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A review on the physiology of Insulin like Growth Factor-I (IGF-I) peptide in bony fishes and its phylogenetic correlation in 30 different taxa of 14 families of teleosts.

Introduction

Fish are the first vertebrate group which has a complete system of ligands and receptors for the insulin / IGF family. Significance of the peptide group are due to its influence on some fundamental and vital metabolic and physiological process. IGF-I activity mainly its growth promoting functions mediated by the availability of growth hormone is well studied in fishes [108,25,26,130,15,171,170]. Influence of the peptide in growth occurs in a highly coordinated fashion & its regulatory significance has been established in many studies. IGF-I is distributed in several tissues and its expression is triggered by an assortment of factors, which is a hallmark of regulatory peptides. Review work on IGFs and various related peptides are available but information on IGF-I, its regulatory effects on growth, celldivision, adaptation, behavior, gonadal maturation and gamatogenesis etc are fragmentary.

Amongst the major review works, some are mentioned here viz, Yada [193] reviewed growth hormone and fish immune system. Evolutionary studies on IGFs , related peptides and their receptors have been carried out by many workers [115,78,177]. Sakamoto & McCormick [142] studied IGFs in osmoregulation. Role of IGFs and related peptides in gonadal development in fishes has been studied by Melamed et al [107] and Patino et al [125]. Otteson & Hitchcock at 2003 studied influence of IGFs in cell division and related functions. Moriyama in 2000 only reviewed the role of IGF-I in growth of fishes but its effect on several other functions was not available in literature. Navarro et al [115] reviewed Insulin, insulin-like growth factor-I and glucagon receptors extensively on the basis of binding characteristics, tissue distribution and structure. Reviews in relation to the regulation of growth by IGF-I and related peptides [37,135,114] are available in the literatures. Shved et al, 2005 & Eppler et al, 2005 studied expression patterns of IGF-I in various stages of development in bony fishes with limited emphasis on Oreochromis species.

A compilation of information relating to the intricate control cascades in molecular and cellular response of the peptide is lacking in the form of review work. Mechanisms and influence of the peptide are found to be much complex as evident from the most recent studies which are cited in the text accordingly.

There is a significant involvement of endocrine messengers in adaptation and evolution of complex traits [73,155,196] than any other physiological system. IGF-I peptide sequence in fishes also has tremendous evolutionary significance, and the phylogenetic correlation of the same in different fish taxa is therefore studied in one of the sections in this article. IGF-I has independent evolutionary history than that of the related peptides as insulin. McRory & Sherwood [105] have reported that insulin and IGF have maintained separate gene lineages in both vertebrate and protochordate evolution and, thus has a distinct evolutionary history of more than 600 million years. Studies [3,64] indicated that early in teleost evolution, around 320-350 million years ago, a whole genome duplication event took place and therefore the IGF system in teleosts is likely to be further complicated by the presence of gene paralogues. In salmonids further complication arise, as the teleost whole genome duplication was followed by an additional duplication event specifically within the salmonid lineage 25-100 million years ago [2]. It has been estimated that only 50% of the duplicated genes have subsequently been lost from the genome [10] with retained paralogues able to undergo subfunctionalisation leading to altered expression [92].

Distribution:

With reference to the versatile functions of the peptide, its distribution is found to be in wide spread in various tissues. The distribution as well as concentration among the tissues varies. Distribution of IGF-I, which has been mainly studied by localization of immunoreactivity, is observed in the muscle, pituitary gland, gonads, embryo, kidney, heart, spleen, various parts of G.I tract, calcified tissues , brain, the osmoregulatory organs during seawater adaptation and in liver with its highest expression. Free and bound IGF-I is present in the blood plasma .The peptide expression is also found to be highly regulated and many a times lifecycle and maturation stage dependent.

Yom et al [195] reported that while the IGF-I mRNA expression in Russian sturgeon (Acipenser gueldenstaedtii) differed amongst various tissues. Ng TB et al [117] observed IGF-I-like immunoreactivity was present in serum and at high levels in tilapia liver. Parrizas et al [132] observed that abundance of IGF-1 receptors in fish skeletal muscle in several species of salmonid fish and carp which is in contrast with the pattern observed in higher vertebrates. Banos et al [13] reported localization of IGF-I in the red muscle of fishes. Schmid et al [154] reported the occurrence of Insulin-like growth factor-I by in situ hybridization and immunohistochemical localisation in the ovary of a bony fish Oreochromis mossambicus.

Eppler et al [48] observed that IGF-I is distinctly located in the bony fish pituitary (Oreochromis niloticus) but in much less concentration than in liver. Kagawa et al [61] studied Immunocytochemical localization of IGF-I in the ovary of the red seabream, Pagrus major. Observations showed that the granulosa cell layer is the main site of IGF-I production. IGF-I may be involved in granulosa cell proliferation and differentiation. Gutierrez et al [58] reported Insulin and IGF-I binding and tyrosine kinase activity in fish heart and Moon et al [113] studied IGF-I binding in cardiac myocyte preparation from brown trout heart. Reinecke et al, [135] observed peptides related to insulin-like growth factor I in the gastro-entero-pancreatic system of bony and cartilaginous fish. Shamblott et al [149] observed the appearance of insulin-like growth factor mRNA in the liver and pyloric ceca of a teleost in response to exogenous growth hormone. Fukenstein et al [53] reported expression of IGF-I in eggs and embryos of Sparus aurata. In adult Odontesthes bonariensis it is revealed that IGF-I expressed ubiquitously with the highest mRNA levels in the liver, posterior intestine and brain [146].

Leibush et al [78] observed Insulin and insulin-like growth factor-I receptors in fish brain. Smith et al [163] localized insulin-like growth factor-I receptor binding sites in brain of the brown trout, Salmo trutta. Differential expression of IGF-I gene is observed by Sakamoto & Hirano[141] in the osmoregulatory organs during seawater adaptation of the salmonid fish. Developmentally regulated expression of IGF I and other related factors are observed in redbanded seabream, Pagrus auriga , and highest IGF-I transcripts found in liver (approximately 200-fold higher than head-kidney) [134]. According to Bautista et al [14] in the skeletal tissues of vertebrates, the IGFs are conserved and may be important regulators of osteogenesis. Tiago et al [172] observed in adult fish Sparus aurata, IGF-I gene expression in various soft tissues (highest levels in liver) and calcified tissues. IGF-1a and 1b during early post-hatching events (e.g. bone or muscle formation), while IGF-1c would be rather involved in early larvae formation but probably acts in concerted action with other isoforms at later stages. Shimizu et al [153] reported the distribution of free and protein-bound insulin-like growth factor-I (IGF-I) and IGF-binding proteins in plasma of bony fish (coho salmon, Oncorhynchus kisutch).

