmacological modulators ... ", other pharmacological modulators block SW-induced GVBD, whereas co-adding cAMP elevators along with those modulators restores GVBD (Stricker and Smythe, 2000; Stricker et al., 2010). In any event, although it remains unknown if oocytes in the field are initially stimulated by intraovarian cAMP signaling before spawning or if spawned oocytes begin to mature only after contacting SW, laboratory analyses reveal that nemertean oocytes can mature in response to either SW or cAMP elevators.

When compared to nemertean GVBD that can start as early as 15 min post-stimulation, the lag between maturation stimulation and GVBD onset is longer in mammals, even at the higher temperatures used for such oocytes. Thus, although GVBD timing varies widely among species and is affected by culture conditions, mammalian oocytes typically do not begin GVBD until 2-24 h post-stimulation (Hegele-Hartung et al., 1999; Lu et al., 2001; Fan and Sun, 2004).

Furthermore, as noted for nemertean oocytes, some studies of mammals have also indicated that GVBD does not require intraoocytic calcium transients (Paleas and Powers, 1981; Carroll and Swami. 1992; Tombes et al., 1992; Mehlmann et al., 2006). However, other analyses have shown that mammalian GVBD is calcium-dependent (Homa, 1995; Su et al., 1999; Tosti, 2006) and that external calcium influx can play an important role in meiotic resumption (Bae and Channing, 1985; Goren et al., 1990; Zhou and Jin, 2007). Such conflicting results could be due to species-specific differences or to variations in experimental procedures such as the type of maturation inducer that is used and whether or not oocytes are associated with follicle cells (Homa, 1995; Fan et al., 2004).

By contrast, a well-unified literature has demonstrated that prolonged elevations in intraoocytic cAMP prevent GVBD in mammalian oocytes and that meiotic resumption is associated with a decrease in intraoocytic cAMP (Mehlmann, 2005; Downs, 2010; Jaffe and Norris, 2010; Sole et al., 2010; Tripathi et al., 2010; Tsafriri and Dekel, 2010). Accordingly. intraoocytic PKA inhibits GVBD in mammals, whereas the relief of PKA's effects in response to decreased cAMP levels promotes GVBD (Kovo et al., 2006; Zhang et al., 2008; Pirino et al., 2009; Oh et al., 2010). Alternatively, in a few cases, mammalian GVBD has been shown to involve an initial transient increase in intraoocytic cAMP (Salustri et al., 1985; Yoshimura et al., 1992; Mattioli et al., 1994), and pulsed applications of cAMP elevators can trigger maturation (Chen et al., 2009). Nevertheless, the generally inhibitory effects of intraoocytic cAMP/PKA on GVBD in mammals differ from the stimulatory actions of cAMP signaling in nemerteans and other marine invertebrates that undergo cAMP-induced GVBD (Deguchi et al., 2011).

Roles of maturation-promoting factor, mitogen-activated protein kinases, and protein neosynthesis during nemertean GVBD

Two key cell cycle regulators in eggs are maturation-promoting factor (MPF) and mitogen-activated protein kinase (MAPK) subtypes, called extracellular signal regulated kinases 1/2 (=ERK1/2, "MAPKs 3/1," or hereafter, simply MAPKs) (Kishimoto, 2003; Sun et al., 2009). In nemerteans, MPF is activated before GVBD, and such activation does not appear to depend on the neosynthesis of MPF's regulatory subunit, cyclin B, given that cyclin B1 is present in immature oocytes and does not markedly increase before GVBD (Fig. 3A). Moreover, although such results do not preclude the possibility that an alternative isoform of cyclin affects MPF activity, protein neosynthesis in general appears to be nonessential for nemertean oocyte maturation, since several protein synthesis inhibitors fail to block GVBD (Stricker and Smythe, 2000; Smythe and Stricker, 2005). Alternatively, MPF apparently involves phosphorylation changes in MPF's kinase moiety (=Cdc2 or Cdk1), as maturing oocytes exhibit both decreased inhibitory phosphorylation at the Y15 site of Cdc2 and increased stimulatory phosphorylation at T161 on Cdc2 (Stricker and Smythe, 2003, 2006a) (Fig. 3B). Furthermore, MPF activation is necessary for GVBD, given that MPF inhibitors consistently block GVBD, although, for undetermined reasons, higher doses of MPF antagonists are needed to inhibit GVBD in oocytes that are stimulated by cAMP elevators versus SW (Fig. 3C) (Stricker and Smythe, 2003. 2006a).

As is the case with MPF, MAPK is activated before GVBD (Smythe and Stricker, 2005; Stricker and Smythe, 2003, 2006a). However, oocytes incubated with the MAPK kinase (MAPKK) inhibitors CI1040 (ci) and PD98059 still complete GVBD without marked MAPK activity (Smythe and Stricker, 2005; Snicker and Smythe, 2006a; Stricker, 2009b) (Fig. 3B). Moreover, although some oocyte batches fail to mature in SW solutions of the MAPKK inhibitor U0126 (uo) (Smythe and Stricker, 2005), such inhibition is apparently due to off-target effects rather than to MAPK deactivation per se. This conclusion is based on the findings that co-adding cAMP elevators along with uo restores GVBD without activating MAPK and that combining uo with ci prevents the onset of GVBD that normally occurs when ci alone is used to deactivate MAPK (Fig. 3B) (Stricker. 2009a. 2011).

As noted for nemerteans, mammalian GVBD typically involves changes in Cdc2 phosphorylations that convert inactive pre-MPF into active MPF (Choi et al., 1991: Kishimoto, 2003; Jones, 2004). Thus, MPF activation in nemerteans and mammals contrasts with the de novo synthesis of cyclin that activates MPF either in fish and non-Xenopus amphibians that lack pre-MPF (Yamashita, 2000: Suwa and Yamashita, 2007) or in Xenopus, where cyclin neosynthesis during progesterone stimulation can help to transform pre-MPF into MPF (Gaffre et al., 2011). Moreover, contrary to the view that the cyclin-dependent kinase activating kinase (CAK) responsible for phosphorylating 1161 of MPF is constitutively active throughout maturation of Xenopus oocytes and is thus not involved in regulating MPF activity during GVBD (Brown et al., 1994), T161 phosphorylation increases in maturing pig oocytes (Fujii et al., 2011), as has also been noted for nemertean oocytes.

As opposed to its pre-GVBD onset in nemerteans, MAPK activation can

occur either before or after GVBD in mammals (Fan and Sun, 2004; Liang et al., 2007; Sun et al., 2009). Nevertheless, regardless of the timing of MAPK activation, most studies indicate that intraoocytic ERK MAPK activity is not required for mammalian GVBD (Sun et al., 2009). Conversely, such activation must occur in mammalian follicle cells for GVBD to proceed (Fan et al., 2009), and active ERK MAPK is needed within post-GVBD oocytes of mammals for the successful completion of meiosis (Fan and Sun, 2004; Liang et al., 2007; Sun et al., 2009).

Unlike in nemerteans, in ungulate mammals protein synthesis inhibitors block GVBD (Fulka et al., 1986; Kastrop et al., 1991; LeGal et al., 1992; Alm and Hinrichs, 1996). Conversely, such treatments fail to prevent GVBD in rodents (Schultz and Wassarman, 1977; Fulka et al., 1986; Plancha and Albertini, 1992). Aside from species-specific differences, such varying responses may depend on the timing of inhibitor application or on the presence versus absence of follicle cells (Ekholm and Magnusson, 1979; Motlik et al., 1989).

Inhibitory effects of AMP-activated kinase signaling on SW-induced GVBD in nemerteans

In addition to modulating energy states (Hardie, 2007), AMP-activated kinases (AMPKs) can also regulate cell cycling (Alessi et al., 2006; Motoshima et al., 2006). Accordingly, blots probed with antibodies to active AMPK, inactive AMPK, or a phosphorylated substrate of active AMPK indicate that AMPK is active in prophase-arrested nemertean oocytes and deactivated during GVBD stimulated by SW or cAMP elevators (Fig. 4A) (Stricker et al., 2010a, b). Similarly, various AMPK agonists, including the AMPK mimetic AICAR, block AMPK deactivation and prevent SW-induced GVBD in nemerteans, whereas co-adding cAMP elevators overrides such blockage and restores GVBD (Fig. 4B-D). Moreover, AMPK activation in immature oocytes apparently downregulates two MPF stimulators--target of rapamycin (TOR) and nitric oxide synthase (NOS) (Stricker, 2011, 2012)--while upregulating the MPF inhibitor p27 Kip1 (Stricker, 2011), collectively indicating that AMPK signaling serves to inhibit GVBD in nemerteans (Stricker et al., 2010a, b; Stricker, 2011).

Conversely, intraoocytic AMPK is a potent trigger of GVBD in mice (Downs et al., 2002; Chen et al., 2006; LaRosa and Downs, 2006, 2007; Chen and Downs, 2008), and to a lesser degree, in rats (Downs, 2011). Alternatively, AMPK agonists block GVBD in cumulus-enclosed cow and pig oocytes (Bilodeau-Goeseels et al., 2007; Mayes et al., 2007; Tosca et al., 2007), although such inhibition is apparently due either to AMPK's actions on follicle cells rather than on the oocyte itself, or to ectopic effects on AMPK-independent pathways (Mayes et al., 2007; Tosca et al., 2007; Bilodeau-Goeseels et al., 2011). Moreover, although numerous studies have analyzed the effects of NO-related pathways on mammalian GVBD. potential interactions between intraoocytic AMPK levels and either NOS or TOR signaling have apparently not been reported for mammals.

Inhibition of SW-induced GVBD in nemerteans by various pharmacological modulators, and the overriding of such blockage by co-addition of cAMP elevators

As noted for AMPK activators, other drugs also block SW-induced GVBD in nemerteans, whereas such blockage is readily reversed by co-adding a cAMP elevator. For example, GVBD is prevented during stimulation in SW--but not in the presence of cAMP-elevators--following treatments of nemertean oocytes with blockers of Raf1, protein tyrosine kinases (Fig. 5A, B), protein tyrosine phosphatases, and the dual-specificity phosphatase Cdc25 (Stricker and Smythe, 2006a, b; Stricker et al., 2010a).

