Characterization of two vitellogenin cDNAs from a Pandalus shrimp (Pandalopsis japonica): expression in hepatopancreas is down-regulated by endosulfan exposure

Genome-Wide Identification of Vitellogenin Gene Family and Comparative Analysis of Their Involvement in Ovarian Maturation in Exopalaemon carinicauda

Vitellogenin (Vtg) is a precursor of yolk proteins in egg-laying vertebrates and invertebrates and plays an important role in vitellogenesis and embryonic development. However, the Vtg family remains poorly characterized in Exopalaemon carinicauda, a major commercial mariculture species found along the coasts of the Yellow and Bohai Seas. In this study, 10 Vtg genes from the genomes of E. carinicauda were identified and characterized. Phylogenetic analyses showed that the Vtg genes in crustaceans could be classified into four groups: Astacidea, Brachyra, Penaeidae, and Palaemonidae. EcVtg genes were unevenly distributed on the chromosomes of E. carinicauda, and a molecular evolutionary analysis showed that the EcVtg genes were primarily constrained by purifying selection during evolution. All putative EcVtg proteins were characterized by the presence of three conserved functional domains: a lipoprotein N-terminal domain (LPD_N), a domain of unknown function (DUF1943), and a von Willebrand factor type D domain (vWD). All EcVtg genes exhibited higher expression in the female hepatopancreas than in other tissues, and EcVtg gene expression during ovarian development suggested that the hepatopancreas is the main synthesis site in E. carinicauda. EcVtg1a, EcVtg2, and EcVtg3 play major roles in exogenous vitellogenesis, and EcVtg3 also plays a major role in endogenous vitellogenesis. Bilateral ablation of the eyestalk significantly upregulates EcVtg mRNA expression in the female hepatopancreas, indicating that the X-organ/sinus gland complex plays an important role in ovarian development, mostly by inducing Vtg synthesis. These results could improve our understanding of the function of multiple Vtg genes in crustaceans and aid future studies on the function of EcVtg genes during ovarian development in E. carinicauda.

Persistent organic pollutants (POPs) in marine crustaceans: Bioaccumulation, physiological and cellular responses

Persistent organic pollutants (POPs) are ubiquitous in marine ecosystems. These compounds can be accumulated in water, sediments and organisms, persist in time, and have toxic effects in human and wildlife. POPs can be uptaken and bioaccumulated by crustaceans, affecting different physiological processes, including energy metabolism, immunity, osmoregulation, excretion, growth, and reproduction. Nonetheless, animals have evolved sub-cellular mechanisms for detoxification and protection from chemical stress. POPs induce the activity of enzymes involved in xenobiotic metabolism and antioxidant systems, that in vertebrates are importantly regulated at gene expression (transcriptional) level. However, the activation and control of these enzyme systems upon the exposure to POPs have been scarcely studied in invertebrate species, including crustaceans. Herein, we summarize various aspects of the bioaccumulation of POPs in marine crustaceans and their physiological effects. We specially focus on the regulation of xenobiotics metabolism and antioxidant enzymes as key sub-cellular mechanisms for detoxification and protection from chemical stress.

The DUF1943 and VWD domains endow Vitellogenin from Crassostrea gigas with the agglutination and inhibition ability to microorganism

Vitellogenin (Vg) is the major precursor of the egg-yolk proteins, which mainly acts as an energy reserve molecule for providing nutrients during embryonic development. Vg also plays an immune function in vertebrates such as fish, but there are few studies on the immune function of Vg in invertebrates. In the present study, a Vg homologue (CgVg) was identified and characterized in oyster Crassostrea gigas. There are three domains in the CgVg protein, including a Vitellogenin_N domain, a domain of unknown function 1943 (DUF1943) and a von Willebrand factor type D domain (VWD). The mRNA transcripts of CgVg were detected in all tested tissues with high expression in the gonad, hepatopancreas and haemocytes, which was 466.29-, 117.15- and 57.49-fold (p < 0.01) of that in adductor muscle, respectively. After Vibrio splendidus stimulation, the mRNA expression level of CgVg in haemocytes increased significantly at 6, 12 and 24 h, which was 1.97-, 3.58- and 1.3-fold (p < 0.01) of that in the seawater group, respectively. The immunofluorescence assay showed that positive signals of CgVg protein were mainly located at the cytoplasm of haemocytes. The recombinant protein of DUF1943 domain (rDUF1943) and VWD domain (rVWD) was able to bind lipopolysaccharide (LPS), mannose (MAN), peptidoglycan (PGN) and poly (I:C), as well as Gram-positive bacteria (Staphylococcus aureus and Micrococcus luteus), Gram-negative bacteria (Escherichia coli and V. splendidus) and fungi (Pichia pastoris). rDUF1943 exhibited stronger agglutination activity towards S. aureus, M. luteus, E. coli, V. splendidus and P. pastoris, while agglutination was only observed in the rVWD group towards P. pastoris. The rVWD inhibited the growth of E. coli, S. aureus and V. splendidus, while no antibacterial activity was detected in rDUF1943 group. Collectively, CgVg not only functioned as a pattern recognition receptor (PRR) to bind various microorganisms and PAMPs, but also as an immune effector participating in the clearance of invaders, in which DUF1943 and VWD domain were mainly responsible for agglutinating and inhibiting microorganism respectively.