Therefore IGF-I regulatory peptide is found to be versatile in function and abundant in distribution with expression and regulation dependant on various physiological requirements to adapt successfully.

Seawater adaptation in fishes by IGF-I expression:

Osmoregulation is a fundamental problem in migratory fishes and they have developed efficient systems in order to maintain homeostasis and ionic balance of the body fluids. The physiology of osmoregulation calls for a variety of endocrine molecules which bring about changes in cellular and molecular level for efficient adaptation.

In many observations a variation in IGF-I expression during sea water adaptation has been reported. IGF-I influence osmoregulation mediated by GH and prolactin by and large effecting ion channel activity. McCormick et al in 1991 reported IGF-I as potential mediator of the action of GH in seawater adaptation in salmonids. Shepherd et al [151] reported that salinity acclimation affects the somatotropic axis in rainbow trout with IGF I and related peptides. Madsen et al [94] indicated that increased gill Na(+)-K(+)-ATPase activity is induced by sea water transfer, cortisol, GH, and IGF-I. McCormick SD [100] observed that IGF-I can increase salinity tolerance and gill Na+,K(+)-ATPase activity of Atlantic salmon. Tipsmark et al [175] in an important study reported that transfer of freshwater (FW)-acclimated Paralichthys lethostigma to sea water (SW) induced an increase in plasma osmolality and cortisol and a decrease in muscle water content, plasma insulin-like growth factor I (IGF-I) and hepatic IGF-I mRNA . Transfer of SW-acclimated flounder to FW reduced gill Na(+),K(+)-ATPase and Na(+),K(+),2Cl(-) cotransporter protein, increased plasma IGF-I, but did not alter hepatic IGF-I mRNA or plasma cortisol levels according to their experiment. Seidelin et al [147] reported that the stimulatory effects of IGF I and cortisol on Na+, K+-ATPase expression a vital component in osmoregulation, are additive and highly organ specific. Seidelin and Madsen [148] studied endocrine control of Na+,K+-ATPase and chloride cell development in brown trout (Salmo trutta) and observed that prolactin completely abolished the IGF-I stimulation of alpha-mRNA levels, resulting in a desensitisation of the gill tissue to IGF-I. Nilsen et al, [118] reported Gill IGF-I and IGF-I receptor (IGF-IR) mRNA levels increased in anadromous salmon during smoltification, with no changes observed in landlocked fish. Plasma IGF-I increased immediately in salt water in both catadromous and anadromous salmon, decreasing in both strains over a period of time in salt water. Cao et al [23] reported for the first time of a salinity-induced increase of GH-IGF-I circulating levels in Cypriniformes. Tipsmark et al [175] reported hyperosmoregulatory role of IGF-I in striped bass. Loss of Sea Water tolerance during short-term acid/Al exposure results from reductions in gill Na(+),K(+)-ATPase (NKA) activity and Na(+),K(+),2Cl(-) (NKCC), possibly mediated by decreases in plasma IGF-I and T3 (triiodo thyronin) [111].

Growth, Metamorphosis and Development:

In ectothermic teleost fishes growth process, is strongly influenced by environmental stimuli such as the changes in water temperature, photoperiod, food availability etc which along with the internal state of the animal is processed, integrated, and responded through hormonally mediated pathways, to trigger developmental processes such as hatching, metamorphosis (flatfishes, eels) or smoltification (salmonids), sexual maturation and spawning.

IGF-I influence growth in fish mediated by the endocrine cascade of GH. Studies have revealed the influence of IGF-I on cells ranging from osteblasts, chondrocytes, retinal cells etc, as well as muscle proteins. IGF-I signaling influence cell division in general as well as spermatogenesis, oogenesis and gamatogenesis by various mechanism and the effects are mediated by related molecules, cellular structures as gap junctions and various cascades. Much of these growth promoting actions and the target tissues will be reviewed in this section, cell division other then growth as in case of gametogenesis will be dealt separately. The protein is also found to effect apoptosis and cell size and tissue repair and these functions will be reviewd in other subsequent sections.

The liver production of the insulin-like growth factor-I (IGF-I) is a key factor in the endocrine control of body growth by a growth hormone. Growth promotion by IGF I has been studied extensively due to the possibility of economic exploitation in increasing consumable protein production. Experimental studies with a variety of IGFI peptides (synthetic and natural) and its counterparts are available. Tian et al [173] reported that E-peptides of rainbow trout pro-IGF-I possess mitogenic activity in heterologous systems. According to the study of Zhang et al [197] the recombinant mcIGF-I was more effective than recombinant mcGH to enhance the growth rate of juvenile tilapia. The recombinant mcIGF-I-treated fish revealed no significant changes of content of protein, lipid, ash and moisture in muscle. Codina et al [28] observed the role of IGF-I in both mitogenic and metabolic effects in trout muscle cells. Wargelius et al [185] and Nordgarden et al [120] reported that IGF-I stimulate vertebral growth and increase in bone density in a time dependant fashion in fishes. Mazurais et al [99] observed in Dicentrarchus labrax that the larvae group fed at the highest vitamin levels shows a temporal sequence of coordinated growth factor expression as the expression of bone morphometric protein (BMP-4) preceded by the expression of IGF-1, which stimulated the maturation of osteoblasts (revealed by high osteocalcin expression levels). Observations made by Patruno et al (2008) Dicentrarchus labrax conclusively proved that IGF-I is involved in the regulation of somatic growth in the sea bass. Hildahl et al [59] suggested that in addition to thyroid hormones, the GH-IGF-I system is involved in morphological transformations during metamorphosis and cranial remoulding in Atlantic halibut. Very et al [179] reported that somatostatinss regulate growth in an extra pituitary manner by reducing hepatic IGF-I biosynthesis and secretion.

Local upregulation of IGF-I takes place for switching to fast growth in Atlantic salmon skeletal muscle [22]. The plasma level of IGF-I and corresponding body size in the maturing adult chum salmon were two- to threefold than that of immature fish [121]. Plasma IGF-I levels are correlated to growth in Atlantic halibut, and affected by photoperiod treatment or compensatory growth during re-feeding. [63] The elevated plasma GH and reduced hepatic IGF-I mRNA levels observed in growth-retarded salmon suggested that stunted salmon may be GH resistant [40] more over hepatic GH resistance and diminished IGF-I production may be the central endocrine defects leading to growth retardation in stunted salmon. The incorporation of [35S] sulfate into cartilage has been shown to be stimulated by IGF-I [36,149]. McCormick et al [101] also reported that IGF-I has direct effects on coho salmon cartilage and may be an important regulator of growth in salmon and other teleosts and therefore stimulate growth. Raven et al 2008, described Paracrine stimulation of IGF-I by ectopic GH production in non-pituitary tissues is suggested by increased basal cartilage sulphation observed in the transgenic salmon. Cheng and Chen (1995) reported the synergism of GH and IGF-I in stimulation of sulphate uptake by branchial cartilage in teleost fishes.