Similarly, SW-induced GVBD is inhibited by broad-spectrum protein kinase C (PKC) blockers and by more specific inhibitors of the calcium- and diacylglycerol-independent atypical PKCs (aPKCs) (Stricker, 2009a, b). Conversely, combining cAMP elevators with these PKC inhibitors restores GVBD (Stricker, 2009a, b) (Fig. 5C, D). Accordingly, blots also indicate that aPKCs, rather than conventional or novel PKCs, are activated during nemertean GVBD, and that the blockage of PKC activity induced by broad-spectrum PKC inhibitors is restored by co-adding cAMP-elevating drugs (Stricker, 2009a).

In addition, antioxidants and other commonly used antagonists of nitric oxide (NO)/cGMP signaling, including NOS inhibitors, a NO scavenger, and soluble guanylate cyclase (sGC) blockers, prevent GVBD induced by SW, but not by cAMP elevators (Stricker, 2012) (Fig. 5E-H). Moreover, NOS activity normally induced by SW stimulation is blocked by the AMPK activator AICAR, whereas co-addition of cAMP elevators reverses such blockage while restoring GVBD (Stricker, 2012).

One interpretation of these results is that SW and cAMP elevators trigger a single signaling cascade and that all of the tested inhibitors simply disrupt steps upstream to a cAMP rise. However, a solitary GVBD-promoting cascade is difficult to reconcile with the fact that some of the drugs exhibiting differential effects on SW versus cAMP-induced GVBD alter targets downstream to cAMP such as PKA, the PKA substrate Cdc25, or even MPF itself (Fig. 3C). Instead, then, these findings along with other data suggest that nemertean GVBD can be elicited by multiple signaling pathways (Stricker and Smythe, 2000, 2001, 2006a, b) and that, compared to GVBD triggered by cAMP elevators, SW-induced GVBD may be more dependent upon Raf1, tyrosine kinases, protein tyrosine phosphatases, Cdc25, atypical PKCs, NO or cGMP signaling. Regardless of how such differential drug effects are interpreted, the ability of cAMP elevators to restore maturation provides a means of confirming that GVBD blockages by drugs in SW alone are not simply due to oocyte morbidity.

Several studies have suggested that, as proposed for nemerteans, multiple signaling cascades mediate mammalian GVBD (Faerge et al., 2001; Lu et al., 2001; Zhang et al., 2005). However, some of the support for this view comes from comparing denuded oocytes to cumulus-enclosed ones and may reflect the effects of a "cAMP paradox" (Tsafriri and Dekel, 2010), wherein signaling cascades in mammalian follicles allow cAMP-elevating pathways in follicle cells to promote GVBD, whereas intraoocytic cAMP elevations serve an opposite, inhibitory role (Tsafriri et al., 1972; Dekel et al., 1988; Xia et al., 1994; Tsafriri et al., 1996). In any case, there appears to be no wide-ranging collection of modulators that can block or not block mammalian GVBD, simply depending on the presence or absence of cAMP elevators. Moreover, most pharmacological analyses of rodent oocytes indicate that inhibiting intraoocytic PKC promotes GVBD, and that, unlike the stimulatory aPKCs of nemertean oocytes, conventional PKCs block mammalian GVBD (Bornslaeger et al., 1986; Alexandre and Mulnard, 1988; Lefevre et al., 1992; Luria et al., 2000; Downs et al., 2001; Lu et al., 2001; Quan et al., 2003; Fan et al.. 2004; Denys et al., 2007). Similarly, although conflicting data have been reported for mammalian species, several studies of rat oocytes show that, unlike in nemerteans, NO/cGMP blocks GVBD (Nakamura et al., 2002; Yamagata et al., 2002; Sela-Abramovich et al., 2008; Tripathi et al., 2009).

Post-GVBD processes induced by fertilization in nemerteans

After GVBD, nemertean oocytes normally arrest at metaphase I by about 60-90 min post-stimulation. Fertilization of metaphase-I oocytes is followed by sperm incorporation, pronuclear reorganization, polar body production, and cleavage by about 2-6 h post-insemination (Stricker, 1987) (Fig. 6A). In the presence of PKC or MAPK inhibitors, polar body formation continues, whereas such antagonists usually block cleavage (Stricker, 2009b). Moreover, although inhibitors of phospholipase C (PLC) and Src-family kinases (SFKs) fail to block GVBD, both types of inhibitors prevent polar body formation and cleavage (Stricker et al., 2010c). However, such blockages apparently occur via alternative mechanisms, since the SFK antagonist PP2 promotes polyspermy (Fig. 6B) while disrupting pronuclear decondensation, whereas the PLC blocker U73122 (U7) reduces sperm incorporations and pronuclear migrations (Stricker et al., 2010c). Moreover, U7 prevents fertilization-induced calcium oscillations (see next section), whereas repetitive calcium transients continue to occur during fertilizations in the presence of PP2 (Stricker et al., 2010c).

Unlike those in nemerteans, mammalian oocytes characteristically arrest at metaphase II before fertilization, and even at the higher culture temperatures used for mammals, cleavage onset occurs later than in nemerteans. Thus, mice begin cleaving at about 25 h (Edwards and Gates, 1959) or about 17.5 h (Kaufman, 1973) post-fertilization during in vivo or in vitro treatments, respectively. Similarly, rat zygotes can take 21-23 h to cleave (Shalgi et al., 1985). Moreover, mammalian oocytes differ from those of nemerteans in that MAPK or PKC inhibitors can prevent polar body formation (Gallicano et al., 1993; Quan et al., 2003). Conversely, mammalian oocytes treated with PLC or SFK antagonists exhibit defects in sperm incorporations, pronuclear reorganizations, and cleavage that resemble what has been reported for nemerteans, and some of these defects appear to be associated with abnormal calcium signals (Dupont et al., 1996; Talmor-Cohen et al., 2004; Meng et al., 2006; McGinnis et al., 2011).

Fertilization-induced calcium dynamics

In all animals examined, fertilizing sperm cause the levels of intracellular free calcium ions in eggs to rise (Stricker, 1999; Miyazaki, 2006). Accordingly, fertilization of metaphase-I-arrested nemertean oocytes generates repetitive calcium increases that begin with a more-or-less simultaneous rise, or "cortical flash" (Parrington et al., 2007), around the oocyte perimeter (Fig. 7A, B) (Stricker, 1996, 1997, 2000, 2004; Stricker et al., 1998, 2010c; Stricker and Smythe, 2003). Several lines of evidence indicate that the cortical flash involves calcium influx, helps to prevent polyspermy, and depends on proper SFK signaling (Stricker, 1996; Stricker et al., 2010c).

Within 5-10 min after cortical flash production, each nemertean zygote begins to generate a series of calcium waves that travel about 10-15 [micro]m/s. Such calcium oscillations typically arise every 2-8 min for 20-60 min post-fertilization and end before polar body formation is completed (Stricker, 1996). Thus, pronuclei, which are generated only after polar bodies are fully formed, do not appear to play a vital role in terminating the calcium signal in nemerteans, unlike in some mammalian oocytes where pronuclear formation is involved in the cessation of calcium oscillations (Marangos et al., 2003).

In C. lacteus (Stricker, 1996), the initial one to three calcium waves arise from the site of sperm entry and fail to spread across the entire ooplasm, thereby resembling incompletely propagating transients in ascidians (Yoshida et al., 1998), or what have been called "tango waves" in computer models of calcium wave propagations (Li, 2003). Thereafter, calcium transients spread across the entire ooplasm as point-source waves and usually attain lower amplitudes than are exhibited by the calcium waves of mammalian fertilizations (Stricker, 1999). In addition, even if a sperm enters the animal hemisphere of the nemertean oocyte, later waves shift vegetally toward a repeated onset site (Stricker, 1996) (Fig. 7C, D) resembling the "vegetal pacemaker" in oocytes of other animals (Dumollard et al., 2002).

Since repetitive calcium transients continue to be generated in nemertean oocytes that are transferred to CaFSW after fertilizations in SW (Stricker, 1996), internal calcium sources mediating calcium signaling have been analyzed. Such studies reveal that [IP.sub.3]-sensitive stores are present and required for calcium signaling, on the basis of the findings that photoactivations of caged [IP.sub.3] cause calcium transients in unfertilized oocytes and that heparin injections to block [IP.sub.3]-mediated calcium release prevent fertilization-induced calcium oscillations (Stricker, 1996).

Given that immature nemertean oocytes fail to generate an oscillatory calcium response upon insemination (Fig. 7E) (Stricker, 1996; Stricker and Smythe, 2003), the possible effects of the maturation-associated kinases MPF and MAPK on calcium signaling have been examined. In such tests. MAPK kinase inhibitors eliminate ERK 1/2 MAPK activation but fail to prevent fertilization-induced calcium oscillations (Fig. 7F) (Stricker and Smythe, 2003). Conversely, the MPF inhibitor roscovitine either blocks repetitive calcium waves if used on mature oocytes before fertilization (Fig. 7G) or dampens existing oscillations if added after the onset of a fertilization-induced calcium response (Stricker and Smythe, 2003). Accordingly, treatments with colchicine to maintain MPF activity prolong oscillations during fertilization (Fig. 7H), collectively indicating that fertilization-induced calcium signaling in nemerteans depends on MPF, rather than MAPK, activity (Sticker and Smythe, 2003).