Large lipid transfer proteins in hepatopancreas of the mud crab Scylla paramamosain

Large lipid transfer proteins (LLTPs) are extensively involved in various physiological processes. In the present study, five LLTP sequences encoding apolipocrustacein 1 (apoCr 1), apoCr 2, precursor of the large discoidal lipoprotein (dLp) and high density lipoprotein/β-glucan binding protein (HDL-BGBP) (dLp-BGBP), microsomal triglyceride transfer protein (MTP) and clotting protein (CP) were identified in the hepatopancreas of Scylla paramamosain. Of these, apoCr 2, dLp-BGBP, and MTP were newly identified in this species, and the former two proteins were classified into the APO family while the later into the MTP family in phylogenetic trees. The apoCr 1 expression level was dramatically increased in the hepatopancreas towards ovarian maturation, which was extremely greater than that in the ovaries concurrently, likely to meet the considerable requirements of yolk protein and lipids for embryo development. The dLp-BGBP expression level in male crabs was comparable to that in female crabs, supporting HDL-BGBP acts as a major circulatory lipid carrier. The close phylogenetic relationship between dLp-BGBP and the scaffolding protein of lipid transfer particle implied dLp might facilitate lipid transfer between the hepatopancreas and HDL-BGBP-containing lipoproteins. The MTP expression level was positively related to ovarian development in both the hepatopancreas and ovaries, indicating MTP may be involved in lipoprotein assembly in the hepatopancreas and lipid droplet maturation in the ovaries. CP may play a crucial role in embryo development based on high expression level observed in the testes of mature crabs. Our findings provide novel insights into LLTP superfamily members and their functions in decapods.

Does estrogen regulate vitellogenin synthesis in corals?

Most broadcast spawner corals have a vitellogenic phase that lasts at least 6 months. It is established that estrogen regulates vitellogenin synthesis in vertebrates. Although some research have been conducted on the physiological role of sex steroids in corals, little is known about their involvement in oocyte development. This study aimed to detect steroid hormones - progesterone, testosterone, and estradiol-17β (E2) - in Acropora tenuis and study the relationships between vitellogenesis/vitellogenin synthesis and these steroids. This study also investigated the effect of E2 on vitellogenin synthesis in corals and identified steroidogenic enzymes in A. tenuis genome. Branches from tagged coral colonies were collected monthly from March to November. Histological observations showed that oocytes were vitellogenic from March to May (Stage IV and V), but not in June, and that gonads were occupied by immature oocytes in September (Stage I). Real-time qPCR revealed that vitellogenin (vg1 and vg2) transcript levels in coral branches were high in April and May, implying that corals actively underwent vitellogenesis during these months, and spawned before June. Liquid chromatography-mass spectrometry revealed that E2 could be detected in coral branches in March, April, and May, but not in June, whereas testosterone and progesterone did not fluctuate much in the same months. Immersing branches in E2-containing seawater failed to increase vitellogenin transcript levels. The results indicate that E2 is involved in oogenesis but does not positively regulate vitellogenin synthesis. Steroidogenic enzymes (except CYP19A) were identified in A. tenuis, suggesting that corals may endogenously synthesize progestogens and androgens from cholesterol.

