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Screening of genes specifically expressed in males of Fenneropenaeus chinensis and their potential as sex markers.

1. Introduction

The existence of sex dimorphism is a very common phenomenon in crustaceans. A number of crustacean species exhibit bimodal growth patterns in which males exhibit superior growth to females or vice versa [1]. Female penaeid shrimps usually show superior growth than males when they reach maturation. For example, females exhibit approximately 10-20% higher growth rate than males in Penaeus monodon [2]. Therefore, culture of monosex population is a good way to raise the production of cultured species.

Understanding the mechanism of sex determination and sex differentiation will facilitate the development of molecular tools for producing monosex populations in crustacean species [3]. However, little information about sex determination cascades and sexdiagnostic markers is available in penaeid shrimp [4]. A ZW sex determination system in penaeid shrimp was proposed based on the data that the progeny of interspecific hybridization between females of P. monodon and males of Penaeus esculentus had a higher proportion (86%) of males than females [5]. The following reports that female specific-markers were found in the female genetic linkage maps for Penaeus japonicus [6]and Litopenaeus vannamei [7] and that the induced triploids P. japonicus were always female [8,9] also support the previous hypothesis that a ZW sex determination mechanism might exist in penaeid shrimp. However, in the induced triploid population of F. chinensis, although more female triploid shrimp were obtained, males still existed in the triploid population [10]. The existence of male offspring in the triploid Chinese shrimp might be caused by the polar body I induction, which also brought male triploid offspring in Marsupenaeus japonicus [11]. This phenomenon made the sex determination system of penaeid shrimp more complicated than simple X/Y or Z/W systems. A recent report showed that no apparent sex bivalent was observed in male F. chinensis through synaptonemal complex (SC) analysis, which suggested that the male shrimp might be the homogametic sex [12]. Our previous studies have demonstrated that the sex determination of penaeid shrimp might adopt a similar mechanism with that in Drosophila [13]. However, the current information still limits our understanding on the sex determination mechanism of penaeid shrimp.

Development of sex markers can facilitate the development of monosex production techniques. Attempts have been made to seek sex markers on genomic DNA and RNA levels. Although it failed to isolate sex-related markers from genomic DNA through bulked segregant analysis (BSA) and AFLP method, it worked at the RNA level through RAPPCR between testes and ovaries in P. monodon [4]. A sex-related cDNA fragment was isolated from F. chinensis through DDRT [14]. Sex-related genes expressed in the ovary and testis of P. monodon were identified by EST approach [15,16] and suppression subtractive hybridization (SSH) approach in Marsupenaeus japonicus [17]; these genes were regarded as having a potential to be developed into sex markers. At DNA level, sex-linked AFLP marker was reported in the black tiger shrimp P. monodon [18].

Androgenic gland (AG) of crustacean is an endocrine gland unique to males. Since it was firstly identified in Orchestia gammarella by Charniaux-Cotton (1954), more and more evidence showed that AG played a key role in sex differentiation of crustacean [3, 19-24]. In penaeid shrimp, it was reported that destruction of AG at early juvenile stage could affect the development of the secondary sex characteristics of shrimp [25]. Research on sex determination and the achievement of female monosex culture in future shrimp aquaculture will require a method to determine the gender at early juvenile stages. Secondary sexual characteristics of juvenile shrimp are acquired through progressive molting, until development of external sex characteristics [26]. In this case, some markers which are closely related to the development of sex need to be developed in order to detect the sex ratio at early time. Due to the special function of AG in crustacean, it is possible to identify the specifically expressed genes in AG. The discovery of these genes is not only very helpful to understand the molecular mechanism of AG in sex determination of shrimp, but also to develop sex-specific markers at an early development stage.