As noted for nemerteans, fertilization of mammalian eggs triggers calcium oscillations (Jones, 2007; Ducibella and Fissore. 2008: Swarm and Yu, 2008; Whitaker. 2006; Wakai et al., 2011). However, as opposed to what occurs in nemerteans, the first fertilization-induced calcium transient in rodents spreads as a point-source wave rather than a distinct cortical flash (Deguchi et al., 2000). In addition, subsequent transients in mammals can continue for a few hours after second polar body formation (Jones et al., 1995) and thus, unlike the short-lived oscillations of nemerteans, may persist for more than 20 h (Wakai et al., 2011). Moreover, oscillation intervals can be as little as 3 min or up to 50 min in mice versus cows, respectively (Bedford et al., 2006), and some of the later calcium transients in mammals propagate via a non-wavelike mode (Miyazaki et al., 1993) that has yet to be observed in oscillating nemertean oocytes. Furthermore, although the initial calcium oscillations during mammalian fertilization persist in calcium-free medium as noted for nemerteans, later oscillations require external calcium influx (Sardet et al., 1998). Also, MAPK-mediated alterations in [IP.sub.3] receptor sensitivity can play a key role in mammalian oocytes (Lee et al., 2006: Ito et al., 2008; Wakai et al., 2011), whereas in nemerteans, blocking MAPK activity does not markedly affect calcium responses.

Evidence for a soluble sperm factor mediating calcium oscillations at fertilization

In the nemertean C. lacteus, injecting whole sperm or sperm extracts into metaphase-I-arrested oocytes generates fertilization-like calcium oscillations (Stricker, 1996, 1997) (Fig. 8A. B). Similarly, injections of porcine sperm extracts can also produce calcium oscillations (Stricker et al., 2000). These findings indicate that the calcium response of nemertean oocytes is not dependent upon an external oolemmal receptor; instead, they are consistent with the view that sperm introduce a soluble oscillogenic factor into the ooplasm, as has been documented for other marine invertebrates, such as ascidians (Kyozuka et al., 1998; McDougall et al., 2000; Runft and Jaffe, 2000; Levasseur et al., 2007). Although the ability of porcine sperm extracts to trigger oscillations in nemertean oocytes suggests shared features in sperm factor signaling, the putative sperm factor of nemerteans remains uncharacterized other than that its oscillogenic activity is heat labile and contained in fractions of 10 to 100 kD (Stricker, 1997). Thus, it has yet to be determined if a sperm factor in nemerteans resembles what has been reported for mammals or any other animal in which sperm factor composition or function has been assessed (Coward et al., 2005, 2011; Harada et al., 2007, 2011; Wu et al., 2007; Aarabi et al., 2010).

As reviewed in detail elsewhere (Ito et al., 2011; Wakai et al., 2011; Nomikos et al., 2012; Swann and Lai, 2013), fertilization in mammals involves a soluble sperm factor. Several lines of evidence indicate that the sperm-derived oscillogenic factor of mammals corresponds to a sperm-specific PLC isotype, called PLC[zeta] (Heytens et al., 2009; Kashir et al., 2010, 2012; Ramadan et al., 2012), although not all findings support this view (Aarabi et al., 2012). In mice, sequestration of PLC[zeta] into nascent pronuclei is thought to function in terminating oscillations (Larman et al., 2004; Yoda et al., 2004). However, even though the PLC[xi]s of other mammals contain a nuclear localization signal, such isotypes fail to translocate into pronuclei and thus argue against nuclear sequestration of PLC[zeta] being the sole mechanism of terminating oscillations (Cooney et al., 2010).

Structural reorganizations of the endoplasmic reticulum during oocyte maturation and fertilization

As a result of the interrelated findings that immature nemertean oocytes fail to generate a robust fertilization-induced calcium response (Fig. 7D) and that the endoplasmic reticulum (ER) is the major mobilizable store of calcium during fertilization (Eisen and Reynolds, 1985), morphological changes in the ER have been assessed. Maturing nemertean oocytes that had been injected with the vital ER-specific probe DiI were examined with confocal microscopy (Teraski and Jaffe, 2004). Such analyses reveal that prophase-arrested nemertean oocytes possess a relatively homogeneous ER (Fig. 9A), except for scattered DiI-positive strands that may correspond to annulate lamellae-containing subcompartments of the ER (Beckhelling et al., 2003).

However, in metaphase-arrested nemertean oocytes, the ER is reorganized into microdomains, or "clusters," of about 5 pm in diameter (Fig. 9B, C), in both the animal and vegetal hemispheres, albeit without displaying any overt animal-vegetal heterogeneity that might correspond to the vegetal pacemaker activity observed during fertilization (Stricker et al., 1998; Stricker and Smythe, 2003; Stricker, 2006). After insemination, such clusters disassemble at about 20-60 min post-fertilization, which in turn precedes second polar body formation and corresponds to the cessation of oscillations (Fig. 9C) (Stricker et al., 1998; Stricker and Smythe, 2003). Inhibition of ERK-type MAPK activation fails to affect ER reorganizations (Stricker and Smythe, 2003). Alternatively, the MPF inhibitor roscovitine promotes both ER disassembly in unfertilized specimens (Fig. 9D) and premature ER breakdown coupled with oscillation termination in fertilized oocytes (Stricker and Smythe, 2003). Conversely, treatments with colchicine to delay MPF degradation cause persistent ER clustering and prolonged oscillations (Stricker and Smythe, 2003), presumably because under such conditions, exit from meiosis is prevented by a spindle checkpoint (Kishimoto, 2003) that remains operative after microtubular disruption. In any case, such findings indicate that a robust fertilization-induced calcium response in nemertean oocytes is associated with ER clusters that depend upon MPF activity.

As in nemerteans, mammalian oocytes form ER clusters during maturation (Kline, 2000; Mann et al., 2010), and in mice, such clusters disassemble after roscovitine treatments (FitzHarris et al., 2003). However, compared to those in nemerteans, such structures in mice tend to be smaller as well as more cortically restricted and vegetally enhanced (Stricker, 2006). In addition, unlike in nemerteans, repetitive calcium transients in mouse oocytes continue for 2 h after ER clusters have disassembled (FitzHarris et al., 2003). Nevertheless, along with altered IP3 receptor sensitivities (Wakai et al., 2011), such ER reorganizations apparently contribute in fundamental ways to shaping calcium signals in both nemertean and mammalian oocytes.


Many marine invertebrates can provide an abundant source of gametes and are thus well suited for studies of oocyte maturation and fertilization. Moreover, analyses of marine invertebrates, particularly in understudied protostome lineages, help expand perspectives in gamete biology and add to our current knowledge of these topics, which is predominantly based on studies of mammals.

As reviewed above, the regulation of oocyte maturation and fertilization exhibits some common features in nemertean and mammalian oocytes. For example, GVBD in these two groups involves the conversion of pre-MPF into active MPF and does not require intraoocytic MAPK activation. Moreover, in both types of oocytes, the ER undergoes dramatic pre--and post-fertilization reorganizations, and the fertilizing sperm triggers calcium oscillations that are apparently mediated by a soluble sperm factor that elevates IP3 levels. However, although oocyte maturation and fertilization can utilize the same general kinds of intraoocytic signals in nemerteans and mammals, marked differences can also be seen in the effects of such key modulators as AMPK, cAMP, cGMP, NO, PICA, and PKC (Fig. 10).

Some of these differences may be due to the fact that nemerteans arrest at metaphase I prior to fertilization, whereas mammalian oocytes characteristically reach metaphase II before being fertilized. Alternatively, or in addition, heterogeneous subcompartments within these oocytes could differentially affect how various signals are utilized (Webb et al., 2008: Oh et al., 2010).

Similarly, the absence versus presence of follicle cells might have influenced the particular kinds of signaling molecules that have evolved in nemertean versus mammalian oocytes. Thus, as proposed for the "cAMP paradox" in which increased cAMP levels within oocytes tend to block mammalian GVBD, whereas elevating cAMP in follicle cells can promote GVBD (Downs and Hunzicker-Dunn, 1995; Tsafriri et al., 1996: Tsafriri and Dekel, 2010), varying effects of the same signal may be due to the presence of alternative isotypes of regulators and targets for that signal. For example, cAMP's inhibitory effects on GVBD depends on type 3 PDE and type I PKA in mammalian oocytes, whereas nemertean oocytes and mammalian follicle cells seem to utilize predominantly type 4 PDE and type II PKA to stimulate GVBD (Downs and Hunzicker Dunn, 1995; Stricker and Smythe, 2001; Conti et al., 2002; Sasseville et al., 2006). Considering these and other apparent similarities between follicle cells and nemertean oocytes (Stricker, 2009b; Stricker et al., 2010a), it remains possible that nemerteans evolved intraoocytic signals that resembled those used by follicle cells in an ancestral lineage. Conversely, mammalian follicle cells might have co-opted the kinds of signaling pathways that previously existed in oocytes of a more basal group with non-follicular oogenesis.

For further testing of such hypotheses, the particular isotypes and subcellular localizations of key regulatory signals in nemertean oocytes need to be analyzed by genomic and proteomic studies conducted in conjunction with experimental manipulations and imaging methods. Similarly, to analyze the potential contributions of follicle cell versus cell cycle effects, comparative analyses could be pursued, especially in sister taxa such as molluscs, where follicle cells can be present or absent, and oocytes do not universally arrest at metaphase 1 before fertilization. In any case, currently available data indicate that oocyte maturation and fertilization in nemerteans and mammals are often regulated by similar types of signaling pathways that nevertheless can lead to fundamentally different results.


Parts of these studies were conducted at Friday Harbor Laboratories of the University of Washington with financial support from NSF (#0114319) and UNM's Research Allocation Committee. We dedicate this article to the memory of C. C. Lambert, who contributed greatly to the knowledge of marine invertebrate gametes.

Received 14 January 2013; accepted 24 May 2013.

* To whom correspondence should be addressed. E-mail: Abbreviations: AC, adenylate cyclase; AMP, adenosine monophosphate; AMPK. AMP-activated kinase; ASW, artificial seawater; CaFSW, calcium-free seawater; ER, endoplasmic reticulum; GMP, guanosine monophosphate; GV, germinal vesicle: GVBD, germinal vesicle breakdown; [IP.sub.3], inositol 1.4,5-trisphosphate: MAPK, mitogen-activated protein kinase; MPF, maturation-promoting factor; NO, nitric oxide; NOS, nitric oxide synthase: PDE, phosphodiesterase; PKA, protein kinase A; PKC, protein kinase C; PLC, phospholipase C: SFK, Src family kinase; SW. seawater.