Suppression of a Novel Vitellogenesis-Inhibiting Hormone Significantly Increases Ovarian Vitellogenesis in the Black Tiger Shrimp, Penaeus monodon

In this study, a novel Crustacean Hyperglycemic Hormone-type II gene (CHH-type II) was identified and biologically characterized in a shrimp, Penaeus monodon. Based on its structure and function, this gene was named P. monodon vitellogenesis-inhibiting hormone (PemVIH). The complete cDNA sequence of PemVIH consisted of 1,022 nt with an open reading frame (ORF) of 339 nt encoding a polypeptide of 112 amino acids. It was classified as a member of the CHH-type II family based on conserved cysteine residues, a characteristically positioned glycine residue, and the absence of CHH precursor-related peptide (CPRP) domain. The deduced mature PemVIH shared the highest sequence similarities with giant river prawn sinus gland peptide A. Unlike P. monodon gonad-inhibiting hormone (PemGIH), PemVIH was expressed only in the brain and ventral nerve cord, but not the eyestalks. Whole mount immunofluorescence using a newly generated PemVIH antiserum detected positive signals in neuronal cluster 9/11 and 17 of the brain, commissural ganglion (CoG), and neuronal clusters of ventral nerve cord. The presence of PemVIH-positive neurons in CoG, a part of stomatogastric nervous system, suggested a potential mechanism for crosstalk between nutritional and reproductive signaling. The role of PemVIH in vitellogenesis was evaluated using RNA interference technique. Temporal knockdown of PemVIH in female subadults resulted in a 3-fold increase in ovarian vitellogenin expression, suggesting an inhibitory role of PemVIH in vitellogenesis. This study provided novel insight into the control of vitellogenesis and additional strategies for improving ovarian maturation in P. monodon without the current harmful practice of eyestalk ablation.

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.

Molecular approaches underlying the oogenic cycle of the scleractinian coral, Acropora tenuis

This study aimed to elucidate the physiological processes of oogenesis in Acropora tenuis. Genes/proteins related to oogenesis were investigated: Vasa, a germ cell marker, vitellogenin (VG), a major yolk protein precursor, and its receptor (LDLR). Coral branches were collected monthly from coral reefs around Sesoko Island (Okinawa, Japan) for histological observation by in situ hybridisation (ISH) of the Vasa (AtVasa) and Low Density Lipoprotein Receptor (AtLDLR) genes and immunohistochemistry (IHC) of AtVasa and AtVG. AtVasa immunoreactivity was detected in germline cells and ooplasm, whereas AtVG immunoreactivity was detected in ooplasm and putative ovarian tissues. AtVasa was localised in germline cells located in the retractor muscles of the mesentery, whereas AtLDLR was localised in the putative ovarian and mesentery tissues. AtLDLR was detected in coral tissues during the vitellogenic phase, whereas AtVG immunoreactivity was found in primary oocytes. Germline cells expressing AtVasa are present throughout the year. In conclusion, Vasa has physiological and molecular roles throughout the oogenic cycle, as it determines gonadal germline cells and ensures normal oocyte development, whereas the roles of VG and LDLR are limited to the vitellogenic stages because they act in coordination with lipoprotein transport, vitellogenin synthesis, and yolk incorporation into oocytes.

Crustacean Hemolymph Lipoproteins

Lipoproteins mediate the transport of apolar lipids in the hydrophilic environment of physiological fluids such as the vertebrate blood and the arthropod hemolymph. In this overview, we will focus on the hemolymph lipoproteins in Crustacea that have received most attention during the last years: the high density lipoprotein/β-glucan binding proteins (HDL-BGBPs), the vitellogenins (VGs), the clotting proteins (CPs) and the more recently discovered large discoidal lipoproteins (dLPs). VGs are female specific lipoproteins which supply both proteins and lipids as storage material for the oocyte for later use by the developing embryo. Unusual within the invertebrates, the crustacean yolk proteins-formerly designated VGs-are more related to the ApoB type lipoproteins of vertebrates and are now termed apolipocrustaceins. The CPs on the other hand, which are present in both sexes, are related to the (sex specific) VGs of insects and vertebrates. CPs serve in hemostasis and wound closure but also as storage proteins in the oocyte. The HDL-BGBPs are the main lipid transporters, but are also involved in immune defense. Most crustacean lipoproteins belong to the family of the large lipid transfer proteins (LLTPs) such as the intracellular microsomal triglyceride transfer protein, the VGs, CPs and the dLPs. In contrast, the HDL-BGBPs do not belong to the LLTPs and their relationship with other lipoproteins is unknown. However, they originate from a common precursor with the dLPs, whose functions are as yet unknown. The majority of lipoprotein studies have focused on decapod crustaceans, especially shrimps, due to their economic importance. However, we will present evidence that the HDL-BGBPs are restricted to the decapod crustaceans which raises the question as to the main lipid transporting proteins of the other crustacean groups. The diversity of crustaceans lipoproteins thus appears to be more complex than reflected by the present state of knowledge.