Peterson et al, [130] demonstrated that feeding every other day has similar negative impacts on components of the GH-IGF-I axis as fasting and observed increase in SS-14 mRNA in the hypothalamus and pancreatic islets which suggests a role for SS-14 in modulating the GH-IGF-I axis in channel catfish. In fish growth by bone and cartilage formation T3 as well as IGF-I are important modulators of sulfated glycosaminoglycan synthesis in rainbow trout cartilage [167]. Negatu and Meier [115] observed that rhIGF-I stimulated [14C] glycine incorporation in muscles of teleost fisheas in a dose-dependent manner and that IGF-I may have a role in the regulation of growth in fish and that its activities are dose and time-of-day dependent. According to Shved et al [158] the impairing effects of estrogens on fish growth and reproductive functions may be due to the interaction between the sex steroid and the IGF-I system. Jo et al [66] reported the interplay between IGF-1 and cancer cell-derived clusterin durin metastasis, therefore demonstrating the level of complexity of IGF-I related activity with reference to cellular responses. Zygar et al [200] reported that IGF-1 produced by cone photoreceptors regulates rod progenitor proliferation in the teleost retina. Bouraoui et al, [17] proposed that Insulin growth factor-I stimulated adipocyte proliferation in culture.

Koriyama et al, (2007) studied effect of IGF-I in goldfish retinal ganglion cells during the early stage of optic nerve regeneration and reported that it is one of the most important regulatory peptide for controlling regeneration of retinal ganglion cells after optic nerve injury. Boucher & Hitchcock [18] observed Insulin-like growth factor-I binds in the inner plexiform layer and circumferential germinal zone in the retina of the goldfish. & reported that Insulin-related growth factors stimulate proliferation of retinal progenitors.

IGF-I and behavior in fishes:

Endocrine regulators influence animal behavior which is nothing but the adjustment between the internal physiology and the external environment of the animal. These adjustments are responded via the endocrine messenges. Like a typical endocrine modulator the IGF-I peptide influences various rythms in fishes and behavioural changes as well.

Vera Cruz and Brown [178] reported Lower social status depressed hepatic IGF-I levels while dominant status stimulated hepatic IGF-I production, possibly in response to inhibition of somatostatin release in the hypothalamus. A significant positive association was detected between the IGF-I mRNA expression of the dominant fish and the level of aggression (number of attacks) during the encounter. McCormick et al [102] reported control of smolting and related behavior in Atlantic salmon by temperature, photoperiod via endocrine rute (IGF-I). Shved N et al [157] reported that subordinate tilapia males showed a high IGF-I but a lower beta-luteinizing hormone expression, while in dominant males the opposite was found. Genetically based differences in hormone expression and regulation, particularly for IGF-I, are present in response to anthropogenic selection pressures in salmon and trout. Tymchuk et al [176] have observed altered expression of growth hormone / insulin-like growth factor I axis hormones in domesticated fish. Migration behavior is also found to regulated by IGF-I .The plasma level of IGF-I increased with elevation of the PG-axis activity prior to the initiation of spawning migration from the Bering Sea. [121].

IGF-I in Gamatogenesis, onset of puberty and embryonic development

The growth promoting effects of IGF-I in combination with other factors or in accordance with the internal environment, has an efficient cell signaling and modification action which can regulate events like onset of puberity, gamatogenesis, embryonic development etc.

Wang et al [184] reported a gonad specific subtype of IGFs and there fore its significance in gonadal development appears obvious. Paul et al [126] reported the involvement of IGF-I in the induction of oocyte maturation in Cyprinus carpio. The study suggests that PI3 kinase is an initial component of the signal transduction pathway which precedes MAP kinase, and MPF activation during IGF-I- and b-insulin-induced oocyte maturation in the major carp spercies. According to Maestro et al [98] the presence of insulin and IGF-I receptors in carp ovaries and the changes in percentage of binding throughout the reproductive cycle suggest that, in carp, the roles of insulin and IGF-I on the ovarian maturation stage. Aegerter et al [1] reported that IGF-I component is negatively correlated with the occurrence of morphological abnormalities observed at yolk-sac resorption, while the maternal stockpile of IGF-I (and related protein) mRNAs are positively correlated with embryonic survival.

Cyrino and Mulvaney [30] studied mitogenic activity of fetal insulin-like growth factor-I among other factors on brown bullhead catfish cells. IGF-I peptide regulates embryonic growth and development by promoting cell survival and cell cycle progression [143]. Insulin-like growth factor-I is a somatotropic signal that interacts with the PG-axis for gametogenesis and IGF-I from the GTH cells may act as auto/paracrine regulators of GTH cell proliferation and enhance GTH synthesis and release during puberty and reproduction, depending on the social status [157]. Baker et al [11] reported that Insulin-like growth factor I increases follicle-stimulating hormone (FSH). According to their experiment gonadotropin-releasing hormone-stimulated FSH release from coho salmon pituitary cells in vitro.

Nader et al [115] in an experiment observed that recombinant human insulin-like growth factor I stimulates all stages of 11-ketotestosterone-induced spermatogenesis in the Japanese eel, Anguilla japonica, in vitro. Furukuma et al [54] suggest that IGF-I itself directly stimulates synthesis and release of GTH early in gametogenesis in masu salmon, possibly acting as a metabolic signal that triggers the onset of puberty. The presence of insulin and IGF-I receptors in carp ovaries and the changes in percentage of binding throughout the reproductive cycle suggest that, in carp, the roles of insulin and IGF-I depend on the ovarian maturation stage. Vinas and Piferrer [181] observed stage-specific gene expression during fish spermatogenesis as determined by laser-capture microdissection and quantitative-PCR in sea bass (Dicentrarchus labrax) gonads. According to the study of Loir M. [85] IGF-I is a direct efficient stimulator of the proliferation of trout male germ cells, But Srivastava & Van der Kraak (1994) suggested that insulin, but not IGF-I, is capable of participating in the regulation of ovarian steroid biosynthesis.