Literature Cited

Aarabi, M., Z. Qin, W. Xu, J. Mewburn, and R. Oko. 2010. Sperm-borne protein, PAWP, initiates zygotic development in Xenopus laevis by eliciting intracellular calcium release. Mot. Reprod. Dev. 77: 249-256.

Aarabi, M., Y. Yu, W. Xu, M. Y. Tse, S. C. Pang, Y.-Y. Yia, P. Sutovsky, and R. Oko. 2012. The testicular and epididymal expression profile of PLC in mouse and human does not support its role as a sperm-borne oocyte activating factor. PLoS ONE 7: e33496; doi: 10.1371/journal.pone.0033496

Alessi. D. R., K. Sakamoto, and J. R. Bayascas. 2006. LKB1-dependent signaling pathways. Annu. Rev. Biochem. 75: 137-163.

Alexandre, H., and J. Mulnard. 1988. Time-lapse cinematography study of the germinal vesicle behaviour in mouse primary oocytes treated with activators of protein kinases A and C. Gamete Res. 21: 359-365.

Alm, H., and K. Hinrichs. 1996. Effect of cycloheximide on nuclear maturation of horse oocytes and its relation to initial cumulus morphology. J. Reprod. Fertil. 107: 215-220.

Bae, I. H., and C. P. Channing. 1985. Effect of calcium ion on the maturation of cumulus-enclosed pig follicular oocytes isolated from medium-sized Graafian follicles. Biol. Reprod. 33: 79-87.

Beckhelling, C., P. Chang, S. Chevalier, C. Ford, and E. Houliston. 2003. Pre-M phase-promoting factor associates with annulate lamellae in Xenopus oocytes and egg extracts. Mol. Biol. Cell 14: 11251137.

Bedford. S. J., S.-Y. Yoon, and R. A. Fissore. 2006. Long-lasting intracellular calcium ([[Ca.sup.2+]i]) oscillations resulting from microinjection of mouse phospholipase C zeta mRNA into mare oocytes. Anim. Reprod. Sci. 94: 294-298.

Bilodeau-Goeseels, S., M. Sasseville, C. Guillemette, and F. J. Richard. 2007. Effects of adenosine monophosphate-activated kinase activators on bovine oocyte nuclear maturation in vitro. Mol. Reprod Dev. 74: 1021-1034.

Bilodeau-Goeseels, S., P. L. Panic, and J. P. Kastelic. 2011. Activation of AMP-activated protein kinase may not be involved in AICAR- and metformin-mediated meiotic arrest in bovine denuded and cumulus-enclosed oocytes in vitro. Zygote 19: 97-106.

Bornslaeger, E. A., W. T. Pouymirou, P. Mattei, and R. M. Schultz. 1986. Effects of protein kinase C activators on germinal vesicle breakdown and polar body emission of mouse oocytes. Exp. Cell Res. 165: 507-517.

Brown, A. J., T. Jones, and J. Shutdesworth. 1994. Expression and activity of p40M015, the catalytic subunit of cdk-activating kinase, during Xenopus oogenesis and embryogenesis. Mol. Biol. Cell 5: 921932.

Byskov, A. G., C. Y. Andersen, and L. Leonardsen. 2002. Role of meiosis activating sterols, MAS, in induced oocyte maturation. Mol. Cell. Endocrinol. 187: 189-196.

Carroll, J., and K. Swann. 1992. Spontaneous cytosolic [Ca.sup.2+] oscillations driven by inositol trisphosphate occur during in vitro maturation of mouse oocytes. J. Biol. Chem. 267: 11196-11201.

Chausson, F., L. A. Paterson, K. A. Betteley, L. Hannah, L. Meijer, and M. G. Bentley. 2004. CDK1/cyclin B regulation during oocyte maturation in two closely related lugworm species. Arenicola marina and Arenicola defodiens. Der. Growth Differ. 46: 71-82.

Chen, J., and S. M. Downs. 2008. AMP-activated protein kinase is involved in hormone-induced mouse oocyte meiotic maturation in vitro. Der. Biol. 313: 47-57.

Chen. J., E. Hudson. M. M. Chi, A. S. Chang. K. H. Moley, D. G. Hardie, and S. M. Downs. 2006. AMPK regulation of mouse oocyte meiotic resumption in vitro. Der. BioL 291: 227-238.

Chen, J., M. M. Chi, K. H. Moley, and S. M. Downs. 2009. cAMP pulsing of denuded mouse oocytes increases meiotic resumption via activation of AMP-activated protein kinase. Reproduction 138: 759770.

Choi, T., F. Aoki, M. Mori, M. Yamashita. Y. Nagahama. and K. Kohmoto. 1991. Activation of p34cdc2 protein kinase in meiotic and mitotic cell cycles in mouse oocytes and embryos. Development 113: 789-795.

Coe, W. R. 1899. On the development of the pilidium of certain nemerteans. Connecticut Acad. Arts Sci. 10: 235-262.

Conti, M., C. B. Andersen, F. Richard, C. Mehats, S. Y. Chun, K. Horner, C. Jim and A. Tsafriri. 2002. Role of cyclic nucleotide signaling in oocyte maturation. Mol. Cell. Endocrinol. 187: 153-159.

Cooney, M. A., C. Malcuit, B. Cheon, M. K. Holland, R. A. Fissore, and N. T. D'Cruz. 2010. Species-specific differences in the activity and nuclear localization of murine and bovine phospholipase C zeta I. Biol. Reprod. 83: 92-101.

Coward, K., C. P. Ponting, H.-Y. Chang, 0. Hibbitt, P. Savolainen, K. T. Jones, and J. Parrington. 2005. Phospholipase CC, the trigger of egg activation in mammals, is present in non-mammalian species. Reproduction 130: 157-163.

Coward, K., C. P. Ponting, N. Zhang, C. Young, C.-J. Huang, C.-M. Chou, J. Kashir, R. A. Fissore, and J. Parrington. 2011. Identification and functional analysis of an ovarian form of the egg activation factor phospholipase C zeta (PLC[zeta]) in pufferfish. Mol. Reprod. Dev. 78: 48-56.

Deguchi, R. 2007. Fertilization causes a single [Ca.sup.2+] increase that fully depends on [Ca.sup.2+] influx in oocytes of limpets (Phylum Mollusca, Class Gastropoda). Dev. Biol. 304: 652-663.

Deguchi, R., K. Osanai, and M. Morisawa. 1996. Extracellular [Ca.sup.2+] entry and [Ca.sup.2+] release from inositol I. 4. 5-trisphosphate-sensitive stores function at fertilization in oocytes of the marine bivalve Mytilus Mulls. Development 122: 3651-3660.

Deguchi, R., H. Shirakawa S. Oda, T. Mohri, and S. Miyazaki. 2000. Spatiotemporal analysis of [Ca.sup.2+] waves in relation to the sperm entry site and animal vegetal axis during [Ca.sup.2+] oscillations in fertilized mouse eggs. Dev. Biol. 257: 166-176.

Deguchi, R., E. Kondoh, and J. Itoh. 2005. Spatiotemporal characteristics and mechanisms of intracellular [Ca.sup.2+] increases at fertilization in eggs of jellyfish (Phylum Cnidaria, Class Hydrozoa). Dev. Biol. 279: 291-307

Deguchi, R., N. Takeda, and S. A. Stricker. 2011. Comparative biology of cAMP-induced germinal vesicle breakdown in marine invertebrate oocytes. Mol. Reprod. Dev. 78: 708-725.

Dekel, N., D. Galiani, and I. Sheriziy. 1988. Dissociation between the inhibitory and the stimulatory action of cAMP on maturation of rat oocytes. Mol. Cell. Endocrinol. 56: 115-121.

Denys, A., N. Avazeri, and B. Lefevre. 2007. The PKC pathway and in particular its beta 1 isoform is clearly involved in meiotic arrest maintenance but poorly in FSH-induced meiosis resumption of the

mouse cumulus cell enclosed oocyte. Mol. Reprod. Dev. 74: 15751580.

Downs, S. M. 2010. Regulation of the G2/M transition in rodent oocytes. Mol. Reprod.. Dev. 77: 566-585.

Downs, S. M. 2011. Mouse versus rat: profound differences in meiotic regulation at the level of the isolated oocyte. Mol. Reprod. Dev. 78: 778-794.

Downs, S. M., and M. Hunzicker-Dunn. 1995. Differential regulation of oocyte maturation and cumulus expansion in the mouse oocyte-cumulus cell complex by site-selective analogs of cyclic adenosine monophosphate. Dev. Biol. 172: 72-85.

Downs, S. M., J. Cottom, and M. Hunzicker-Dunn. 2001. Protein kinase C and meiotic regulation in isolated mouse oocytes. Mol. Reprod. Dev. 58: 101-115.

Downs, S. M., E. R. Hudson, and D. G. Hardie. 2002. A potential role for AMP-activated protein kinase in meiotic induction in mouse oocytes. Dev. Biol. 245: 200-212.

Ducibella. T., and R. Fissore. 2008. The roles of [Ca.sup.2+], downstream protein kinases, and oscillatory signaling in regulating fertilization and the activation of development. Dev. Biol. 315: 257-279.

Dumollard, R.. J. Carroll, G. Dupont, and C. Sardet. 2002. Calcium wave pacemakers in eggs. J. Cell Sci. 115: 3557-3564.

Dupont, G., and R. Dumollard, R. 2004. Simulation of calcium waves in ascidian eggs: insights into the origin of the pacemaker sites and the possible nature of the sperm factor. J. Cell Sci. 117: 4313-4323.

Dupont, G., 0. M. McGuinness, M. H. Johnson, M. J. Berridge, and F. Borgese. 1996. Phospholipase C in mouse oocytes: characterization of beta and gamma isoforms and their possible involvement in sperm-induced [Ca.sup.2+] spiking. Biochem. J. 316: 583-591.