Environmental Pollutants Impair Transcriptional Regulation of the Vitellogenin Gene in the Burrowing Mud Crab (Macrophthalmus Japonicus)

Vitellogenesis is a pivotal reproductive process of the yolk formation in crustaceans. Vitellogenin (VTG) is the precursor of main yolk proteins and synthesized by endogenous estrogens. The intertidal mud crab (Macrophthalmus japonicus) inhabits sediment and is a good indicator for assessing polluted benthic environments. The purpose of this study was to identify potential responses of M. japonicus VTG under environmental stresses caused by chemical pollutants, such as 1, 10, and 30 µg L−1 concentrations in di(2-ethylhexyl) phthalate (DEHP), bisphenol A (BPA) and irgarol. We characterized the M. japonicus VTG gene and analyzed the transcriptional expression of VTG mRNA in M. japonicus exposed to various chemicals and exposure periods. A phylogenetic analysis revealed that the M. japonicus VTG clustered closely with Eriocheir sinensis (Chinese mitten crab) VTG, in contrast with another clade that included the VTG ortholog of other crabs. The basal level of VTG expression was the highest in the hepatopancreas and ovaries, and tissues. VTG expression significantly increased in the ovaries and hepatopancreas after 24 h exposure to DEHP. Increased responses of VTG transcripts were found in M. japonicus exposed to DEHP and BPA for 96 h; however, VTG expression decreased in both tissues after irgarol exposure. After an exposure of 7 d, VTG expression significantly increased in the ovaries and hepatopancreas for all concentrations of all chemicals. These results suggest that the crustacean embryogenesis and endocrine processes are impaired by the environmental chemical pollutants DEHP, BPA, and irgarol.

Development of homologous enzyme-linked immunosorbent assays to quantify two forms of vitellogenin in guppy (Poecilia reticulata)

Guppy (Poecilia reticulata) is a promising model organism in toxicological studies, and vitellogenin (Vtg) is a commonly used biomarker for environmental estrogens. Although an ELISA for guppy Vtg has been developed previously, we found that guppy had two forms of Vtgs. In this study, two Vtgs were characterized and enzyme-linked immunosorbent assays (ELISAs) for each Vtg were developed. Two Vtgs purified from 17β-estradiol (E₂)-exposed guppy were characterized as phospholipoglycoproteins with molecular weights of ~ 520 and ~ 480 kDa, respectively. In SDS-PAGE, one purified Vtg appeared as three major bands of ~ 210, ~ 126, and ~ 102 kDa, and the other revealed a clear band of ~ 68 kDa. Matrix-assisted laser desorption/ionization-time of flight/time of flight mass spectrometry analysis showed that they were VtgAb and VtgC. Using purified Vtgs and their corresponding antibodies, two sandwich ELISAs with working ranges of 7.8~1000 and 15.6~500 ng/mL were developed. Precision tests showed that intra- and inter-assay coefficients of variations of both ELISAs were below 10%. Parallelism between Vtg standard curves and serial dilutions of whole body homogenate from E₂-exposed guppy confirmed that two ELISAs could quantify guppy Vtgs. Furthermore, two ELISAs were used to measure Vtg inductions in liver, caudal fin and whole body of male guppy exposed to 17a-ethinylestradiol to validate their use for detecting estrogenic effects of exogenous chemicals. These homologous Vtg ELISAs will promote the use of guppy as a model organism to study estrogenic chemicals.

Functional characterization of Vitellogenin_N domain, domain of unknown function 1943, and von Willebrand factor type D domain in vitellogenin of the non-bilaterian coral Euphyllia ancora: Implications for emergence of immune activity of vitellogenin in basal metazoan

Our understanding of the function of vitellogenin (Vg) in reproduction has undergone a transformation over the past decade in parallel with new insights into the role of Vg in immunity. However, the time when Vg was endowed with immunological activities during animal evolution remains elusive. Here we demonstrate for the first time that the recombinant proteins rVitellogenin_N, rDUF1943, and rVWD from Vg of the basal metazoan coral Euphyllia ancora not only interact with Gram-positive and negative bacteria as well as their conserved surface components LTA and LPS but also enhance phagocytosis of bacteria by macrophages. Moreover, challenge with LPS results in a marked up-regulation of vg in the coral E. ancora. These data suggest that E. ancora Vg, like that described in the bilaterian oviparous animals fish and amphioxus, is a molecule related to antibacterial defense, indicating that the timing of the emergence of immune role of Vg predates the divergence of the cnidarian (non-bilaterian) and bilaterian lineages.

