Molecular characterization and mRNA transcript profile of vitellogenin in Chinese shrimp, Fenneropenaeus chinensis

Retinoid X receptor modulates vitellogenin gene expression in black tiger shrimp, Penaeus monodon

Effective inducing of ovarian maturation in female shrimp broodstock is important for successful breeding programs. Vitellogenesis is a biochemical process during which a yolk protein precursor vitellogenin (Vg) is synthesized and thus, can be used to indicate ovarian maturation stage. In this study, transcriptional regulation of Vg synthesis in the black tiger shrimp, Penaeus monodon was investigated. Genome walking on 5' upstream sequence of Vg gene revealed several putative binding sites of lipophilic retinoic acid response elements (RARE), and nuclear hormone responsive elements. Deletion of RARE significantly reduced the promoter activity to drive the expression of luciferase reporter gene in Sf-9 cells. To validate the trans-factor that potentially controls Vg expression through RARE, a cDNA encoding retinoid X receptor (PmRXR), one of the RARE-bound transcription factors was cloned from P. monodon's ovary. PmRXR expression was detected in various shrimp tissues, and was up-regulated during ovary development in a similar way to Vg expression. The DNA-binding domain of PmRXR protein showed specific binding to RARE-containing region on Vg 5' upstream sequence as determined by Electrophoretic Mobility Shift Assay (EMSA). Furthermore, dsRNA-mediated PmRXR silencing in previtellogenic and vitellogenic shrimp revealed that suppression of PmRXR could reduce Vg transcript in both stages. Taken together, the results presented in this study indicate that RXR is possibly an activator protein that modulates Vg expression in shrimp ovary through the binding to RARE.

Abundances of vitellogenin and heat shock protein 90 during ovarian and embryonic development of Exopalaemon carinicauda

To evaluate functions of vitellogenin (Vg) and heat shock protein 90 (Hsp90) during ovarian and embryonic development of Exopalaemon carinicauda, the cDNA of Vg (Ec-Vg) was cloned, and the abundances of Ec-Vg and heat shock protein 90 (Hsp90) (Ec-Hsp90) were determined during ovarian and embryonic development. During ovarian development, the concentration of Vg protein in hemolymph was markedly greater than in the ovary and hepatopancreas, and was greatest at sexual maturity. The relative abundance of Ec-Vg mRNA transcript was greatest in the hepatopancreas and almost undetectable in hemocytes. By combining mRNA transcript relative abundances with morphological results, a model was developed to explain the mRNA transcript relative abundance of Ec-Hsp90 and Ec-Vg during ovarian and embryonic development. The relative abundance of Ec-Vg mRNA transcript was greatest during the recovery period after reproduction had occurred (Stage V) and mature stage (Stage IV) in the ovary or hepatopancreas, respectively. There were marked associations of the patterns of Ec-Hsp90 and Ec-Vg mRNA transcript abundances both in hepatopancreas and ovary. During embryonic development, the relative abundance of the two mRNA transcripts were greatest at the metazoea and protozoea stages, respectively. These results indicate that Ec-Vg is produced primarily in the hepatopancreas, secreted into the hemolymph and transported into growing oocytes. It, therefore, is believed that Ec-Vg has an important function in the overall ovarian development and late embryonic development of E. carinicauda. In contrast, Ec-Hsp90 is a regulatory factor for Vg transcription and is important during early organogenesis in E. carinicauda.

Two distinct vitellogenin genes are similar in function and expression in the bigfin reef squid Sepioteuthis lessoniana

Unlike vitellogenin, which is the sole major precursor of yolk protein in all oviparous vertebrates, a variety of major precursor of yolk proteins are found among oviparous invertebrates. Sea urchins have a transferrin-like yolk protein, while all other major precursors of yolk proteins in oviparous invertebrates belong to the superfamily of large lipid transfer proteins (LLTPs). However, a comprehensive understanding of vitellogenesis is absent in cephalopods. To understand control of vitellogenesis by the LLTPs gene, two vitellogenins (VTG1 and VTG2), two apolipophorins (APOLP2A and APOLP2B), and a cytosolic large subunit of microsomal triglyceride transfer protein (MTTP) found in the bigfin reef squid. Only the two VTGs showed high levels of expression in mature females compared to males. We further analyzed the expression profile and localization of both VTGs/VTGs during ovarian development. Our data showed that VTGs/VTGs expressions were correlated to the female reproductive cycle. Ovarian VTG1 and VTG2 were localized in the follicle cells but not in oocytes. In addition, VTG1 and VTG2 were represented in follicle cells and oocytes. Thus, our results showed that both VTGs were synthesized by follicle cells and are then delivered to oocytes. In addition, we demonstrated that VTGs were the major precursor of yolk protein in bigfin reef squid. We also found differential proteolytic cleavage processes of VTG1 and VTG2 during VTGs accumulation in oocytes. Therefore, our data shed light on the molecular mechanism of the yolk accumulation pathway in cephalopods.