Edwards, R. G., and A. H. Gates. 1959. Timing of the stages of the maturation divisions, ovulation, fertilization and the first cleavage of eggs of adult mice treated with gonadotrophins. J. Endocrinol. 18: 292-304.

Eisen, A., and G. A. Reynolds. 1985. Sources and sinks for the calcium released during fertilization of single sea urchin eggs. J. Cell Biol. 100: 1522-1527.

Ekholm, C., and C. Magnusson. 1979. Rat oocyte maturation: effects of protein synthesis inhibitors. Biol. Reprod. 21: 1287-1293.

Esacalona. R., and S. A. Stricker. 2013. Immunoblotting analyses of changes in protein phosphorylations during oocyte maturation in marine nemertean worms. In Methods in Molecular Biology: Developmental Biology of the Sea Urchin and Other Marine Invertebrate Model Systems, D. J. Carroll and S. A. Stricker, eds. Humana Press, New York. In press.

Evans, J., and B. Gadella. 201.1. Membrane fusions during mammalian fertilization. Adv. Exp. Med. Biol. 713: 65-80.

Faerge, I., B. Terry, J. Kalous, P. Wahl, M. Lessl, J. L. Ottesen, P. Hyttel. and C. Grondahl. 2001. Resumption of meiosis induced by meiosis-activating sterol has a different signal transduction pathway than spontaneous resumption of meiosis in denuded mouse oocytes cultured in vitro. Biol. Reprod. 65: 1751-1758.

Fan, H.-Y., and Q.-Y. Sun. 2004. Involvement of mitogen-activated protein kinase cascade during oocyte maturation and fertilization in mammals. Biol. Reprod. 70: 535-547.

Fan. H.-Y., L.-J. Huo, D.-Y. Chen, H. Schatten, and Q.-Y. Sun. 2004. Protein kinase C and mitogen-activated protein kinase cascade in mouse cumulus cells: cross talk and effect on meiotic resumption of oocyte. Biol. Reprod. 70: 1178-1 187.

Fan, H.-Y., Z. Liu, M. Shimada, E. Sterneck, P. F. Johnson, S. M. Hedrick, and J. S. Richards. 2009. MAPK3/1 (ERK1/2) in ovarian granulosa cells are essential for female fertility. Science 324: 938-941.

FitzHarris, G., P. Marangos, and J. Carroll. 2003. Cell cycle-dependent regulation of structure of endoplasmic reticulum and inositol

1,4,5-trisphosphate induced [Ca.sup.2+] release in mouse oocytes and embryos. Mol. Biol. Cell 14: 288-301.

Freeman, G. 1978. The role of asters in the localization of the factors that specify the apical tuft and the gut of the nemertine Cerebratulus lacteus. J. Exp. Zool. 206: 81-107.

Freeman, G., and E. B. Ridgway. 1988. The role of cAMP in oocyte maturation and the role of the germinal vesicle contents in mediating maturation and subsequent developmental events in hydrozoans. Roux's Arch. Dev. Biol. 197: 197-211.

Fujii, W., T. Nishimura, K. Kano, K. Sugiura. and K. Naito. 2011. CDK7 and CCNH are components of CDK-activating kinase and are required for meiotic progression of pig oocytes. Biol. Reprod. 85: 1124-1132.

Fulka, J., Jr., J. Motlik, J. Fulka, and F. Jilek. 1986. Effect of cycloheximide on nuclear maturation of pig and mouse oocytes. J. Reprod. Fertil. 77: 281-285.

Gaffre, M., A. Martoriati, N. Belhachemi, J. P. Chambon, E. Houliston, C. Jessus, and A. Karaiskou. 2011. A critical balance between Cyclin B synthesis and Myt1 activity controls meiosis entry in Xenopus oocytes. Development 138: 3735-3744.

Gallicano, G. L, S. M. Schwarz, R. W. McGaughey, and D. G. Capco. 1993. Protein kinase C, a pivotal regulator of hamster egg activation, functions after elevation of intracellular free calcium. Dev. Biol. 156: 94-106.

Gilchrist, R. B. 2011. Recent insights into oocyte-follicle cell interactions provide opportunities for the development of new approaches to in vitro maturation. Reprod. Fertil. Dev. 23: 23-31.

Goren., S., Y. Oron. and N. Dekel. 1990. Rat oocyte maturation: role of calcium in hormone action. Mol. Cell. Endocrinol. 72: 131-138.

Grange, L. J., L. S. Peck, and P. A. Tyler. 2011. Reproductive ecology of the circumpolar Antarctic nemertean Parborlasia corrugatus: no evidence for inter-annual variation. J. Exp. Mar. Biol. Ecol. 404: 98-107.

Griffin, J., B. R. Emery. I. Haan. C. M. Peterson., and D. T. Carrell. 2006. Comparative analysis of follicle morphology in four mammalian species ( mouse, hamster. pig. and human). J. Exp. Clin. Assist. Reprod. 3: doi: 10.1186/1743-1050-3-2.

Harada, Y., T. Matsumoto, S. Hirahara, A. Nakashima, S. Ueno, S. Oda, S. Miyazaki, and Y. Iwao. 2007. Characterization of a sperm factor for egg activation at fertilization of the newt Cynops pyrrho-gaster. Dev. Biol. 306: 797-808.

Harada, Y., M. Kawazoe, Y. Eto, S. Ueno, and Y. Iwao. 2011. The [Ca.sup.2+] increase by the sperm factor in physiologically polysperrnic newt fertilization: its signaling mechanism in egg cytoplasm and the species-specificity. Dev. Biol. 351: 266-276.

Hardie, D. G. 2007. AMP-activated/SNF1 protein kinases: conserved guardians of cellular energy. Nat. Rev. Mol. Cell. Biol. 8: 774-785. Hartman, C. G. 1929. How large is the mammalian egg?: A review. Q. Rev. Biol. 4: 373-388.

Hegele-Hartung, C., J. Kulinke, M. Lessl, C. Grandahl, J. Ottesen, H. M. Beier, S. Eisner, and U. Eichenlaub-Ritter. 1999. Nuclear and cytoplasmic maturation of mouse oocytes after treatment with synthetic meiosis-activating sterol in vitro. Bea Reprod, 61: 13621372.

Heytens, E., J. Parrington, K. Coward, C. Young, S. Lambrecht, S.-Y. Yoon, R. A. Fissore. R. Hamer, C. M. Deane, M. Ruas, et al. 2009. Reduced amounts and abnormal forms of phospholipase C zeta (PLC[zeta]) in spermatozoa from infertile men. Hum. Reprod. 24: 2417-2428.

Homa, S. T. 1995. Calcium and meiotic maturation of the mammalian oocyte. Mol. Reprod. Dev. 40: 122-134.

Ito, J., and N. Kashiwazaki. 2012. Molecular mechanisms of fertilization in the pig. Animal Sci. J. 83: 669-672.

Ito, J., S.-Y. Yoon, B. Lee, V. Vanderheyden. E. Vermassen, R. Wojcikiewicz, D. Alfandari, H. De Smedt, J. B. Parys, and R. A.

Fissore. 2008. Inositol 1,4,5 trisposphate receptor 1, a widespread [Ca.sup.2+] channel, is a novel substrate of polo-like kinase 1 in eggs. Dev. Biol. 320: 402-413.

Ito, J., J. Parrington, and R. A. Fissore. 2011. PLC[zeta]ae and its role as a trigger of development in vertebrates. Mol. Reprod. Dew. 78: 846-853.

Jaffe, L., D. Kline, and R. Tucker. 1985. Fertilization potential and polyspermy prevention in the egg of the nemertean. Cerebratulus lacteus. J. Exp. Zool. 236: 45-52.

Jaffe, L. A., and R. P. Norris. 2010. Initiation of the meiotic prophase-to-metaphase transition in mammalian oocytes. Pp. 181-198 in Oogenesis: The Universal Process, M.-H. Verlhac and A. Villeneuve, eds. John Wiley, New York.

Jones, K. T. 1998. [Ca.sup.2+] oscillations in the activation of the egg and development of the embryo in mammals. Int. J. Dev. Biol. 42: 1-10.

Jones, K. T. 2004. Turning it on and off: M-phase promoting factor during meiotic maturation and fertilization. Mol. Hum. Reprod. 10: 1-5.

Jones, K. T. 2007. Intracellular calcium in the fertilization and development of mammalian eggs. Clin. Exp. Pharmacol. Physiol. 34: 10841089.

Jones, K. T., J. Carroll, J. A. Merriman, D. G. Whittingham, and T. Kono. 1995. Repetitive sperm-induced calcium transients in mouse oocytes are cell cycle dependent. Development 121: 3259-3266.

Kajihara. H., A. V. Chernyshev, S.-C. Sun, P. Sundberg, and F. B. Crandall. 2008. Checklist of nemertean genera and species (Nemertea) published between 1995 and 2007. Species Diversity 13: 245274.

Kang, M. K.. and S. J. Han. 2011. Post-transcriptional and post-translational regulation during mouse oocyte maturation. Biochem. Mol. Biol. Rep. 44: 147-157.

Kashir, J., B. Heindryckx, C. Jones, P. De Sutter. J. Parrington, and K. Coward. 2010. Oocyte activation. phospholipase C zeta and human infertility. Hum. Reprod. Update 16: 690-703.

Kashir. J., C. Jones, and K. Coward. 2012. Calcium oscillations, oocyte activation, and phospholipase C zeta. Adv. Exp. Med. Biol. 740: 1095-1121.

Kastrop, P. M. M. S. C. J. Sulshof, M. M. Bevers, 0. H. J. Destree, and T. A. M. Kruip. 1991. The effects of a-amanitin and cycloheximide on nuclear progression, protein synthesis, and phosphorylation during bovine oocyte maturation in vivo. Mol. Reprod. Dev. 28: 249-254.

Kaufman, M. H. 1973. Timing of the first cleavage division of the mouse and the duration of its component stages: a study of living and fixed eggs. J. Cell Sci. 12: 799-808.

Kishimoto, T. 2003. Cell-cycle control during meiotic maturation. Curr. Opin. Cell Biol. 15: 654-663.