Dubois et al [42] observed in a cartilaginous fish Squalus a stimulatory effect of insulin and IGF-I on DNA synthesis in premeiotic stages of proliferation of male germ cells. Kagawa et al [68] observed that in teleost, growth factors, such as IGF-I, are involved in the induction of germinal vesicle breakdown of oocytes. In the oocytes of red seabream, Pagrus major, IGF-I was the most potent inducer of GVBD in vitro. IGF-I appears to act directly on oocytes, and not via maturation-inducing hormone production, to induce germinal vesicle breakdown (GVBD). Patino et al [124] observed that IGF-I can regulate the abundance of heterologous and homologous gap junction which inturn influence course of development of oocyte maturational competence (OMC) in intact ovarian follicles of red seabream.

Lokman et al [87] reported that recombinant human IGF-I resulted in increased oocyte diameters, Anguilla australis, in vitro and indicates that hormones from both the reproductive and the metabolic axes in control of previtellogenic oocyte growth in a teleost fish. Weber et al [188,189,187,186] studied in vitro actions of insulin-like growth factor-I on ovarian follicle maturation in various coldwater and temperate habitat fishes. In Morone chrysops Weber and Sullivan [187] observed that Insulin-like growth factor-I induce oocyte maturational competence but not meiotic resumption. Weber & Sullivan [189] observerd that GtHmaturation-inducing steroid and IGF-I induce oocyte germinal vesicle breakdown in striped bass via phosphatidyl inositol 3-kinase activity. They also suggested the role of IGFs in maintenance of gap junctional communication required for maximal GtH and maturation-inducing steroid action. Chourasia & Joy [27] reported that recombinant IGF-I elicited a dose-dependent increase in germinal vesicle breakdown (GVBD), an index of oocyte maturation, in the catfish Heteropneustes fossilis. and rhIGF-I stimulated EH activity higher than GH or insulin. Glucose metabolism, the most vital of the metabolic pathways particularly have important regulation via IGF-I. Insulin and IGF-I increased the mRNA levels of GLUT4 in myoblasts and myotubes of a primary culture of trout muscle cells. On the other hand, IGFI appeared to be more potent than insulin in stimulating GLUT1 expression, particularly at the myoblast stage [34].

Davis et al [32] suggested that down-regulation of the GH/IGF-I axis stimulates vitelogenine production primarily through activation of ER alpha and, thus shifting energy from somatic growth towards vitellogenesis in liver. The observations of Monette et al, [111] indicated that smolt development and Sea Water tolerance are compromised by short-term exposure to acid/Aluminum in the absence of detectable impacts on Fresh Water ion regulation. Loir & Le Gac [86] studied Insulin-like growth factor-I and -II binding and their action on DNA synthesis in rainbow trout spermatogonia and spermatocytes. They found in vitro, IGFs stimulate DNA synthesis of trout male germ cells by interacting directly with these cells through one IGF receptor. Fukenstein [53] observed that IGF-I transcripts are present in fish Sparus aurata during embryogenesis, which is probably of maternal origin. Duguay et al [46] indicate that IGF-I is expressed during embryonic development of fish, and that most tissues are capable of IGF-I mRNA production. Weil et al [190] suggested a putative role of IGF-I and GnRH as a link between growth and puberty.

Regulation and Expression of IGF I:

Hormones and hormone like entities exert dynamic action on various physiological or cellular functions and therefore controlled by a number of switch-on and switch-off commands. Occurence of other regulatory molecules and factors (peptides as GH, somatolactin, somatostatin, ghrelin etc, steroids as Cortisol, Estrogen and the thyroid hormones) influence IGF-I expression. Various physicochemical factors of the immediate environment, photo period, growth stage, nutrition level, stress condition , sex of the fish etc influence the regulation of expression of IGF-I peptide as well.

Duguay et al [44] demonstrated that the expression of IGF-I and IGF-II is highly regulated in teleosts and suggest that they play distinct roles during growth and development. Many workers [81,6,7] described the IGF-I expression pattern with respect to growth stage and developmental stage but Maestro et al [98] reported the appearance of insulin and insulin-like growth factor-I (IGF-I) receptors throughout the ontogeny of brown trout (Salmo trutta fario). Ponce et al [134] studied the developmentally regulated expression of IGF I and other related factors and observed that IGF-I reached the highest expression levels at 18 days after hatching (11.6-fold higher than 1 day after hatching) in redbanded seabream, Pagrus auriga. Hu et al [62] reported that XBP-1, a key regulator of unfolded protein response, activates transcription of IGF1 in zebrafish embryonic cell line. Montserrat et al [112] observed in myocyte culture of gilthead sea bream the expression of functional IGF-I receptors that increase in number as they differentiate in vitro. They hav reported that IGF signaling transduction through IGF-I receptors stimulates the MAPK and Akt pathways, depending on the development stage of the muscle cell culture.

Kulik et al [76] reported that (Hepatocyte nuclear factor 1) HNF-1 may be an important regulator of IGF-I gene expression in animals inclding fishes since the sequence of the HNF-1 binding site is conserved in all mammalian, avian, and amphibian species from which the IGF-I promoter sequences have been derived to date.

Shamblott et al [149] reported that in primary hepatocyte culture, IGF I and IGF II mRNA levels increased in a GH dose-dependent fashion. Funkenstein et al [52] reported that Growth hormone increases plasma levels of insulin-like growth factor (IGF-I) in a teleost, the gilthead seabream (Sparus aurata). Vong et al [182] reported differential regulation of expression of IGF I and II by GH in Cyprinus carpio. Duan et al. [41] found that GH and somatolactin stimulated liver IGF-ImRNA expression in sockeye and coho salmon. Hagemeister & Sheridan [59] reported that somatostatin inhibits hepatic growth hormone receptor and insulin-like growth factor I mRNA expression by activating the ERK and PI3K signaling pathways. Klein & Sheridan [75] reported that somatostatin alter growth via both direct and indirect actions, including inhibiting growth hormone release at the pituitary, decreasing hepatic GH sensitivity, and lowering plasma IGF-I levels. Very & Sheridan [180] reported inhibition of insulin-like growth factor-I receptor expression in the gill of a teleost fish (Oncorhynchus mykiss) by Somatostatin. Fox et al [50] reported role of ghrelin in regulation of IGF-I and observed that tilapia ghrelins stimulate primarily GH release through the GHS receptor. Stimulation of hepatic expression of IGF-I and GHR suggests metabolic roles of ghrelin in tilapia.