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.

Molecular cloning, expression, purification and characterization of vitellogenin in scallop Patinopecten yessoensis with special emphasis on its antibacterial activity

Vitellogenin (Vg), the major precursor of the egg-yolk proteins, has been found to play an immune role in fish and protochordate amphioxus, however, no study on the immune function of Vg in invertebrates has ever been studied before. In this study, the complete cDNA of Vg was identified from the scallop Patinopecten yessoensis (termed PyVg). The cDNA contained an open reading frame (ORF) of 6888 bp, encoding a polypeptide of 2295 amino acid protein, which had an N-terminal signal peptide followed by the mature Vg. The mature Vg had the domains Vitellogenin_N, domain of unknown function 1943 (DUF1943) and von Willebrand factor type D domain (VWD) as well as the consensus cleavage site (R-X-R/K-R) and conserved motif (KTIGNAG). Tissue distribution assay revealed that PyVg transcripts were predominantly present in the ovary and hepatopancreas, and its expression profile in ovary well reflected the annual cycle of vitellogenesis. Interestingly, bacterial challenge caused a significant change in PyVg expression, hinting an involvement of PyVg in the acute phase response in P. yessoensis. Consistently, recombinant DUF1943 and VWD domains both could interact with LTA and LPS on bacterial wall, and purified native PyVg displayed a broad-spectrum antibacterial activity against both Gram-negative (Escherichia coli and Vibrio anguillarum) and Gram-positive bacteria (Staphylococcus aureus). Overall, these data indicate that Vg is a pattern recognition molecule with bacterial growth-inhibiting activity in the scallop.

Molecular characterization and developmental expression of vitellogenin in the oriental river prawn Macrobrachium nipponense and the effects of RNA interference and eyestalk ablation on ovarian maturation

Vitellogenin (Vg) is the precursor of yolk protein, which functions as a nutritive resource that is important for embryonic growth and gonad development. In this study, the cDNA encoding the Vg gene from the oriental river prawn Macrobrachium nipponense was cloned using expressed sequence tag (EST) analysis and the rapid amplification of cDNA ends (RACE) approach. The transcript encoded 2536 amino acids with an estimated molecular mass of 286.810 kDa. Quantitative real-time PCR indicated high expression of Mn-Vg in the female ovary, hemocytes, and hepatopancreas. As ovaries developed, the expression level of Mn-Vg increased in both the hepatopancreas and ovary. In the hepatopancreas, the expression level rose more slowly at the early stage of vitellogenesis and reached the peak more rapidly compared to the expression pattern in ovary. The observed changes in Mn-Vg expression level at different development stages suggest the role of nutrient source in embryonic and larval development. Eyestalk ablation caused the Mn-Vg expression level to increase significantly compared to eyestalk-intact groups during the ovary development stages. Ablation accelerated ovary maturation by removing hormone inhibition of Mn-Vg in the hepatopancreas and ovary. In adult females, Mn-Vg dsRNA injection resulted in decreased expression of Mn-Vg in both the hepatopancreas and ovary, and two injection treatment dramatically delayed ovary maturation. Vg RNA interference down-regulated the vitellogenin receptor (VgR) expression level in the ovary, which illustrates the close relationship between Vg and VgR in the process of vitellogenesis.

Transcriptome analysis of the differences in gene expression between testis and ovary in green mud crab (Scylla paramamosain)

Background

The green mud crab (Scylla paramamosain) is the most prevalent crustacean on the southeast coast of China. The molecular regulatory mechanism of sex determination and gonadal differentiation in this species has received considerable attention in recent years because of the huge differences—both biological and economic—between male and female crabs. In this study, next-generation sequencing technology was used to develop deep-coverage transcriptomic sequencing data for the testis and ovary of S. paramamosain.