Transcriptomic information from Pacific white shrimp (Litopenaeus vannamei) ovary and eyestalk, and expression patterns for genes putatively involved in the reproductive process

The increased use of massive sequencing technologies has enabled the identification of several genes known to be involved in different mechanisms associated with reproduction that so far have only been studied in vertebrates and other model invertebrate species. In order to further investigate the genes involved in Litopenaeus vannamei reproduction, cDNA and SSH libraries derived from female eyestalk and gonad were produced, allowing the identification of expressed sequences tags (ESTs) that potentially have a role in the regulation of gonadal maturation. In the present study, different transcripts involved in reproduction were identified and a number of them were characterized as full-length. These transcripts were evaluated in males and females in order to establish their tissue expression profiles during developmental stages (juvenile, subadult and adult), and in the case of females, their possible association with gonad maturation was assessed through expression analysis of vitellogenin. The results indicated that the expression of vitellogenin receptor (vtgr) and minichromosome maintenance (mcm) family members in the female gonad suggest an important role during previtellogenesis. Additionally, the expression profiles of genes such as famet, igfbp and gpcr in brain tissues suggest an interaction between the insulin/insulin-like growth factor signaling pathway (IIS) and methyl farnesoate (MF) biosynthesis for control of reproduction. Furthermore, the specific expression pattern of farnesoic acid O-methyltransferase suggests that final synthesis of MF is carried out in different target tissues, where it is regulated by esterase enzymes under a tissue-specific hormonal control. Finally, the presence of a vertebrate type steroid receptor in hepatopancreas and intestine besides being highly expressed in female gonads, suggest a role of that receptor during sexual maturation.

Molecular characterization and expression of vitellogenin gene from Spodoptera exigua exposed to cadmium stress

In this study, we cloned a full-length cDNA encoding vitellogenin (Vg) in Spodoptera exigua. The complete Vg cDNA consists of 5694 nucleotides with a long open reading frame encoding 1761 amino acid residues. The deduced amino acid sequence shared high similarity with the Vgs of other lepidopteran insects, particularly in the C-terminal region including the GL/ICG motif, five cysteine residues and DGXR motif. We analyzed the spatiotemporal expression of Vg transcripts in S. exigua by RT-PCR and Real-time Quantitative PCR. The results revealed that Vg was expressed specifically in the female fat body and was detectable after 5th day female pupae. The maximum level of Vg mRNA appeared in 48-h-old female adults and started to decrease quickly. When exposed to cadmium (Cd) (25-100mg/kg), there was a significantly decreased Vg level in female adults. The information presented in this study suggested the Vg in S. exigua could be significantly affected by Cd pressure.

A comparative study of vitellogenesis in Echinodermata: Lessons from the sea star

The provision of yolk precursor proteins to the oviparous egg is crucial for normal embryo development. In Echinodermata, a transferrin-like yolk component termed major yolk protein (MYP) is a major precursor protein in Echinoidea and Holothuroidea. In contrast, in Asteroidea a single vitellogenin (Vtg) was recently identified, but its role as primary yolk protein remains unclear. To resolve the apparent MYP-Vtg dichotomy in sea stars and to understand the dynamics of candidate yolk protein gene expression during the reproductive cycle, we investigated the molecular structures of sea star Vtg and MYP and quantified their transcript levels during oogenesis. By combining protein sequencing of the predominant proteins in ovulated eggs of Patiriella regularis with ovarian transcriptome sequencing and molecular cloning, we characterized two cDNAs encoding two bona fide Vtgs (PrVtg1 and PrVtg2) and a partial cDNA encoding MYP (PrMYP). PrMYP mRNA was found in low abundance in growing oocytes, possibly as maternal transcripts for translation after ovulation. In contrast, PrVtg transcripts, whose levels varied during the reproductive cycle, were not found in developing oocytes - rather, they were detected in ovarian follicle cells and pyloric caeca, indicating an extra-oocytic origin. Vtg accumulating in oocytes was stored in the form of cleaved products, which constituted the most abundant yolk polypeptides in ovulated sea star eggs; their levels decreased during early embryonic and larval development. Together, these traits are the hallmarks of a classical yolk protein - and hence, we contend that Vtg, and not MYP, is the main yolk protein in asteroids.