Kline, D. 2000. Attributes and dynamics of the endoplasmic reticulum in mammalian oocytes. Curr. Top. Dev. Biol, 50: 124-154.

Kovo, M., M. Kandli-Cohen, M. Ben-Haim, D. Galiani, D. W. Carr, and N. Dekel. 2006. An active protein kinase A (PKA) is involved in meiotic arrest of rat growing oocytes. Reproduction 132: 33-43.

Kyozuka, K., R. Deguchi, T. Mohri, and S. Miyazaki. 1998. Injection of sperm extract mimics spatiotemporal dynamics of calcium responses and progression of meiosis at fertilisation of ascidian oocytes. Development 125: 4099-4105.

Lambert, C. C. 2008. Signaling pathways in ascidian oocyte maturation: the role of cyclic AMP and follicle cells in germinal vesicle breakdown. Dev. Growth Differ. 50: 181-188.

Larman, M. G., C. M. Saunders, J. Carroll, F. A. Lai, and K. Swann. 2004. Cell cycle dependent [Ca.sup.2+] oscillations in mouse embryos are regulated by nuclear targeting of PLCzeta. J. Cell Sci. 117: 2513-2521.

LaRosa, C.. and S. M. Downs. 2006. Stress stimulates AMP-activated protein kinase and meiotic resumption in mouse oocytes. Biol. Reprod. 74: 585-592.

LaRosa, C., and S. M. Downs. 2007. Meiotic induction by heat stress in mouse oocytes: involvement of AMP-activated protein kinase and MAPK family members. Biol. Reprod. 76: 476-486.

Lee, B., E. Vermassen, S.-Y. Yoon, V. Vanderheyden, J. Ito, D. Alfan-dari, H. De Smedt, J. B. Parys, and R. A. Fissore. 2006. Phosphorylation of IP3R1 and the regulation of [Ca.sup.2+]i response at fertilization: a role for the MAP kinase pathway. Development 133: 4355-4365.

Le Gal, F., L. Gall, and V. De Smedt. 1992. Changes in protein synthesis pattern during in vitro maturation of goat oocytes. Mol. Reprod. Dev. 32: 1-8.

Lefevre, B., A. R. Pesty, K. Kozialc, and J. Testart. 1992. Protein kinase C modulators influence meiosis kinetics but not fenilizability of mouse oocytes. J. Exp. Zool. 264: 206-213.

Levasseur, M., M. Carroll, K. T. Jones, and A. McDougall. 2007. A novel mechanism controls the [Ca.sup.2+] oscillations triggered by activation of ascidian eggs and has an absolute requirement for Cdkl activity. J. Cell Sci. 120: 1763-1771.

Li, Y. X. 2003. Tango waves in a bidomain model of fertilization calcium waves. Plipica D. 186: 27-49.

Liang, C.-G., Y.-Q. Su, H.-Y. Fan, H. Schatten, and Q.-Y. Sun. 2007. Mechanisms regulating oocyte meiotic resumption: roles of mitogen-activated protein kinase. Mol. Endocrinol. 21: 2037-2055.

Lu, Q., G. D. Smith, D.-Y. Chen, Z.-M. Han. H. Schatten. and Q.-Y. Sun. 2001. Phosphorylation of mitogen-activated protein kinase is regulated by protein kinase C. cyclic 3',5'-adenosine monophosphate. and protein phosphatase modulators during meiosis resumption in rat oocytes. Biol. Reprod. 64: 1444-1450.

Luria, A, T. Tennenbaum, Q. Y. Sun, S. Rubinstein, and H. Breitbart. 2000. Differential localization of conventional protein kinase C isoforms during mouse oocyte development. Biol. Reprod. 62: 1564-1570.

Mann, J. S., K. M. Lowther, and L. M. Mehlmann. 2010. Reorganization of the endoplasmic reticulum and development of [Ca.sup.2+] release mechanisms during meiotic maturation of human oocytes. Biol. Re-prod. 83: 578-583.

Marangos, P., G. FitzHarris, and J. Carroll. 2003. [Ca.sup.2+] oscillations at fertilization in mammals are regulated by the formation of pronuclei. Development 130: 1461-1472.

Mattioli, M., G. Galeati, B. Barboni, and E. Seren. 1994. Concentration of cyclic AMP during the maturation of pig oocytes in vivo and in vitro. J. Reprod. Fend. 100: 403-409.

Matzuk, M. H., K. H. Burns, M. M. Viveiros, and J. J. Eppig. 2002. Intercellular communication in the mammalian ovary: oocytes carry the conversation. Science 296: 2178-2180.

Mayes, M. A.. M. F. Laforest, C. Guillemette, R. B. Gilchrist, and F. J. Richard. 2007. Adenosine 5' -monophosphate kinase-activated protein kinase (PRKA) activators delay meiotic resumption in porcine oocytes. Biol. Reprod. 76: 589-597.

McDougall, A., M. Levasseur, A. J. O'Sullivan, and K. T. Jones. 2000. Cell cycle-dependent repetitive [Ca.sup.2+] waves induced by a cytosolic sperm extract in mature ascidian eggs mimic those observed at fertilization. J. Cell Sci. 113: 3453-3462.

McDougall, A., J. Chenevert. and R. Dumollard. 2012. Cell cycle control in oocytes and early embryonic cleavage cycles in ascidians. Mt. Rev. Cell Mol. Biol. 297: 235-264.

McGinnis, L. K., D. J. Carroll, and W. H. Kinsey. 2011. Protein tyrosine kinase signaling during oocyte maturation and fertilization. Mol. Reprod. Dev. 78: 831-845.

Mehlmann, L. M. 2005. Stops and starts in mammalian oocytes: recent advances in understanding the regulation of meiotic arrest and oocyte maturation. Reproduction 130: 791-799.

Mehlmann, L. M., R. R. Kalinowski, L F. Ross, A. F. Parlow. E. L. Hewlett, and L. A. Jaffe. 2006. Meiotic resumption in response to

luteinizing hormone is independent of a Gi family G protein or calcium in the mouse oocyte. Dev. Biol. 299: 345-355.

Meng, L., J. Luo, C. Li, and W. H. Kinsey. 2006. Role of Src homology 2 domain-mediated PTK signaling in mouse zygotic development. Reproduction 132: 413-422.

Miao, Y.-L., and C. J. Williams. 2012. Calcium signaling in mammalian egg activation and embryo development: the influence of subcellular localization. Mol. Reprod. Dev. 79: 742-756.

Miyata, K., T. Nakano, R. Kuroda, and H. Kuroda. 2006. Development of calcium releasing activity induced by inositol trisphosphate and cyclic ADP-ribose during in vitro maturation of sea urchin oocytes. Dev. Growth Differ. 48: 605-613.

Miyazaki, S. 2006. Thirty years of calcium signals at fertilization. Semin. Cell Dev. Biol. 17: 233-243.

Miyazaki, S., M. Yuzaki, K. Nakada, H. Shirakawa, S. Nakanishi, S. Nakade, and K. Mikoshiba. 1993. Block of [Ca.sup.2+] wave and [Ca.sup.2+] oscillation by antibody to the inositol 1,4,5-trisphosphate receptor in fertilized hamster eggs. Science 257: 251-255.

Motlik, J., J. Fulka Jr., R. Prochazka, Z. Rimkevicova, M. Kulbelka, and J. Punta. 1989. RNA and protein synthesis requirements for the resumption of meiosis in rabbit oocytes: the role of cumulus cells. Reprod. Nutr. Dev. 29: 601-609.

Motoshima, H., B. J. Goldstein, M. Igata, and E. Araki. 2006. AMPK and cell proliferation--AMPK as a therapeutic target for atherosclerosis and cancer. J. Physiol. 574: 63-71

Nakamura, Y., Y. Yamagata, N. Sugino, H. Takayama, and H. Kato. 2002. Nitric oxide inhibits oocyte meiotic maturation. Biol. Reprod. 67: 1588-1592.

Nogueira, D., J. C. Sadeu, and J. Montagut. 2012. In vitro oocyte maturation: current status. Semin. Reprod. Med. 30: 199-213.

Nomikos, M., K. Swann, and F. A. Lai. 2012. Starting a new life: sperm PLC-zeta mobilizes the [Ca.sup.2+] signal that induces egg activation and embryo development. Bioessuysv 34: 126-134

Norenburg, J. L., and S. A. Stricken 2002. Phylum Nemertea. Pp. 163-179 in Atlas of Marine Invertebrate Larvae, C. Young. M. A. Sewel, and M. Rice. eds. Academic Press. San Diego.

Oh, J. S., S. J. Han. and M. Conti. 2010. WeelB. Mytl, and Cdc25 function in distinct compartments of the mouse oocyte to control meiotic maturation. J. Cell Biol. 188: 199-207.

Paleos, G. A., and R. D. Powers. 1981. The effect of calcium on the first meiotic division of the mammalian oocyte. J. Exp. Zool. 217: 409416.

Park, J. Y., V. Q. Su, M. Ariga, E. Law, S. L. Jin, and M. Conti. 2004. EGF-like growth factors as mediators of LH action in the ovulatory follicle. Science 303: 682-684.

Parrington, J., L. C. Davis, A. Galione, and G. Wessel. 2007. Flipping the switch: how a sperm activates the egg at fertilization. Dev. Dyn. 236: 2027-2038.

Pirino, G., M. P. Wescott, and P. J. Donovan. 2009. Protein kinase A regulates resumption of meiosis by phosphorylation of Cdc25B in mammalian oocytes. Cell Cycle 8: 665-670.

Plancha, C. E., and D. F. Albertini. 1992. Protein synthesis requirements during resumption of meiosis in the hamster oocyte--early nuclear and microtubule configurations. Mol. Reprod. Dev. 33: 324-332.

Quan, H.-M., H.-Y. Fan, X.-Q. Meng, D.-Y. Chem H. Schatten, P.-M. Yang, and Q.-Y. Sun. 2003. Effects of PKC activation of the meiotic maturation, fertilization and early development of mouse oocytes. Zygote 11: 329-337.