SSH is regarded as a very powerful method to discover differentially expressed genes [27]. SSH was successfully used to identify a novel gene of unknown function in the epithelial cells of the male reproductive tract of Macrobrachium rosenbergii [28], Cq-IAG, and MrIAG which were uniquely expressed in the AG of Cherax quadricarinatus and Macrobrachium rosenbergii was also obtained by SSH [29, 30]. In the present study, SSH was used for screening the differentially expressed genes in male reproductive-related tissues, including AG and part of spermatophore, from Chinese shrimp F. chinensis. The expression of the genes with high abundance was detected in different tissues and different sex, and one potential transcriptomic sex marker of F. chinensis was isolated.

2. Materials and Methods

2.1. Shrimp and Tissues. Mature F. chinensis males, with a body length of 10.0 [+ or -] 0.5 cm and weight of 11.1 [+ or -] 0.5 g, were purchased from a local shrimp farm and reared in the aquarium of our institute. The target tissue located at the base of the fifth pereiopods (the approximate location of the AG in male F. chinensis, including AG and part of the spermatophore sac) and the control tissue, the basal of the fourth pereiopods were dissected from 20 male individuals and preserved in liquid nitrogen immediately for SSH library construction.

The tissues including hemocytes, muscle, gill, hepatopancreas, nerve cord, cuticle, eyestalk, ovary, testis, vas deferens, and the combined tissues of AG with part of spermatophore sac (AG was distributed scattered and hardly isolated in the Chinese shrimp) were sampled from five females or five males adult individuals and preserved in liquid nitrogen separately for verification of ESTs from the constructed MRT-SSH library.

The cephalothoraxes of five females or five males at grow-up stage (body length: 7.1 [+ or -] 0.3 cm and body weight: 5.1 [+ or -] 0.6 g) were sampled separately for primarily screening of sex markers.

Nineteen female juvenile Chinese shrimps (body length: 6.0 [+ or -] 0.5 cm and body weight: 3.0 [+ or -] 0.2 g) and 20 male juvenile Chinese shrimps (body length: 6.4 [+ or -] 0.5 cm and body weight: 3.7 [+ or -] 0.2 g) at stage PL75 (75 days after metamorphosis to postlarvae, when the external sex phenotype began to appear) were collected and their cephalothoraxes were dissected and preserved in liquid nitrogen individually for RNA extraction in order to be used for sex markers' screening.

Shrimps from different postlarvae (PL) stages, including PL15, PL30, PL45, PL60, PL75, PL90, and PL105, were also sampled for transcriptional detection of potent sex markers in different developmental stages.

2.2. Construction of the SSH Library. Total RNA was extracted from AG-containing target tissue (tester) and the control tissue (driver) using Unizol Reagent (BioStar, China) following the manufacturer's protocol. RNA quality was assessed by electrophoresis on 1.2% agarose gel. mRNA was then purified from total RNA with mRNA purification Kit (QIAGEN, Germany). Suppression subtractive hybridization (SSH) was performed with the PCR-Select cDNA Subtraction Kit (Clontech, USA). Briefly, tester double-strand cDNA and driver double-strand cDNA were synthesized from 2 each of the two mRNA samples and then digested with Rsa I. The digested tester cDNA was separated into two aliquots and then ligated to two different cDNA adaptors, respectively. During a first hybridization, excess driver was added to tester cDNA samples, which were then denatured and allowed to anneal. In the second hybridization, the two primary hybridization samples were mixed without denaturation. To further screen differentially expressed sequences, denatured driver cDNA was again added to these hybrid samples. As a result, the remaining subtracted equalized single-stranded tested cDNA reassociated to form hybrids with a different adaptor on each end. This subtracted sample was then used in PCR to amplify the differentially expressed sequences. The final PCR product was purified using the QIAGEN PCR Purification Kit, inserted into pGEM-T Easy vector (Promega, USA), then transformed into E. coli DH5a cells, plated onto LB medium containing ampicillin, X-gal, and IPTG, and then cultured overnight. White clones were selected randomly and amplified by PCR using Nested PCR primer 1 and 2R from PCR-Select cDNA Subtraction Kit. Agarose gel electrophoresis was performed to visualize the amplified fragments and to select the samples for sequencing from forward subtraction library (those from reverse subtraction library were not detected and sequenced). The previously mentioned PCR programs and control subtraction were all performed according to the manufacture's protocols.