Results

A total of 365,116 reads (testis 171,962, ovary 193,154) with an average sequence length of 285 bp were produced from testis and ovary cDNA libraries. After filtering out contaminating reads, the clean reads were assembled, producing a total of 21,791 isotigs and leaving 22,814 reads as singlets. Using the BLASTX program, 3,471 unique sequences (2,275 isotigs and 1,196 singletons) were annotated with known protein sequences from the NCBI non-redundant (Nr) protein sequence database. The Gene Ontology and KEGG (Kyoto Encyclopedia of Genes and Genomes) analyses allowed the 224 unique sequences that were annotated with enzyme code (EC) numbers to be mapped into 174 KEGG pathways. After comparing the ovary and testis libraries, 4,021 gonad-differentially, 10,522 ovary-specifically, and 19,013 testis-specifically expressed genes were identified. Moreover, 33 ovary-specific, 14 testis-specific, and 34 gonad-differential transcripts were confirmed by semi-quantitative PCR and quantitative real-time PCR. In addition, 8,610 putative simple sequence repeats (SSRs) and 23,879 potential single nucleotide polymorphisms (SNPs) were identified.

Conclusion

This is the first large-scale RNA sequencing of S. paramamosain to be reported. We have identified many important functional genes and made a preliminary attempt to construct the regulatory network involved in the gonadal development of crustaceans. The annotated transcriptome data will provide fundamental support for future research into the reproduction biology of S. paramamosain. A large number of candidate SSRs and SNPs were detected, which could be used as genetic markers for population genetics and functional genomics in this species.

Electronic supplementary material

The online version of this article (doi:10.1186/1471-2164-15-585) contains supplementary material, which is available to authorized users.

Four cDNAs encoding lipoprotein receptors from shrimp (Pandalopsis japonica): structural characterization and expression analysis during maturation

As in all other oviparous animals, lipoprotein receptors play a critical role in lipid metabolism and reproduction in decapod crustaceans. Four full-length cDNAs encoding lipoprotein receptors (Paj-VgR, Paj-LpR1, Paj-LpR2A, and Paj-LpR2B) were identified from Pandalopsis japonica through a combination of EST screening and PCR-based cloning. Paj-LpR1 appears to be the first crustacean ortholog of insect lipophorin receptors, and its two paralogs, Paj-LpR2A and Paj-LpR2B, exhibited similar structural characteristics. Several transcriptional isoforms were also identified for all three Paj-LpRs. Each expression pattern was unique, suggesting different physiological roles for these proteins. Paj-VgR is an ortholog of vitellogenin (Vg) receptors from other decapod crustaceans. A phylogenetic analysis of lipoproteins and their receptors suggested that the nomenclature of Vgs from decapod crustaceans may need to be changed. A PCR-based transcriptional analysis showed that Paj-VgR and Paj-LpR2B are expressed almost exclusively in the ovary, whereas Paj-LpR1 and Paj-LpR2A are expressed in multiple tissues. The various transcriptional isoforms of the three Paj-LpRs exhibited unique tissue distribution profiles. A transcriptional analysis of each receptor using tissues with different GSI values showed that the change in transcription of Paj-VgRs, Paj-LpR2A and Paj-LpR1 was not as significant as that of Vgs during maturation. However, the transcriptional levels of Paj-LpR2B decreased in ovary at maturation, suggesting that their transcriptional regulation is involved in reproduction.

Differences in gene organization between type I and type II crustins in the morotoge shrimp, Pandalopsis japonica

Crustins are cysteine-rich cationic antimicrobial peptides (AMPs) found in decapod crustaceans. Six novel crustin genes (Paj-CrusIc, Id, Ie, If, IIb and IIc) were identified in the morotoge shrimp, Pandalopsis japonica. Deduced amino acid sequences of isolated Paj-Crus genes ranged from 99 to 178 amino acid residues (10.6-17.8 kDa). Sequence analysis of nine isolated Paj-Crus genes and 100 different crustins from various decapod crustaceans revealed that a splice site and KXXXCP motif within the WAP domain may be the main criteria for classifying type I and II crustins, suggesting that the two types of crustin genes may have been generated by different processes. We also identified three intron-less crustin I genes (Paj-Crus Id, Ie and If) for the first time, which may have been generated by gene duplication. The tissue distribution profiles showed that Paj-CrusI genes were expressed predominantly in the gill and epidermis, whereas Paj-CrusII genes were expressed ubiquitously, suggesting that the two types of crustins may play different roles in various tissues or under different physiological conditions. Differing from previous results, hemocyte-specific crustin was not isolated from Pandalopsis japonica. This study showed that both types of crustin genes (types I and II) exist in decapod crustaceans and their primary structure and expression profiles differ from each other, suggesting that they may play different biological roles. This will help to extend our knowledge of the crustacean innate immune response, which will provide important basic information of shrimp immunity against various pathogens.