Ramadan, W. M., J. Kashir, C. Jones, and K. Coward. 2012. Oocyte activation and phospholipase C zeta (PLC[zeta]): diagnostic and therapeutic implications for assisted reproductive technology. Cell Comm. Signal. 10: doi: 10.1186/1478-811X-10-12

Rodrigues, P., D. Limback. L. McGinnis, C. E. Plancha, and D. F.

Albertini. 2008. Oogenesis: prospects and challenges for the future. J. Cell. Physiol. 216: 355-365.

Runk L. L., and L. A. Jaffe. 2000. Sperm extract injection into ascidian eggs signals [Ca.sup.2+] release by the same pathway as fertilization. Development 127: 3227-3236.

Runft, L., L. A. Jaffe, and L. M. Mehlmann. 2002. Egg activation at fertilization: where it all begins. Der. Biol. 245: 237-254.

Satoshi. A.. S. Petrungaro, M. De Felice, M. Conti. and G. Siracusa. 1985. Effect of follicle-stimulating hormone on cyclic adenosine monophosphate level and on meiotic maturation in mouse cumulus cell-enclosed oocytes cultured in vitro. Biol. Reprod. 33: 797-802.

SanteIla, L., F. Vasilev, and J. T. Chun. 2012. Fertilization in echinoderms. Biochim. Biophys. Res. Comm. 425: 588-594.

Sardet, C., F. Romiers, R. DumoHard, C. Rouviere, and A. McDougall. 1998. Calcium waves and oscillations in eggs. Biophys. Chem. 72: 131-140.

Sasseville, M., N. Cote, C. Guillemette. and F. J. Richard. 2006. New insight into the role of phosphodiesterase 3A in porcine oocyte maturation. BMC Der. Biol. 6: doi:10.1186/1471-213X-6-47

Schroeder, T. E., and S. A. Stricken 1983. Morphological changes during maturation of starfish oocytes: surface ultrastructure and cortical actin. Der. Biol. 98: 373-384.

Schultz, R. M., and P. M. Wasserman. 1977. Biochemical studies of mammalian oogenesis: protein synthesis during oocyte growth and meiotic maturation in the mouse. J. Cell Sci. 24: 167-194.

Sela-Abramovich. S., D. Galiani, N. Nevo. and N. Dekel. 2008. Inhibition of rat oocyte maturation and ovulation by nitric oxide: mechanism of action. Biol. Reprod. 78: 1111-1118.

Shalgi, R., R. Kaplan, and P. F. Kraicer. 1985. The influence of postovulatory age on the rate of cleavage in in vitro fertilized rat oocytes. Gamete Res. 11: 99-106.

Silvestre, F., R. Boni, R. A. Fissore, and E. Tosti. 2011. [Ca.sup.2+] signaling during maturation of cumulus-oocyte complex in mammals. Mol. Reprod. Dev. 78: 744-756.

Smythe, T. L., and S. A. Stricken 2005. Germinal vesicle breakdown is not fully dependent on MAPK activation in maturing oocytes of marine nemertean worms. Mol. Reprod. Dev. 70: 91-102.

Sohinoff, A. P, J. M. Sutherland, and E. A. McLaughlin. 2012. Intracellular signalling during female gametogenesis. Mol. Hum. Reprod. doi: 10.1093/molehr/gas065.

Sole, P., R. M. Schultz, and J. Malik. 2010. Prophase I arrest and progression to metaphase I in mouse oocytes: comparison of resumption or meiosis and recovery from G2-arrest in somatic cells. Mal. Hum. Reprod. 16: 654-664.

Stricker, S. A. 1982. The morphology of Paranemertes sanjuanensis sp. n. (Nemertea, Monostilifera) from Washington. USA. Zool. Scr. 11: 107-115.

Stricker, S. A. 1985. A new species of Tetrastemma (Nemertea, Mono-stilifera) from San Juan Island, Washington, U.S.A. Can. J. Zool. 63: 682-690.

Stricken S. A. 1986. An ultrastructural study of oogenesis. fertilization. and egg laying in a nemertean ectosymbiont of crabs, Carcinonemertes epialti (Nemertea, Hoplonemertea). Can. J. Zool. 64: 1256-1269.

Stricken S. A. 1987. Phylum Nemertca. Pp. 129-137 in Reproduction and Development of Marine Invertebrates of the Northern Pacific Coast, M. Strathmann, ed. Univ. Washington Press, Seattle.

Stricken S. A. 1995. Time-lapse confocal imaging of calcium dynamics in starfish embryos. Dev. Biol. 170: 496-518.

Stricker, S. A. 1996. Repetitive calcium waves induced by fertilization in the nemertean worm Cerebratulus lacteus. Dev. Biol. 176: 243-363.

Stricker, S. A. 1997. Intracellular injections of a soluble sperm factor trigger calcium oscillations and meiotic maturation in the unfertilized oocytes of a marine worm. Dev. Biol. 186: 185-201.

Stricker, S. A. 1999. Comparative calcium signaling during fertilization and egg activation in animals. Del.. Biol. 211: 157-176.

Stricker, S. A. 2000. Confocal microscopy of intracellular calcium dynamics during fertilization. BioTechniques 29: 492-498.

Stricker, S. A. 2004. Dual-channel confocal ratioing of calcium dynamics in living eggs and oocytes. Pp. 137-148 in Germ Cell Protocols, Vol. 2, H. Schatten. ed. Humana Press, Totowa, NJ.

Stricker, S. A. 2006. Structural reorganizations of the endoplasmic reticulum during egg maturation and fertilization. Semin. Cell Dev. Biol. 17: 303-313.

Stricker, S. A. 2009a. Roles of protein kinase C isotypes during seawater-versus cAMP-induced oocyte maturation in a marine worm. Mol. Reprod. Dev. 76: 693-707.

Stricker, S. A. 2009b. Interactions between mitogen-activated protein kinase and protein kinase C signaling during oocyte maturation and fertilization in a marine worm. Mol. Reprod. Dev. 76: 708-721.

Stricker, S. A. 2011. Potential upstream regulators and downstream targets of AMP-activated kinase (AMPK) during oocyte maturation in a marine worm. Reproduction 142: 29-39.

Stricker, S. A. 2012. Inhibition of germinal vesicle breakdown by antioxidants and the roles of signaling pathways related to nitric oxide and cGMP during meiotic resumption in oocytes of a marine worm. Reproduction 143: 261-270.

Stricker, S. A., and M. W. Folsom. 1998. A comparative ultrastructural analysis of spermatogenesis in nemertean worms. Hydrobiologia 365: 55-72.

Stricker, S. A., and T. L. Smythe. 2000. Multiple triggers of oocyte maturation in nemertean worms: the roles of calcium and serotonin. J. Exp. Zool. 287: 243-261.

Stricker, S. A., and T. L. Smythe 2001. 5-HT causes an increase in cAMP that stimulates, rather than inhibits, oocyte maturation in marine nemertean worms. Development 128: 1415-1427.

Stricker, S. A.. and T. L. Smythe. 2003. Endoplasmic reticulum reorganizations and [Ca.sup.2+] signaling in maturing and fertilized oocytes of marine protostome worms: the roles of MAPKs and MPF. Development 130: 2867-2879.

Stricker. S. A., and T. L. Smythe. 2006a. Differing mechanisms of cAMP-versus seawater-induced oocyte maturation in marine nemertean worms. I. The roles of serine/threonine kinases and phosphatases. Mol. Reprod. Dev. 73: 1578-1590.

Stricker, S. A., and T. L. Smythe. 2006b. Differing mechanisms of cAMP--versus seawater-induced oocyte maturation in marine nemer-tean worms. IL The roles of tyrosine kinases and phosphatases. Mol. Reprod. Dev. 73: 1564-1577.

Stricker, S. A., and M. Whitaker. 1999. Confocal laser scanning microscopy of calcium dynamics in living cells. Mier. Res. Tech. 46: 356-369.

Stricker, S. A., V. E. Centonze, S. W. Paddock, and G. Schatten. 1992. Confocal microscopy of fertilization-induced calcium dynamics in sea urchin eggs. Dev. Biol. 149: 370-380.

Stricker, S. A., R. Silva, and T. Smythe. 1998. Calcium and endoplasmic reticulum dynamics during oocyte maturation and fertilization in the marine worm Cerehratulus lacteus. Dev. Biol. 203: 305-322.

Stricker, S. A., K. Swann, K. T. Jones, and R. A. Fissore. 2000. Injections of porcine sperm extracts trigger fertilization-like calcium oscillations in oocytes of a marine worm. Exp. Cell Res. 257: 341-347.

Stricker, S. A., T. L. Smythe. L. Miller. and J. L. Norenburg. 2001. Comparative biology of oogenesis in nemertean worms. Acta Zool. 82: 213-230.

Stricker, S. A., J. R. Escalona, S. Abernathy, and A. Marquardt. 2010a. Pharmacological analyses of protein kinases regulating egg maturation in marine nemertean worms: a review and comparison with mammalian eggs. Mar. Drugs 8: 2417-2434.

Stricker, S. A., L. Swiderek, and T. Nguyen. 2010b. Stimulators of

AMP-activated kinase inhibit seawater--but not cAMP-induced oocyte maturation in a marine worm: implications for interactions between cAMP and AMPK signaling. Mol. Reprod. Dev. 77: 497-510.

Stricker, S. A., D. J. Carroll, and W. L. Tsui. 2010c. Roles of Src family kinases during fertilization and the first cell cycle in the marine protostome worm Cerebratulus. Int. J. Dev. Biol. 54: 787-793.

Struck, T., and F. Fisse. 2008. Phylogenetic position of Nemertea derived from phylogenomic data. Mol. Biol. Evol. 25: 728-736.

Su, Y. Q., G. L. Xia, A. G. Byskov, C. D. Fu, and C. R. Yang. 1999. Protein kinase C and intracellular calcium are involved in follicle-stimulating hormone-mediated meiotic resumption of cumulus cell-enclosed porcine oocytes in hypoxanthine-supplemented medium. Mol. Reprod. Dev. 53: 51-58.