2.3. Bioinformatic Analysis. The obtained cDNA sequences were first stripped of the vector and primer sequences using the online program BLAST. Clustering and assembly of the sequences were performed using ContigExpress (Informax 2003 software) with the following parameters: overlap: 20; identity: 0.85; cut-off score: 40. The resulting contigs and singlets were unified and their sequences were compared to the GenBank database using BLASTx analysis from NCBI. The sequences that had no hit in the GenBank database were carried out with Swiss-prot analysis.

2.4. Reverse Transcription-Polymerase Chain Reaction (RT PCR). Eleven contigs (contig10, 14, 16, 19, 26, 31, 32, 39, 47, 48, and CHH) from the MRT-SSH library were selected to be verified by RT-PCR. Total RNA, extracted from AG-containing target tissue, the control tissue, haemocytes, muscle, gill, hepatopancreas, nerve cord, cuticle, eyestalk, ovary, testis, vas deferens, and the combined tissues of AG with part of spermatophore sac, was treated with RQ1 RNase-Free DNase (Promega, USA) to remove contaminated DNA from the total RNA. cDNA was synthesized from 2 [micro]g total RNA by M-MLV reverse transcriptase (Promega, USA) following the manufacturer's protocol with random hexamer primer (5-NNN NNN-3'). The primer's sequences of 11 selected specific transcripts and 18S-rRNA were shown in Table 1. PCR reactions were performed with a denaturation step of 94[degrees]C for 4 min followed by 26 cycles of 94[degrees]C for 30 s, 50[degrees]C-64[degrees]C for 30 s, and 72[degrees]C for 30 s and then kept for 10 min at 72[degrees]C for the final extension. PCR products were analyzed on 2% agarose gel, stained with ethidium bromide, and visualized under ultraviolet light.

2.5. Screening of Sex Markers in Chinese Shrimp. Total RNA extraction and cDNA synthesis for the cephalothoraxes of female or male grow-up stage shrimp and each juvenile shrimp were performed as described previously.

Eleven selected genes were detected using RT-PCR in the cephalothoraxes of female and male shrimp for primarily screening of sex markers and detected in each juvenile for further screening of sex markers, respectively.

3. Results

3.1. Suppression Subtractive Hybridization. To testify the subtraction efficiency, control subtraction was carried out with human skeletal muscle tester (containing 0.2% HaeIII digested [phi]X174) and driver cDNAs, in parallel with the experimental forward and reverse subtraction according to the protocol of the kit. After the secondary PCR, correct [phi]X174/HaeIII bands appeared in both control subtraction (Figure 1, lane 5) and the positive PCR control (Figure 1, lane 7; which was provided by the kit, containing a successfully subtracted mixture of HaeIIIdigested [phi]X174 DNA). The experimental secondary PCR subtraction products (Figure 1, lanes 1 and 3) appeared as a smear from 0.2-2kb. After purification, the forward subtracted PCR products were used to generate forward subtracted libraries, with the titers of 3 x [10.sup.5] pfu/mL. The recombination rate was more than 97% with the majority of inserted cDNA fragments from 250 bp to 1000 bp.

3.2. Highly Expressed Genes in the AG-Related Tissues of Chinese Shrimp. In the MRT-SSH library, 432 clones were sequenced and 402 ESTs were obtained. They were further assembled into 152 nonredundant gene clusters, including 48 contigs and 104 singlets. As shown in Figure 1, the majority (82.6%) of the obtained ESTs shared no significant similarity (E > 1 x [10.sup.-4]) to any of the known genes and proteins in NCBI database; 2.0% of those ESTs shared significant similarity to the genes encoding hypothetical proteins without any annotation; the remaining sequences encoded 23 putative genes shown in Table 2.