Steroids likewise the regulatory peptides significantly influence cellular and metabolic activities. Riley et al [137] reported multiple observations on the effect of steroids. Kelley et al [72] observed a strong relationship between elevated serum cortisol concentrations and the presence of IGFBPs in experimental fish samples, and reported the utility of serum IGFBP measurement to serve as an effective indicator (marker) of catabolic condition in fishes. According to Shved N et al [157] in developing bony fish tilapia (Estrogen) EE2 treatment resulted in significant changes of ER alpha and IGF-I expression in ovaries and testis, which suggests that the estrogens interact not only with the endocrine but also with the autocrine/paracrine part of the IGF-I system. Shved et al [158] reported evidence that EE2 at environmentally relevant concentrations is able to interfere with the GH/IGF-I system in bony fish. Suzuki et al [166] observed marked increase in mRNA expressions of IGF-I as well as osteoclastic and osteoblastic activities in 17beta-estradiol (E2) treated scales of goldfish and wrasse. This study also reported the effect of an allogenic Monohydroxylated polycyclic aromatic hydrocarbons which is found to inhibit both osteoclastic and osteoblastic activities in teleost scales. In an interesting study Lerner et al [79] observed in fresh water salmon fishes that, estrogens E2 reduced sodium potassium-activated adenosine triphosphatase activity as well as plasma levels of insulin-like growth factor I. The study also indicated that exposure of anadromous salmonids to environmental estrogens heightens sensitivity to external stressors, impairs ion regulation in both FW (fresh water) and SW (salt water), and disrupts endocrine pathways critical for smolt development. Davis et al [32] indicate that o,p'-DDE and heptachlor (allogenous endocrine disruptors) have varying temporal and dose effects on modulation of vitellogenin Vg and the GH/IGF-I axis that are distinct from 17beta-estradiol E(2) in the tilapia, Oreochromis mossambicus. Schmid et al [144] reported that thyroid hormone (T3) stimulates hepatic IGF-I mRNA expression in a bony fish, tilapia Oreochromis mossambicus, in vitro and in vivo.

Peddu et al [128] studied pre- and postprandial effects on ghrelin signaling in the brain and on the GH/IGF-I axis in the Mozambique tilapia (Oreochromis mossambicus) and observed that postprandial levels of plasma IGF-I were elevated in both fed and fasted tilapia and Riley et al, [137] demonstrated that fasting significantly reduced plasma levels of IGF-I.

Temperature seems to promote growth through IGF1 secretion by the liver. Luckenbach et al [88] reported that temperature affects insulin-like growth factor I. According to Gabillard et al [55] in rainbow trout that environmental temperature may, independently of nutritional status, directly stimulate plasma growth hormone (GH) that is recognised as being an insulin-like growth factor (IGF) system regulator. Taylor et al [169] reported that in maturing female rainbow trout under natural photoperiod typically expressed higher circulating IGF-I levels than those that remained immature and may reflect a greater opportunity for IGF-I to act on the pituitary to stimulate gonadotropin production. Shimizu et al [152] observed that IGF-I adjusts its basal levels to the long-term nutritional status and is less responsive to acute nutritional input but IGFBPs maintain their sensitivity to food intake. But Fox et al [50] reported that four weeks of fasting did not affect plasma GH levels, although plasma IGF-I and glucose were reduced significantly. Saera-Vila et al (2009) studied the dynamics of liver GH/IGF axis and selected stress markers in juvenile gilthead sea bream (Sparus aurata) exposed to acute confinement and observed consistent decrease in circulating levels of insulin-like growth factor-I (IGF-I). Ayson &Takemura [7] observed IGF-I expression do not seem to follow a rhythm according to light and dark cycles wheras Meton et al [108] reported that liver insulin-like growth factor-I mRNA shows diurnal variations in gilthead sea bream(Sparus aurata).

Cote et al [29] reported that both environment and sex have major impacts on the expression of mRNA for two key genes involved in the physiological pathway for growth GHR and IGF-1. The study also demonstrated for the first time, at least in fish, genotype-by-environment interaction at the level of individual gene transcription. This work contributes significantly to ongoing efforts towards documenting environmentally and sexually induced variance of gene activity and understanding the resulting phenotypes. Davis et al [31] reported hepatic expression as well as plasma IGF-I levels were higher in male Oreochromis mossambicus than in females reflecting greater growth rate in male. Hypophysectomy did not affect liver IGF-I mRNA levels in the euryhaline teleost, the tilapia, Oreochromis mossambicus. [20]. IGF-I peptide not only is regulated by various measure but also excert its effect on expression of some other molecules which again signifies ites importance. Rousseau et al [138] reported the long-term inhibitory effects of somatostatin and insulin-like growth factor 1 on growth hormone release by serum-free primary culture of pituitary cells from european eel (Anguilla anguilla).

Cellular and Molecular response to IGF I activity:

IGF-I activity and its effect on various fish species has revealed much of its functions in fish physiology. This section reviews various experimental observations by several workers on the some aspects of cellular and molecular response to IGF-I activity as in cellcycle regulation, apoptosis and metastasis as well as on immune response.

Madsen et al, [95] reported that expression of cystic fibrosis transmembrane conductance regulator (CFTR) remains unaffected by IGF-I. Perez et al [129] observed the effect of human recombinant IGF-I in GH regulation in fishes and reported the participation of IGFs on the inhibitory component of fish GH regulation n a dose dependant manner. Melamed et al [106] suggest that estradiol and IGF-I, both generated from cells other than the somatotrophs, may exert antiapoptotic effects and thus possibly control the size of this somatotroph cells. Wood & van der Kraak G. [191] studied the inhibition of apoptosis in vitellogenic ovarian follicles of rainbow trout (Oncorhynchus mykiss) by various factors and reported no apparent affect of IGFs. Deane et al [33] reported that upon exposure to IGF-1 it was found that HSP70 expression remained unchanged in fibroblasts but was significantly decreased in macrophages at exposure concentrations of 1-10ng/ml. In an interesting study Siri et al [156] observed inhibition of human breast cancer cell (MBA-MD-231) invasion by the Ea4-peptide of rainbow trout pro-IGF-I.