Molecular characterization of three crustin genes in the morotoge shrimp, Pandalopsis japonica

Crustins are among the most important antimicrobial peptides (AMPs) found in decapod crustaceans. They are small cationic AMPs (5-7 kDa) characterized by a proline-rich amino-terminal domain and a cysteine-rich carboxyl-terminal domain. Here, the first 3 crustin-like cDNAs (Pj-crus Ia, Ib, and II) were identified from the morotoge shrimp, Pandalopsis japonica. The full-length cDNAs of Pj-crus Ia, Ib, and II consisted of 1135, 580, and 700 nucleotides and encoded putative proteins containing 109, 119, and 186 amino acids residues, respectively. All 3 identified Pj-crus sequences exhibited the conserved domain organization for crustins, including a signal sequence, a cysteine-containing region, a glycine-rich region, and a whey-acidic protein (WAP) domain. Amino acid sequence comparisons and phylogenetic analysis revealed that the Pj-crus Ia and Ib belong to type I crustins (e.g., carcinin), which have been mostly identified from Brachyura and Astacidea, whereas Pj-crus II was classified as belonging to the type II crustins, which are mainly found in Dendrobranchiata. An analysis of the organization of these 3 Pj-crus genes revealed that the splicing site within the WAP domain may be an important key for classifying types I and II crustin family members. The tissue distribution profile results showed that the Pj-crus I genes were expressed in a tissue-specific manner but that the Pj-crus II gene was expressed ubiquitously, suggesting that these crustins may play different roles in various tissues or under different physiological conditions. The bacterial challenge results suggested that the Pj-crus genes may be transcriptionally influenced by different bacterial types. This comparative study of various crustin family members will help extend the knowledge on the crustacean innate immune response, which will provide important basic information for controlling shrimp immunity against various pathogens.

Two type I crustacean hyperglycemic hormone (CHH) genes in Morotoge shrimp (Pandalopsis japonica): cloning and expression of eyestalk and pericardial organ isoforms produced by alternative splicing and a novel type I CHH with predicted structure shared with type II CHH peptides

Crustacean hyperglycemic hormone (CHH) peptide family members play critical roles in growth and reproduction in decapods. Three cDNAs encoding CHH family members (Pj-CHH1ES, Pj-CHH1PO, and Pj-CHH2) were isolated by a combination of bioinformatic analysis and conventional cloning strategies. Pj-CHH1ES and Pj-CHH1PO were products of the same gene that were generated by alternative mRNA splicing, whereas Pj-CHH2 was the product of a second gene. The Pj-CHH1 and Pj-CHH2 genes had four exons and three introns, suggesting the two genes arose from gene duplication. The three cDNAs were classified in the type I CHH subfamily, as the deduced amino acid sequences had a CHH precursor-related peptide sequence positioned between the N-terminal signal sequence and C-terminal mature peptide sequence. The Pj-CHH1ES isoform was expressed at a higher level in the eyestalk X-organ/sinus gland (XO/SG) complex and at a lower level in the gill. The Pj-CHH1PO isoform was expressed at higher levels in the XO/SG complex, brain, abdominal ganglion, and thoracic ganglion and at a lower level in the epidermis. Pj-CHH2 was expressed at a higher level in the thoracic ganglion and at a lower level in the gill. Real-time polymerase chain reaction was used to quantify the effects of eyestalk ablation on the mRNA levels of the three Pj-CHHs in the brain, thoracic ganglion, and gill. Eyestalk ablation reduced expression of Pj-CHH1ES in the brain and Pj-CHH1PO and Pj-CHH2 in the thoracic ganglion. Sequence alignment of the Pj-CHHs with CHHs from other species indicated that Pj-CHH2 had an additional alanine at position #9 of the mature peptide. Molecular modeling showed that the Pj-CHH2 mature peptide had a short alpha helix (α1) in the N-terminal region, which is characteristic of type II CHHs. This suggests that Pj-CHH2 differs in function from other type I CHHs.