Out of the 402 ESTs in the MRT-SSH library constructed in this study, genes related to neuropeptide hormone and hormone transporter account for 7.5% (30/402), which took a greater proportion than those related to ribo some protein 2.7% (11/402), RNA-binding protein (2.7%, 11/402), development and communication (1.0%, 4/402), immune (0.8%, 3/402), and enzyme (0.8%, 3/402) (Figure 2 The swissprot analysis result for the unknown sequences was shown in Supplementary Table 1 available online at

3.3. Validation of Selected Differentially Expressed Genes. Eleven transcripts with a high percentage in the MRTSSH library (Table 3)were selected for tissue distribution verification. As shown in Table 3, ESTs of contig10, 14,16, 19, 26, 31, 32, 39, 47, 48, and CHH accounted for 6.02%, 0.46%, 3.94%, 2.78%, 3.70%, 6.71%, 2.55%, 2.31%, 2.78%, 0.93%, and 5.09% in the total 402 ESTs, respectively. They were confirmed by RT-PCR in the AG-related tissues, control tissue, and other tissues. All the selected genes were only detected in the combined tissues of AG with part of the spermatophore sac except contig16, which was also detected in testis (Table 4).

3.4. A Potential Transcriptomic Sex Marker Was Selected by RT-PCR. As the selected 11 candidates were verified to be expressed either in AG-related tissues or in testis, both of which were located in the cephalothoraxes of shrimps, the cephalothoraxes of female and male grow-up stage shrimps were sampled to identify the genes expression in different sexes. All of them were only detected in male shrimps (Figure 3).

For further screening of sex markers in the Chinese shrimp, the selected genes were confirmed in 39 individuals at early juvenile stage (PL75), including 19 female shrimps and 20 male ones, by RT-PCR. Data showed that only contig16 (GenBank number KC354368) was confirmed to be expressed at the early juvenile stage PL75 in the shrimp and exclusively expressed in male ones (Figure 4).

To testify the availability of contig16 as a sex marker in the Chinese shrimp, the transcripts of contig16 were detected in different postlarvae stages, including PL15, PL30, PL45, PL60, PL75, PL90, and PL105. Data revealed that contig16 presented much earlier than PL75. Contig16 was firstly detected at a low expression level in the shrimp at PL45 (Figure 5).

4. Discussion

Suppression subtractive hybridization (SSH), which is regarded as an efficient method to isolate differentially expressed genes, is used to study the specifically expressed genes from AG-related tissues. In the sequenced 402 ESTs from the present SSH library, clones encoding neuropeptide hormone and hormone transporter accounted for the biggest part (7.46%, 30/402) in the total clone number. A fragment, with an annotation of hyperglycemic hormonelike neuropeptide 43-2 of Metapenaeus ensis (Table 2), aroused our interests. Crustacean hyperglycemic hormones (CHHs) are mainly detected in the X-organ sinus gland complex, which is situated in the eyestalks of crustacean 32] and considered to be playing important roles in multiple physiological effects, such as carbohydrate metabolism [33], reproduction [34], osmoregulation [35], and ecdysis [36]. Further study showed that the CHH gene homologue in the MRT-SSH library was exclusively detected at the epithelial cells in the internal wall of the spermatophore sac, which indicated that the CHH homologue might play roles in the male development of the shrimp F. chinensis [31].