Response to the immune system via regulatory peptides as IGFs is an important problem in physiology. In a study Yada [194] has reported that IGF-I stimulates non-specific immune functions In fish. Yada [193] reported the experimental results of in-vivo intraperitoneal injection of sIGF-I and subsequent increase of plasma lysozyme, which indicate that IGF-I stimulates non-specific immune functions in fish. Gutierrez et al [58] observed that receptor tyrosine kinase activity could be stimulated in a dose-dependent manner by insulin and IGF-I. Berwert et al [16] studied ontogeny of IGF-1 and the classical islet hormones in the turbot, Scophthalmus maximus. They observed Islet-derived IGF-1 might inhibit the regulation of INS secretion in a paracrine manner and may be highly involved in growth-promoting processes. Lin & Ge [82] observed that insulin-like growth factor I,(IGF-I) exhibited distinct effects on the expression of the three genes FSHbeta (fshb), LHbeta (lhb), and GH (gh) in zebra fish. Picha et al [131] reported that IGF-I influence GH activity. Codina et al [28] reported that IGFs exert mitogenic and metabolic effects in trout muscle cells though the same MAPK and PI3K/Akt signaling pathways .According to another study by Picha et al [131] endocrine and paracrine/autocrine components of the GH-IGF axis, namely IGF 1, IGF 2, and ghr1 and ghr2, may be involved in compensatory growth responses in a hybrid striped bass (HSB, Morone chrysops X Morone saxatilis), with several of the gene expression variables exceeding normal levels during CG. Experiments by Skyrud et al, [162] suggest that recombinant hIGF-1 does not stimulate growth, but that in high dosages causes profound insulin-like effects in brook trout resulting in hypoglycemia and hypoaminoacidemia. Study by Cao et al [24] revealed that the level of prepro IGF-I mRNA is increased 6-fold in liver RNA isolated from Oncorhynchus kisutch (coho salmon) injected with bovine GH, as compared to untreated controls. Inhibition of IGF-I. According to many workers [154,35,133] in fish serum and extracellular fluids IGF-I is bound to specific binding proteins (IGFBPs) (2-4) which modulate its biological activity. According to an experiment conducted by Duan [38] when over expressed and added exogenously to zebra fish and mammalian cells, IGFBP-2 inhibited IGF-I and serum-stimulated cell proliferation and DNA synthesis. IGFBP-1 is strongly up-regulated under catabolic circumstances, and it plays an important physiological role by sequestering IGF peptides to inhibit energy-expensive growth until conditions are more favorable. Alternative splicing of IGF mRNA also occurs in salmonid fish [37]. According to Wallis et al [183] polymerase chain reaction analysis suggests the presence of two structurally different salmonid IGF-I genes with the potential for multiple splicing alternatives of the IGFI transcript. Lynn et al [89] studied the seasonal and sex-specific mRNA levels of IGF-Ib in adult yellow perch (Perca flavescens) showed significant effects of season and sex on adult yellow perch endocrine physiology. Monette [111] reported that exposure to toxicants like Acid/Aluminium resulted in decreased plasma insulin-like growth factor (IGF-I) in Atlantic salmon (Salmo salar). Gray et al [56] studied the roles of growth hormone, hepatic growth hormone receptors and insulin-like growth factor-I in growth regulation in the gobiid teleost, Gillichthys mirabilis. Anderson [5] studied the presence of insulin-like growth factor-I (IGF-I)-related molecules and IGF-binding factors in blood from golden perch, Macquaria ambigua, an Australian native freshwater fish. Kelley et al [71] observed that IGF-I activity is influenced by insulin in ectothermic vertebrate, Gillichthys mirabilis. Studies by Madsen & Bern [93] showed that rbIGF-I stimulates gill Na(+),K(+)-ATPase directly; an ability that may depend on priming by endogenous or exogenous GH which supports the role of IGF-I as an endocrine mediator for GH action during parr-smolt transformation. According to Plisetskaya et al [133] preparations from salmon brain stimulated the [35S] sulfate uptake into salmon branchial cartilage with a potency comparable to pure mammalian or salmon insulins but lower than that of mammalian insulin-like growth factor (IGF-I). Duan et al [39] suggested that food deprivation primarily reduces IGF-I mRNA expression in the liver which results, most probably, in a decline in systemic IGF-I levels and consequently leads to the retarded growth of salmon.

Shamblott M.J, [150] observed that at least 1 form of IGF I and IGF II mRNA are present at both developmental stages in all tissues examined; and all 5 IGF mRNA forms are present at their highest levels in the liver (p < 0.05); moreover adults have significantly higher IGF mRNA levels than juveniles in the liver (p = 0.0047).

Using organotypic slice cultures of differentiated teleost fish retinal tissue, Mack et al [91] found that insulin and insulin-like growth factor I (IGF-I) stimulate proliferation of rod precursor cells and insulin and the related IGF-I can influence the regulation of neuronal cell division. Anderson et al [4] observed that addition of insulin-like growth factor-I to the medium accelerates the process of neuronal differentiation from the caudalmost precursor cells of adult teleost in vitro. Salmon have been shown to express alternatively spliced IGF-I mRNA transcripts coding for four different IGF-I prohormones and Differential expression and hormonal regulation of alternatively spliced IGF-I mRNA transcripts in salmon was studied by Duguay et al [45], which report that The increased IGF-I mRNA levels observed in gill tissue during smoltification suggest that various factors, in addition to GH, may regulate IGF-I expression.

McRory & Sherwood [104] observed that in the Thai Catfish express two forms of insulin-like growth factor-I (IGF-I) in the brain. Ubiquitous IGF-I and brain-specific IGF-I. According to the strudy of Brian et al. [20] homologous pituitary hormones tPRL177(Prolactin) and tGH promote growth and alter levels of liver IGF-I in Hx adult animals (teleost, Oreochromis mossambicus). Duan et al (1995) observed that the elevated plasma GH and reduced hepatic IGF-I mRNA levels in growth-retarded salmon which suggested that stunted salmon may be GH resistant. Hepatic GH resistance and diminished IGF-I production may be the central endocrine defects leading to growth retardation in stunted salmon. A decrease in IGF-I immunoreactivity was observed by Perez et al [129] in a marine teleost, the gilthead sea bream (Sparus aurata) fed with high protein diet and probably it is a part of the mechanism that diminishes feed utilization for growth at high feeding level. Shved et al (2007) reported that developmental estrogen treatment brings about persistent impairment of GH/IGF-I expression in fish via inhibition of pituitary GH and directly by suppression of local IGF-I in organ-specific cells.

Evolutionary significance of IGF-I peptide in fishes:

Vital peptides by convention display high degree of conservation in evolutionary timeframe , therefore presents them selves as an important tool for the assessment of significant events such as genome duplication, gene paralogue formation etc in the evolutionary history of the peptide. IGF-I in this regard is a suitable candidate for various evolutionary study, the results of which can be inferred to understand the phylogenetic correlation among the caqndidate taxa from which the peptides have been isolated.

The sequences of the exons encoding the mature insulin and IGF peptides are highly conserved among vertebrate species, and IGF-I-like molecules are found in species whose origins extend back as much as 550 million years [80]. Studies by Upton [177] indicated that the IGF-I proteins appear to have been remarkably conserved in both structure and in vitro action during vertebrate radiation. Experimental data observed by Bauchat

et al (2001) clearly suggested that the IGFBP molecule an imported subunit in the igf-I system is structurally and functionally conserved in evolutionarily ancient vertebrate species such as bony fish.