Gonadal transcriptomic analysis and differentially expressed genes in the testis and ovary of the Pacific white shrimp (Litopenaeus vannamei)

Background

The Pacific white shrimp (Litopenaeus vannamei) is the world’s most prevalent cultured crustacean species. However, the supply of high-quality broodstocks is limited and baseline information related to its reproductive activity and molecular issues related to gonad development are scarce. In this study, we performed transcriptome sequencing on the gonads of adult male and female L. vannamei to identify sex-related genes.

Results

A total of 25.16 gigabases (Gb) of sequences were generated from four L. vannamei gonadal tissue libraries. After quality control, 24.11 Gb of clean reads were selected from the gonadal libraries. De-novo assembly of all the clean reads generated a total of 65,218 unigenes with a mean size of 1021 bp and a N50 of 2000 bp. A search of all-unigene against Nr, SwissProt, KEGG, COG and NT databases resulted in 26,482, 23,062, 20,659, 11,935 and 14,626 annotations, respectively, providing a total of 30,304 annotated unigenes. Among annotated unigenes, 12,320 unigenes were assigned to gene ontology categories and 20,659 unigenes were mapped to 258 KEGG pathways. By comparing the ovary and testis libraries, 19,279 testicular up-regulated and 3,529 ovarian up-regulated unigenes were identified. Enrichment analysis of differentially expressed unigenes resulted in 1060 significantly enriched GO terms and 34 significantly enriched KEGG pathways. Nine ovary-specific, 6 testis-specific, 45 testicular up-regulated and 39 ovarian up-regulated unigenes were then confirmed by semi-quantitative PCR and quantitative real-time PCR. In addition, using all-unigenes as a reference, a total of 13,233 simple sequence repeats (SSRs) were identified in 10,411 unigene sequences.

Conclusions

The present study depicts the first large-scale RNA sequencing of shrimp gonads. We have identified many important sex-related functional genes, GO terms and pathways, all of which will facilitate future research into the reproductive biology of shrimp. We expect that the SSRs detected in this study can then be used as genetic markers for germplasm evaluation of breeding and imported populations.

Electronic supplementary material

The online version of this article (doi:10.1186/s12864-015-2219-4) contains supplementary material, which is available to authorized users.

Transcriptome analysis of red swamp crawfish Procambarus clarkii reveals genes involved in gonadal development

Background

The red swamp crawfish, Procambarus clarkii, has become one of the most economically important cultured species in China. Currently, little is known about the gonadal development of this species. Isolation and characterization of genes are an initial step towards understanding gonadal development of P. clarkii.

Results

Using the 454 pyrosequencing technology, we obtained a total of 1,134,993 high quality sequence reads from the crawfish testis and ovary libraries. We aimed to identify different genes with a potential role in gonad development. The assembly formed into 22,652 isotigs, distributed by GO analysis across 55 categories in the three ontologies, ‘molecular function’, ‘cellular component’, and ‘biological processes’. Comparative transcript analysis showed that 1,720 isotigs in the ovary were up-regulated and 2138 isotigs were down-regulated. Several gonad development related genes, such as vitellogenin, cyclin B, cyclin-dependent kinases 2, Dmc1 and ubiquitin were identified. Quantitative real-time PCR verified the expression profiles of 14 differentially expressed genes, and confirmed the reliability of the 454 pyrosequencing.

Conclusions

Our findings provide an archive for future research on gonadal development at a molecular level in P. clarkii and other crustacean. This data will be helpful to develop new ideas for artificial regulation of the reproductive process in crawfish aquaculture.