Genes related to the ribosome proteins and RNA-binding proteins highly expressed in the SSH library constructed in this study. As we know, ribosome proteins are the proteins of the ribosomal subunits which are involved in the cellular process of translation. They were generally considered to function in the regulation and activity of the ribosome in cells [37, 38]. Ribosome proteins were also found to have functions in controlling cell growth and proliferation [39]. A recent study revealed that a ribosome protein L24 was significantly highly expressed in ovary than in other tissues and was considered to play an important role in oogenesis in the marine shrimp M. japonicus [38]. RNA-binding proteins play important roles in posttranscriptional control of RNAs, which is regarded as a vital way to regulate gene expression during development [40]. An RNA-binding protein, RBM25, was confirmed to play roles during programmed cell death via interaction with mRNAs of bcl-x [41]. Insulin-like androgenic gland hormone, IAG, plays a key role during male sex differentiation and spermatogenesis in crustacean [29, 30]. However, beyond our expectation, the IAG gene was not found in the MRT-SSH library. The reason might be that the IAG transcripts are expressed at a low level in the AG. In addition, the tester tissue used in the MRT-SSH library contained not only the AG, but also a big part of spermatophore, which might also lead to the absent of IAG in the limited sequencing ESTs.

In the constructed MRT-SSH library, as many as 82.89% of the obtained ESTs shared no significant similarity (E> 1 x [10.sup.-4])to any known genes and proteins in NCBI database, which took a significantly greater proportion when compared to the SSH library between testes of broodstock and juvenile shrimp of P. monodon (62.9% for forward library and 46.5% for reverse library) [42] and the SSH library between triploid and diploid shrimp of F. chinensis (39% for forward library and 35% for reverse library) [43]. Several cDNA libraries have also been constructed to isolate gonad-related genes in shrimps. In P. monodon, there were only 29.3% unidentified transcripts in the ovary cDNA library [15]. There was also a low proportion (32.4%) of unknown transcripts in the cDNA library of testes in P. monodon [16]. The high proportion of unknown genes in the MRT-SSH library indicated that there were plenty of new genes to be investigated in the AG and the spermatophore sac. More efforts should be made on the unknown genes in the MRT-SSH library as they occupied the greatest part of the assembled gene clusters of the library and some of them might play important roles in the male developmental activities. In order to learn more about the unknown genes expressed in MRT-SSH library, especially those genes with high expression frequency, 11 transcripts were selected to detect their expression patterns in different tissues or different sex individuals. Gonad-specific transcripts were already obtained from the SSH library in M. japonicus [17]. Above selected transcripts were all male-specific which inspired our interests to screen sex markers in the shrimp F. chinensis.

After a two-step screening of the selected gene clusters, the contig16, without annotation in the NCBI database, was finally verified to be specifically expressed in males at the juvenile stage PL75, when the external phenotypic sex characteristics of the shrimp began to be recognized. Histological studies revealed that the internal sex characteristics were detected much earlier than the external sex phenotype in penaeid shrimp [44, 45]. So the contig16 probably expressed at an earlier stage when the internal sex characteristics were developed. Detection of contig16 in developmental stages revealed that it could also be detected in PL45. This implied that contig16 had a potential to be developed as a transcriptomic sex marker in the shrimp F. chinensis to test the approximate gender ratio of the cultured shrimp at an early developmental stage.

The monosex culture of crustacean was tried and succeeded in Macrobrachium rosenbergii [3, 46]. However, no great progress was made in sex control of penaeid shrimp. The isolation of sex markers, which could be used to identify male shrimps from female ones during polyploidy breeding and aquaculture, would encourage us to speed up the establishment of monosex population culture.

In summary, an SSH library of the male reproductive-related tissues of the shrimp F. chinensis was successfully constructed. Most of the sequenced ESTs were assembled to be unknown genes and some of them were selected to verify the efficiency of the SSH library and to screen sex markers in the shrimp F. chinensis. A potential transcriptomic sex marker was isolated and could be used to detect the gender of Chinese shrimp at the early juvenile developmental stage. But more investigations should be taken to analyze the SSH library, especially on the biological function and characterization of the unknown genes. This is the basis to understand the molecular mechanism of male reproduction in order to develop sex control strategy in shrimp culture.


This work was financially supported by General Program of National Natural Science Foundation of China (30871909, 40676087, and 31072203) and Key Program of National Natural Science Foundation of China 30730071.