Greene and Chen [57] suggested towards the conservation of the role played by insulin like growth factor peptides (IGF-I and IGF-II) during embryonic development in vertebrates. IGF-I receptors in lamprey tissues are very similar to mammalian IGF-I receptors confirming known evolutionary conservatism of IGF receptor system [77]. In an attempt to identify genes with a potential influence on growth and development in salmonid species Moghadam et al [110] suggested a tight association between the IGF1, MYF5 and MYF6 genes and reported of a more ancient polyploidization event that occurred deep in the ray-finned fish lineage.

Duguay et al [45] studied the Divergence of insulin-like growth factors I and II in the elasmobranch Squalus acanthias and observed that the prototypical IGF molecule duplicated and diverged in an ancestor of the extant gnathostomes. According to Reinecke et al [136] in most bony fish species with the exception of Cottus, IGF-1 and insulin display a distinct cellular distribution, similar to that of mammals which may indicate that the branching of IGF-1 and insulin has occurred at the phylogenetic level of bony fish.

In the present study a review on the physiology of the peptide IGF-I and its evolutionary relationship in various fish taxa has been carried out. A related peptide Insulin-like growth factor II was studied by O'Neill et al [109] with similar considerations of phylogenetic correlation among various fish taxa and Josep et al [67] studied the receptor phylogeny of Insulin, IGF-I and II. For the present study peptide sequences of 30 different bony fish species were retrived from the GENBANK (www.ncbi.nlm.nih.gov/). Some of the sequences are conceptual translation of the cloned gene IGF-I. An account of the peptide sequences with that of the fish species is given in the Table 1.

The sequences were studied in order to infer the phylogenetic correlation by a computational evolutionary biology freeware named MEGA,4 [c].

The peptide sequences were aligned by the BLOSUM program inbuilt to MEGA,4.

The aligned sequences were subjected to three different computational models described as Neighbor-Joining method, Maximum Parsimony method and UPGMA method. The text also describes statistical analysis of the observation as Tajma, s neutrality test.

Figure 1 depicts the evolutionary history of the peptide sequence using the Neighbor-Joining method [140]. The optimal tree with the sum of branch length =1.01031246 is shown. The percentage of replicate trees in which the associated taxa clustered together in the bootstrap test (500 replicates) are shown next to the branches [49]. The tree is drawn to scale, with branch lengths in the same units as those of the evolutionary distances used to infer the phylogenetic tree. The evolutionary distances were computed using the Poisson correction method [199] and are in the units of the number of amino acid substitutions per site. All positions containing gaps and missing data were eliminated from the dataset (Complete deletion option). There were a total of 16 positions in the final dataset. Phylogenetic analyses were conducted in MEGA4 [168].

[FIGURE 1 OMITTED]

Whereas Figure 2 is the phylogenetic tree of the peptide sequence using Maximum Parsimony method [47]. Tree #1 out of 500 most parsimonious trees (length = 15) is shown. The consistency index is (0.800000), the retention index is (0.960000), and the composite index is 0.896000 (0.768000) for all sites and parsimony-informative sites (in parentheses).

The percentage of replicate trees in which the associated taxa clustered together in the bootstrap test (500 replicates) are shown next to the branches [49] The MP tree was obtained using the Close-Neighbor-Interchange algorithm [116] with search level 3 [49,116] in which the initial trees were obtained with the random addition of sequences (10 replicates).

All positions containing gaps and missing data were eliminated from the dataset (Complete Deletion option). There were a total of 16 positions in the final dataset, out of which 2 were parsimony informative.

[FIGURE 1 OMITTED]

[FIGURE 2 OMITTED]

[FIGURE 3 OMITTED]

The evolutionary history of 30 different fish taxa is inferred using the UPGMA method in Figure 3 [164]. The optimal tree with the sum of branch length = 0.96551482 is shown. The percentage of replicate trees in which the associated taxa clustered together in the bootstrap test (500 replicates) are shown next to the branches [49].

The tree is drawn to scale, with branch lengths in the same units as those of the evolutionary distances used to infer the phylogenetic tree. The evolutionary distances were computed using the Poisson correction method [199] and are in the units of the number of amino acid substitutions per site. All positions containing gaps and missing data were eliminated from the dataset (Complete deletion option). There were a total of 16 positions in the final dataset.

The Tajima test statistic (Table 2) was estimated using MEGA4. All positions containing gaps and missing data were eliminated from the dataset (complete deletion option).

The abbreviations used are as follows:

m = Number of sites,

S = Number of segregating sites,

Ps = S/m,

[THETA] = Ps/a1 and

[PI] = Nucleotide diversity,

D = The Tajima test statistic.

Conclusion:

Messenger molecules are celebrated as the epicenter molecules in studies relating to physiology. Review on a cluster of related regulatory molecules projects the informations on various aspects in a diffused manner and readers often fail to make out the individual context. The need is more so when structure, function as well as regulation of the molecules share much homology as in the case of Insulin, Insulin Like Growth Factor-I, II etc and their respective receptors.

Evolutionary changes in endocrine regulation are thought to be an especially important mechanism by which entire suites of traits evolve in a coordinated manner in response to environmental change, either via selection on heritable, fitness-related, individual variation or through adaptive phenotypic plasticity [43,196]. Therefore phylogenetic correlation of relatedness exclusive for single endocrine molecule in a large group of taxons in a systematic unit (as in a class) is important to study the evolutionary pattern of the molecule and to infer significant incidence as duplication, selection, rearrangement etc in course of evolution of the molecule.

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Corresponding Author

Surajit Debnath, Lecturer, Department of Medical Laboratory Technology Women,s Polytechnic, Govt. of Tripura Hapania, P.O:Amtali, Tripura (W) PIN:799130 India Ph/FAX:91-381-2376814 0-9862015352 (M), Email: surajit03@yahoo.co.in

Surajit Debnath

Lecturer, Department of Medical Laboratory Technology Women,s Polytechnic, Govt. of Tripura Hapania, P.O: Amtali, Tripura (W) PIN:799130 India,

Surajit Debnath: A Review on the physiology of Insulin like Growth Factor-I (IGF-I) peptide in bony fishes and its phylogenetic correlation in 30 different taxa of 14 families of teleosts.
Table 1: Insulin like Growth Factor I (IGF-I) in some bony fish
species.