Vitellogenin is not an appropriate biomarker of feminisation in a crustacean

The expression of the yolk protein vitellogenin (Vtg) has been used as a biomarker of feminisation in multiple fish species throughout the world. Since the late 1990s, researchers have attempted to develop similar biomarkers to address whether reproductive endocrine disruption also occurs in the males of invertebrate groups such as the Crustacea. To date, the vast majority of studies investigating Vtg induction in male Crustacea have resulted in negative or inconclusive results, leading researchers to question the utility of Vtg expression as a biomarker in this taxon. This study measured the expression of Vtg genes in two intersex phenotypes (termed internal and external) found in the male amphipod, Echinogammarus marinus, and compared them with those of normal males and females. Males presenting the external intersex phenotype are infected with known feminising parasites and display a variety of feminised traits including oviduct structures on their testes and external female brood plates (oostegites). The internal intersex male phenotype, that displays a pronounced oviduct structure on the testes without the external intersex characteristics, is not parasite infected and it is thought to be a result of environmental contamination. Given their morphology, these phenotypes might be considered highly 'feminised' or 'de-masculinised' and can be utilised to test the suitability of feminisation biomarkers. The E. marinus transcriptome was searched for genes resembling Vtg and two sequences were revealed, that we subsequently refer to as Vtg1 and Vtg2. Results from a high-throughput transcriptomic sequencing screen of gonadal cDNA libraries suggested that very low expression (in this manuscript gene transcription is taken to represent gene expression, although it is acknowledged that in addition to transcription, translation, transcript processing, mRNA stability and protein stability can regulate gene expression) of Vtg1 and Vtg2 in normal males (ESTs=1 and 0 for Vtg1 and Vtg2, respectively), internal intersex males (ESTs=0 for both Vtg sequences) and external intersex males (ESTs=5 and 0 for Vtg1 and Vtg2, respectively). In contrast, the sequencing suggested notable levels of expression of both Vtg genes in females (ESTs=1133 and 84 for Vtg1 and Vtg2, respectively). Subsequent qPCR analysis validates these expression levels, with the signal for Vtg1 and Vtg2 transcripts in all male phenotypes being indistinguishable from that caused by contamination of trace levels of genomic DNA or the low-level amplification non-target sequences. These findings suggest that Vtg expression is not notably induced in highly feminised amphipods and is therefore not an appropriate biomarker of feminisation/de-masculination in crustaceans. We discuss our findings in the context of previous attempts to measure Vtg in male crustaceans and suggest a requirement for more appropriate taxon-specific biomarkers to monitor feminisation in these groups.

Vitellogenin of Fujian oyster, Crassostrea angulata: Synthesized in the ovary and controlled by estradiol-17β

In this study, we cloned a full-length cDNA encoding vitellogenin (Vg) in the Fujian oyster Crassostrea angulata. The complete Vg cDNA consists of 5160 nucleotides with a long open reading frame encoding 1641 amino acid residues. The deduced amino acid sequence shared high similarity with the Vgs of other mollusc, fish, nematode and arthropod species, particularly in the N-terminal region. We analyzed the spatiotemporal expression of caVg transcripts by Real-time Quantitative PCR. In common with other mollusc Vgs, the caVg gene was expressed primarily in the ovary, and the levels were 348 and 177 times higher in maturation and ripeness stages (P<0.01), respectively, than in the partially spent stage. There was negligible expression in male oysters. In situ hybridization analysis further localized caVg mRNA to the follicle cells (also named auxiliary cells) surrounding the oocytes in the ovary. Moreover, in vivo waterborne exposure experiments in early gametogenesis oysters showed that estradiol-17β (E2) administration resulted in a significant increase in caVg mRNA expression. We conclude that caVg is synthesized in the follicle cell surrounding the vitellogenic oocyte in C. angulata, and directly passed to oocytes through the extracellular space without mediation through hemolymph. Also, we hypothesize that this process is mediated by E2 in a dose dependent.