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[46] A. Sagi, Z. Ra'anan, D. Cohen, and Y. Wax, "Production of Macrobrachium rosenbergii in monosex populations: yield characteristics under intensive monoculture conditions in cages," Aquaculture, vol. 51, no. 3-4, pp. 265-275, 1986.

Shihao Li, (1) Fuhua Li, (1) Yusu Xie, (1), (2) Bing Wang, (1) Rong Wen, (1), (2) Chengsong Zhang, (1) Kuijie Yu, (1) and Jianhai Xiang (1)

(1) Key Laboratory of Experimental Marine Biology, Institute of Oceanology, Chinese Academy of Sciences, 7 Nanhai Road, Qingdao 266071, China

(2) Graduate University of Chinese Academy of Sciences, Beijing 100049, China

Correspondence should be addressed to Fuhua Li;

Received 10 May 2013; Revised 22 July 2013; Accepted 30 July 2013

Academic Editor: Katsutoshi Arai

TABLE 1: List of primers with their information used for RT-PCR.

Gene symbol   Gene common name   Primers 5'-3'

Contig10          Unknown        F-AAGTGGTGCTAGTCGTTGC

Contig14          Unknown        F-TGTGGACCTGCCTTCTT

Contig16          Unknown        F-GTGCTGGCGTCAGAGGGTAT

Contig19          Unknown        F-GTGAAACTGTGAGACTTATCCCTGT

Contig26          Unknown        F-AGAAGCGAGAATCATAAGAGG

Contig31          Unknown        F-CGTCCAGGTTTCATCGC

Contig32          Unknown        F-GAGGTTCTGATAAAGTCGTGGGT

Contig39          Unknown        F-ATGCTCCTCTTTGCTCTTCCGT

Contig47          Unknown        F-GAACCTGCTGAGGAACTTGAATGT

Contig48          Unknown        F-GAGGTTCTGATAAAGTCGTGG

CHH              Crustacean      F-GTTTTGTCCTCAAGCCTCTCTC
               hyperglycemic     R-GCGGAGTGGGACTACTTACC


Gene symbol   T ([degrees]C)   Product size (bp)

Contig10            54               336

Contig14            55               342

Contig16            60               539

Contig19            60               152

Contig26            53               213

Contig31            55               408

Contig32            60               119

Contig39            62               327

Contig47            62               158

Contig48            54               138

CHH                 57               289

18S-rRNA            64               257

F: forward; R: reverse; T:annealing temperature.

TABLE 2: Blast homology search results of genes isolated from the
MRT-SSH library.

Cluster          No. of   Highest BLASTX match         Accession
                 clones                                number

Neuropeptide       7      Ion-transport peptide          AAY29662
hormone and               precursor-like protein
hormone                   transcript 1
                   22#    Hyperglycemic hormone-like     AAD45234#
                          neuropeptide 43-2#

                   1      Sodium-neurotransmitter        EEC18529
                          symporter, putative

RNA binding        3      RD RNA-binding protein       XP_002714359
                   4      CRX like homeobox 2            ABC69291

                   1      Negative elongation factor     ABQ22564
                          E-like protein 25

                   1      RNA binding motif protein    XP_001916318

                   1      RBM25 protein                XP_001520202

Development        2      Putative senescence            BAB33414
- and                     -associated protein

                   1      Tetraspanins-like            ABM92445.1

                   1      Programmed cell death 4a      AAH54680

                   2      40S ribosomal protein S23     ABI52808

                   2      Ribosomal protein L26         ABP68820

                   2      Ribosomal protein L24         AAS45465

Ribosome           1      Putative ribosomal            ABM55572
protein                   protein L11

                   1      Ribosomal protein l13a        AAX62469

                   1      Ribosomal protein S4          AAV34860

                   1      Ribosomal protein L28        NP_001037237

                   1      Ribosomal protein S5          AAX62467
                          isoform A

Enzyme             1      Protease m1 zinc              EAT40060

                   1      Oligosaccharyl                EAT45977

Immune-related     2      Antimicrobial peptide         AAX63831
                   1      Antilipopolysaccharide        AAY33769