Name of The fish            Family             Distribution

Danio rerio                 Cyprinidae         Tropical
Salmo salar                 Salmonidae         Temperate
Oncorhynchus mykiss         Salmonidae         Subtropical
Cyprinus carpio             Cyprinidae         Subtropical
Oreochromis mossambicus     Cichlidae          Tropical
Carassins auratus           Cyprinidae         Subtropical
Oreochromis niloticus       Cichlidae          Tropical
Ictalurus punctatus         Ictaluridae        Subtropical
Ctenopharyngodon idella     Cyprinidae         Tropical
Paralichthys olivacens      Paralichthyidae    Subtropical
Dicentrarchus labrax        Moronidae          Subtropical
Epinephelus coioides        Serranidae         Subtropical
Cynoglossus semilaevis      Cynoglossidae      Subtropical
Oncorhynchus keta           Salmonidae         Temperate
Pimephales promelas         Cyprinidae 2       Subtropical
Rhabdosargus sarba          Sparidae           Tropical
Psetta maxima               Scophthalmida      Temperate
Umbrina cirrosa             Sciaenidae         Subtropical
Sparus aurata               Sparidae           Subtropical
Dentex dentex               Sparidae           Subtropical
Cirrhinus molitorella       Cyprinidae         Tropical
Cottus kazika               Cottidae           Temperate
Acipenser baerii            Acipenseridae      Boreal
Paralichthys adspersus      Paralichthyidae    Subtropical
Spinibarbus sinensis        Cyprinidae         Subtropical
Procypris rabaudi           Cyprinidae         Subtropical
Mugil cephalus              Mugilidae          Subtropical
Megalobrama amblycephala    Cyprinidae         Temperate
Micropterus salmoides       Centrarchidae      Subtropical
Myxocyprinus asiaticus      Catostomidae       Subtropical

Name of The fish            Habitat                        Locus/
                                                           Accession

Danio rerio                 Freshwater                     NP_571900
Salmo salar                 Freshwater; brackish; marine   NP_001117095
Oncorhynchus mykiss         Freshwater; brackish; marine   NP_001118168
Cyprinus carpio             Freshwater; brackish           AAP78926
Oreochromis mossambicus     Freshwater                     CAA77264
Carassins auratus           Freshwater                     ABG75920
Oreochromis niloticus       Freshwater                     ABY88872
Ictalurus punctatus         Freshwater                     AAQ56592
Ctenopharyngodon idella     Freshwater                     ABU40947
Paralichthys olivacens      Marine                         AAB94052
Dicentrarchus labrax        Freshwater; brackish; marine   AAV67967
Epinephelus coioides        Brackish; marine               AAV34198
Cynoglossus semilaevis      Marine                         ACM43291
Oncorhynchus keta           Freshwater; brackish; marine   AAB31275
Pimephales promelas         Demersal; freshwater           AAT02176
Rhabdosargus sarba          Brackish; marine               AAT48996
Psetta maxima               Brackish; marine               ACL14947
Umbrina cirrosa             Brackish; marine.              AAY21628
Sparus aurata               Marine                         ABQ52656
Dentex dentex               Marine                         ABD74624
Cirrhinus molitorella       Freshwater;                    AAY21902
Cottus kazika               Freshwater; brackish; marine   BAC07249
Acipenser baerii            Freshwater                     ACJ60678
Paralichthys adspersus      Marine                         ABS52702
Spinibarbus sinensis        Freshwater                     ABE03747
Procypris rabaudi           Freshwater                     ACF17426
Mugil cephalus              Freshwater; brackish; marine   AAR06903
Megalobrama amblycephala    Freshwater                     AAK16727
Micropterus salmoides       Freshwater                     ABG57072
Myxocyprinus asiaticus      Freshwater                     ABH12114

Name of The fish            Amino Acid         GI
                            Chain Length

Danio rerio                 161 aa             18858887
Salmo salar                 176 aa             185135977
Oncorhynchus mykiss         176 aa             185135756
Cyprinus carpio             178 aa             32306478
Oreochromis mossambicus     126 aa             4376056
Carassins auratus           161 aa             110559329
Oreochromis niloticus       182 aa             166716484
Ictalurus punctatus         159 aa             34016863
Ctenopharyngodon idella     161 aa             155965940
Paralichthys olivacens      185 aa             2736077
Dicentrarchus labrax        186 aa             55925786
Epinephelus coioides        186 aa             54399798
Cynoglossus semilaevis      187 aa             222092509
Oncorhynchus keta           79 aa              13366272
Pimephales promelas         161 aa             46811844
Rhabdosargus sarba          67 aa              49037298
Psetta maxima               151 aa             219524765
Umbrina cirrosa             186 aa             62912031
Sparus aurata               182 aa             147945602
Dentex dentex               173 aa             89513591
Cirrhinus molitorella       161 aa             62913803
Cottus kazika               183 aa             22128346
Acipenser baerii            160 aa             213990591
Paralichthys adspersus      185 aa             153861678
Spinibarbus sinensis        161 aa             90994362
Procypris rabaudi           161 aa             193247174
Mugil cephalus              186 aa             37993618
Megalobrama amblycephala    161 aa             13249283
Micropterus salmoides       186aa              110270472
Myxocyprinus asiaticus      161aa              111660993

Name of The fish            Reference

Danio rerio                 Lin et al. [82]
Salmo salar                 Bower et al. [22]
Oncorhynchus mykiss         Shamblott et al. [150]
Cyprinus carpio             Vong et al. [182]
Oreochromis mossambicus     Schmid et al. [145]
Carassins auratus           Liu et al. [84]
Oreochromis niloticus       Wang et al. [184]
Ictalurus punctatus         Clay et al.
Ctenopharyngodon idella     Brown et al. [21]
Paralichthys olivacens      Kim et al. [74]
Dicentrarchus labrax        Terova et al. [170]
Epinephelus coioides        Bangcaya et al. [14]
Cynoglossus semilaevis      Ji et al. [65]
Oncorhynchus keta           Kavsan et al. [68]
Pimephales promelas         Filby et al., [51]
Rhabdosargus sarba          Deane et al, [33]
Psetta maxima               Xing et al [192]
Umbrina cirrosa             Patruno et al., [127]
Sparus aurata               Duguay et al, [44]
Dentex dentex               Bermejo-Nogales et al, [17]
Cirrhinus molitorella       Zhang et al, [198]
Cottus kazika               Inoue et al, [63]
Acipenser baerii            Hu et al, [61]
Paralichthys adspersus      Fuentes et al, [51]
Spinibarbus sinensis        Huang et al, [60]
Procypris rabaudi           Li et al, [81]
Mugil cephalus              Nocillado et al, [119]
Megalobrama amblycephala    Bai et al, [9]
Micropterus salmoides       Li et al, [83]
Myxocyprinus asiaticus      Zheng et al, [198]

Table 2: Tajima's Neutrality Test for IGF-I amino acid sequence in
30 taxa of bony fishes.

m       S    Ps           [THETA]      [PI]         D

30      o    0.625000     0.1577762    0.109626     -0.966328
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Title Annotation:Original Article
Author:Debnath, Surajit
Publication:Advances in Environmental Biology
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Geographic Code:5ANGU
Date:Jan 1, 2011
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