MnHSP90 cDNA characterization and its expression during the ovary development in oriental river prawn, Macrobrachium nipponense

Heat shock protein 90 (HSP90) is not only involved in environmental stress but also plays roles in the ovary development in some vertebrates. To understand its role in crustacean, we examined the HSP90 cDNA for the first time in the ovary and hepatopancreas of the oriental river prawn, Macrobrachium nipponense and designated this protein as MnHSP90 in this study. The MnHSP90 was cloned by the methods of degenerated oligonucleotide primers and rapid amplification of the cDNA ends (RACE). Bioinformatics analysis showed that the MnHSP90 cDNA was 2,684 bp in length, containing a 126 bp 5' untranslated region (UTR), a 359 bp 3' UTR, and an open reading frame (ORF) of 2,199 bp encoding a 732-amino acid polypeptide with predicted molecular mass of 84.3 KDa. Sequence alignment showed that the MnHSP90 shared 72-79% identity with other animals. Real-time quantitative PCR (qPCR) analysis demonstrated that the MnHSP90 mRNA was ubiquitously detected in all tested tissues, with the highest expression in the thoracic ganglia, the mediate in heart, muscle and intestine, and the lowest in haemocytes and gills. The MnHSP90 mRNA levels in the hepatopancreas and ovary of M. nipponense reached a maximum at the stage III (early vitellogenic stage) and stage IV (later vitellogenic stage) ovaries, respectively, and then decreased significantly in both tissues as the ovarian development proceeded. The level of MnHSP90 expression in the hepatopancreas was higher than that in the ovary when compared with in the same ovarian developmental stage. Our results indicate that MnHSP90 is involved in ovarian development in oriental river prawn and may play a regulatory role in ovary maturation.

N-glycan moieties of the crustacean egg yolk protein and their glycosylation sites

Vitellogenin (Vg) is the precursor of the egg yolk glycoprotein of crustaceans. In the prawn Macrobrachium rosenbergii, Vg is synthesized in the hepatopancreas, secreted to the hemolymph, and taken up by means of receptor-mediated endocytosis into the oocytes. The importance of glycosylation of Vg lies in its putative role in the folding, processing and transport of this protein to the egg yolk and in the fact that the N-glycan moieties could provide a source of carbohydrate during embryogenesis. The present study describes, for the first time, the structure of the glycan moieties and their sites of attachment to the Vg of M. rosenbergii. Bioinformatics analysis revealed seven putative N-glycosylation sites in M. rosenbergii Vg; two of these glycosylation sites are conserved throughout the Vgs of decapod crustaceans from the Pleocyemata suborder (N 159 and N 660). The glycosylation of six putative sites of M. rosenbergii Vg (N 151, N 159, N ,168 N ,614 N 660 and N 2300) was confirmed; three of the confirmed glycosylation sites are localized around the N-terminally conserved N-glycosylation site N 159. From a theoretical three-dimensional structure, these three N-glycosylated sites N 151, N 159, and N 168 were localized on the surface of the Vg consensus sequence. In addition, an uncommon high mannose N-linked oligosaccharide structure with a glucose cap (Glc1Man9GlcNAc2) was characterized in the secreted Vg. These findings thus make a significant contribution to the structural elucidating of the crustacean Vg glycan moieties, which may shed light on their role in protein folding and transport and in recognition between Vg and its target organ, the oocyte.

Molecular characterization and expression of vitellogenin (Vg) genes from the cyclopoid copepod, Paracyclopina nana exposed to heavy metals

Induction of vitellogenin (Vg) has been used as a biomarker of exposure to heavy metals and endocrine-disruption chemicals (EDCs) in aquatic organisms. Here, we identified the full-length Vg1 and Vg2 sequence from the brackish water copepod, Paracyclopina nana. Vg1 gene contained 5718bp of the open reading frame (ORF) that encoded the putative protein of 1905 amino acids residues, while Vg2 gene consisted of 5442bp of ORF, encoding the putative protein of 1813 amino acids residues. P. nana Vgs showed highly conserved domains in the N-terminal region. The phylogenetic analysis revealed that P. nana Vgs are distinct from other arthropods, such as insects and decapods, as it formed a clade with other copepods, Tigriopus japonicus and salmon louse (Lepeophtheirus salmonis). The expression of Vg transcripts was detectable after the copepodid stages 4-5. Female copepods expressed over 83 times and 223 times more Vg1 and Vg2 transcripts, respectively, than males. When copepods were exposed to heavy metals (0.1mg/L Cd, 0.4mg/L Cu, and 2mg/L AsIII) for 24, 48, 72, and 96h, P. nana Vg transcripts were highly induced in a time-dependent manner. Interestingly, Vg2 gene was more susceptible than Vg1 to trace heavy metal exposure. This finding indicates that P. nana Vgs provide a potential indicator for assessing the toxic effect of heavy metals. In addition, we suggest P. nana as a potential model species for risk-assessment to environmental pollutants in brackish water.