Su, Y. Q., K. Sugiura, Q. Li, K. Wigglesworth, M. M. Matzuk, and J. J. Eppig. 2010. Mouse oocytes enable LH-induced maturation of the cumulus--oocyte complex via promoting EGF receptor-dependent signalling. Mol. Endocrinol. 24: 1230-1239.

Sun, Q. Y., Y. L. Miao, and H. Schatten. 2009. Towards a new understanding on the regulation of mammalian oocyte meiosis resumption. Cell Cycle 8: 2741-2747.

Suwa, K., and M. Yamashita. 2007. Regulatory mechanisms of oocyte maturation and ovulation. Pp. 323-347 in The Fish Oocyte: From Basic Studies to Biotechnological Applications, P. J. Babin, J. Cerda, and E. Lubzens, eds. Springer, Dordrecht.

Swarm, K., and F. A. Lai. 2013. PLC[zeta] and the initiation of [Ca.sup.2+] oscillations in fertilizing mammalian eggs. Cell Calcium doi: 10.1016/j.ceca.2012.11.001.

Swann. K., and Y. S. Yu. 2008. The dynamics of calcium oscillations that activate mammalian eggs. Int. J. Dev. Biol. 52: 585-594.

Takeda, N., K. Kyozuka, and R. Deguchi. 2006. Increase in intracellular cAMP is a prerequisite signal for initiation of physiological oocyte meiotic maturation in the hydrozoan Cytaeis uchidae. Dev. Biol. 298: 248-258.

Talmor-Cohen, A., R. Tomashov-Matar, E. Eliyahu, R. Shapiro. and R. Shalgi. 2004. Are Src family kinases involved in cell cycle resumption in rat eggs? Reproduction 127: 455-463.

Taylor, S. S., J. Yang, J. Wu, N. M. Haste, E. Radzio-Andzelm, and G. Annand. 2004. PKA: a portrait of protein kinase dynamics. Biochim. Biophys. Acta 1697: 259-269.

Terasaki, M., and L. A. Jaffe. 2004. Labeling of cell membranes and compartments for live cell fluorescence microscopy. Methods Cell Biol. 74: 469-489.

Tombes, R. M., C. Simerly, G. G. Borisy, and G. Schatten. 1992. Meiosis, egg activation, and nuclear envelope breakdown are differentially reliant on [Ca.sup.2+]. whereas germinal vesicle breakdown is [Ca.sup.2+] independent in the mouse oocyte. J. Cell Biol. 117: 799-811.

Tosca, L., S. Uzbekova, C. Chabrolle, and J. Dupont. 2007. Possible role of 5' AMP-activated protein kinase in the metformin-mediated arrest of bovine oocytes at the germinal vesicle stage during in vitro maturation. Biol. Reprod. 77: 452-465.

Tosti, E. 2006. Calcium ion currents mediating oocyte maturation events. Reprod. Biol. Endocrinol. 4: 26-35.

Tripathi, A., S. Khatun, A. N. Pandey, S. K. Misbra, R. Chaube, T. G. Shrivastav, and S. K. Chaube. 2009. Intracellular levels of hydrogen peroxide and nitric oxide in oocytes at various stages of meiotic cell cycle and apoptosis. Free Radic. Res. 43: 287-294.

Tripathi, A., K. V. Kumar, and S. K. Chaube. 2010. Meiotic cell cycle arrest in mammalian oocytes. J. Cell. PhysioL 223: 592-600.

Tsafriri, A., and N. Dekel. 2010. Intra--and intercellular molecular mechanisms in regulation of meiosis in murid rodents. Pp. 38-63 in Oocyte Maturation and Fertilization: A Long History for a Short Event. E. Tosti and R. Boni, eds. Bentham Science Publishers. [Online.] Available: [2013. July 11].

Tsafriri, A., H. R. Lindner, U. Zor, and S. A. Lamprecht. 1972. In vitro induction of meiotic division in follicle-enclosed rat oocytes by LH, cAMP, and prostaglandin E. J. Reprod. Fend. 31: 39-50.

Tsafriri, A., S.-Y. Chun, R. Zhang, A. J. W. Hsueh, and M. Conti. 1996. Oocyte maturation involves compartmentalization and opposing changes of cAMP levels in follicular somatic and germ cells: studies using selective phosphodiesterase inhibitors. Dev. Biol. 178: 393-402.

Vacquier, V. D. 2011. Laboratory on sea urchin fertilization. Mol. Reprod. Dev. 78: 553-564.

Voronina, E., and G. M. Wessel. 2003. The regulation of oocyte maturation. Curr. Top. Dev. Biol. 58: 53-110.

Wakai, T., V. Vanderheyden, and R. A. Fissore. 2011. [Ca.sup.2+] signaling during mammalian fertilization: requirements, players. and adaptations. Cold Spring Harb. Perspect. Biol. doi: 10.1101/cshperspect.a006767.

Webb, R. J., L. Tinworth, G. M. H. Thomas, M. Zaccolo, and J. Carroll. 2008. Developmentally acquired PICA localization in mouse oocytes and embryos. Dev. Biol. 317: 36-45.

Wessel, G., S. D. Conner, and L. Berg. 2002. Cortical granule translocation is microfilament mediated and linked to meiotic maturation in the sea urchin oocyte. Development 129: 4315-4325.

Whitaker, M. 2006. Calcium at fertilization and in early development. Physiol. Rev. 86: 25-88.

Whitaker, M., and K. Swami. 1993. Lighting the fuse at fertilization. Development 117: 1-12.

Wilson, C. B. 1900. The habits and early development of Cerebratulus lacteus (Verrill): a contribution to physiological morphology. Q. J. Microsc. 43: 97-198.

Wu, A. T., P. Sutovsky. G. Manandhar, W. Xu. M. Katayama, B. N. Day, K. W. Park, Y. J. Yi, Y. W. Xi, R. S. Prather, et al. 2007. PAWP. a sperm-specific WW domain-binding protein, promotes meiotic resumption and pronuclear development during fertilization. J. Biol. Chenz. 282: 12164-12175.

Xia, G.-L., A. G. Byskov, and Y. C. Andersen. 1994. Cumulus cells secrete a meiosis-inducing substance by stimulation with forskolin and dibutyric cyclic adenosine monophosphate. Mol. Reprod. Dev. 39: 17-24.

Yamada, M., and Y. Isaji. 2011. Structural and functional changes linked to. and factors promoting, cytoplasmic maturation in mammalian oocytes. Reprod. Med. Biol. 2: 69-79.

Yamagata, Y., Y. Nakamura, N. Sugino. A. Harad, H. Takayama, S. Kashida, and H. Kato. 2002. Alterations in nitrate/nitrite and nitric oxide synthase in preovulatory follicules of gonadotropin-primed immature rat. Endocr. J. 49: 219-226.

Yamashita, M. 2000. Toward modeling of a general mechanism of MPF formation during oocyte maturation in vertebrates. Zool. Sci. 17: 841851.

Yi, J.-H., L. Lefievre. C. Gagnon, M. Anctil. and F. Dube. 2002. Increase of cAMP upon release from prophase arrest in surf clam oocytes. J. Cell. Sci. 115: 311-320.

Yoda, A., S. Oda, T. Shikano, Z. Kouchi, T. Awaji, H. Shirakawa, K. Kinoshita, and S. Miyazaki. 2004. Ca2+ oscillation-inducing phospholipase C zeta expressed in mouse eggs is accumulated to the pronucleus during egg activation. Dev. Biol. 268: 245-257.

Yoshida, M., N. Sensui, T. Inoue, M. Morisawa, and K. Mikoshiba. 1998. Role of two series of [Ca.sub.2+] oscillations in activation of ascidian eggs. Dec. Biol. 203: 122-133.

Yoshimura, Y., Y. Nakamura, M. Ando, M. Jinno. T. Oda, M. Karube, N. Koyama, and T. Nanno. 1992. Stimulatory role of cyclic adenosine monophosphate as a mediator of meiotic resumption in rabbit oocytes. Endocrinology 131. 351-356.

Zhang, M., Y. Tao, B. Zhou. H. Xie, F. Wang, L. Lei, L. Huo, Q. Sun, and G. Xia. 2005. Atrial natriuretic peptide inhibits the actions of FSH and forskolin in meiotic maturation of pig oocytes via different signalling pathways. J. Mol. Endocrinnl. 34: 459-472.

Zhang, Y.. Z. Zhang, X.-Y. Xu, X.-S. Li, M. Yu, A.-M. Yu, Z.-H. Zong, and B.-Z. Yu. 2008. Protein kinase A modulates Cdc25B activity during meiotic resumption of mouse oocytes. Dec. Dyn. 237: 3777-3786.

Zhou, H. M., and S. Y. Jin. 2007. [Ca.sup.2+] cascade and meiotic resumption of the caprine primary oocyte. Reprod. Domest. Anim. 42: 555-559.

Zuckerman, S. 1951. The number of oocytes in the mature ovary. Recent Prog. Horm. Res. 6: 63-109.

STEPHEN A. STRICKER*, CORY CLINE, AND DAVID GOODRICH Department of Biology. University of New Mexico, MSCO3 2020, Albuquerque, New Mexico 87131
COPYRIGHT 2013 University of Chicago Press
No portion of this article can be reproduced without the express written permission from the copyright holder.
Copyright 2013 Gale, Cengage Learning. All rights reserved.

Article Details
Printer friendly Cite/link Email Feedback
Author:Stricker, Stephen A.; Cline, Cory; Goodrich, David
Publication:The Biological Bulletin
Article Type:Report
Geographic Code:1USA
Date:Aug 1, 2013
Previous Article:Sperm nuclear basic proteins of tunicates and the origin of protamines.
Next Article:Species-Specificity of sperm motility activation and chemotaxis: a study on ascidian species.

Terms of use | Privacy policy | Copyright © 2019 Farlex, Inc. | Feedback | For webmasters