Cluster          No. of   Species              E value

Neuropeptide       7      Aedes aegypti        1B--05
and hormone
                   22     Metapenaeus ensis#   2E--09#

                   1      Ixodes scapularis    8E--61

RNA binding        3      Oryctolagus          8E--06
protein                   cuniculus

                   4      Homo sapiens         7E--08

                   1      Callithrix jacchus   2E--06

                   1      Equus caballus       3E--04

                   1      Ornithorhynchus      5E--07

Development- and   2      Pisum sativum        3E--28
-related protein   1      Fenneropenaeus       1E--99

                   1      Danio rerio          7E--17

Ribosome protein   2      Argas monolakensis   1E--50

                   2      Penaeus monodon      6E--22

                   2      Marsupenaeus         7E--11

                   1      Maconellicoccus      1E--33

                   1      Lysiphlebus          5E--23

                   1      Bombyx mori          8E--55

                   1      Bombyx mori          2E--24

                   1      Lysiphlebus          1E--79

Enzyme             1      Aedes aegypti        9E--36

                   1      Aedes aegypti        2E--23

Immune-related     2      Fenneropenaeusx      2E--22
protein                   protein

                   1      Litopenaeus          3B--21

The specific expression patterns for the identified genes in bold
letters was confirmed in another Study (Li et al., 2010 [31]).

Note: The specific expression patterns for the identified genes
indicated with #.

TABLE 3: Clones percentage of the selected contigs or gene clusters
in the SSH library.

Gene symbol   Clones number   Clones percentage (%)

contig10          26                   6.02
contig14           2                   0.46
contig16          17                   3.94
contig19          12                   2.78
contig26          16                   3.7
contig31          29                   6.71
contig32          11                   2.55
contig39          10                   2.31
contig47          12                   2.78
contig48           4                   0.93
CHH               22                   5.09

TABLE 4: Tissue distribution of selected genes from AG-SSH library
of F. chinensis.

Gene symbol   Hc   Mc   Gi   Hp   Nc   Cu   Es   Ov   Te   AG&Sm   C

contig10      -    -    -    -    -    -    -    -    -      +     -
contig14      -    -    -    -    -    -    -    -    -      +     -
contig16      -    -    -    -    -    -    -    -    +      +     -
contig19      -    -    -    -    -    -    -    -    -      +     -
contig26      -    -    -    -    -    -    -    -    -      +     -
contig31      -    -    -    -    -    -    -    -    -      +     -
contig32      -    -    -    -    -    -    -    -    -      +     -
contig39      -    -    -    -    -    -    -    -    -      +     -
contig47      -    -    -    -    -    -    -    -    -      +     -
contig48      -    -    -    -    -    -    -    -    -      +     -
CHH           -    -    -    -    -    -    -    -    -      +     -

-: not detected; +: detected; Hc: hemocytes; Mc: muscle; Gi: gill; Hp:
hepatopancreas; Nc: nervecord; Cu: cuticle; Es: eyestalk; Ov: ovary;
Te: testis; AG & Sm: androgenic gland with part of spermatophore sac;
C: control tissue.

FIGURE 2: Percentages (%) of ESTs related to gene function in the
MRT-SSH library. (1) Unknown genes; (2) neuropeptide hormone/hormone
transporter; (3) ribosome protein; (4) RNA binding protein;
(5) hypothetical protein; (6) related to development/communication;
(7) immune related; (8) enzyme.

1   82.6%
2    7.5%
3    2.7%
4    2.7%
5    2.0%
6    1.0%
7    0.8%
8    0.8%

Note: Table made from bar graph.
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Title Annotation:Research Article
Author:Li, Shihao; Li, Fuhua; Xie, Yusu; Wang, Bing; Wen, Rong; Zhang, Chengsong; Yu, Kuijie; Xiang, Jianha
Publication:Journal of Marine Biology
Article Type:Report
Date:Jan 1, 2013
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