Hepatopancreas and ovary are sites of vitellogenin synthesis as determined from partial cDNA encoding of vitellogenin in the marine shrimp,Penaeus vannamei

Ovarian development pattern and vitellogenesis of ridgetail white prawn, Exopalaemon carinicauda

The ridgetail white prawn Exopalaemon carinicauda has the potential to be used as a model organism in crustacean research because it has a transparent body, available draft genome, and short life cycle. However, their ovarian development pattern remains unclear under laboratory culture conditions. This study investigated the changes of ovarian external feature, ovarian histology, gonadosomatic index (GSI), and hepatosomatic index (HSI), as well as the expression and localization of vitellogenin in the ovary and the hepatopancreas during the first ovarian development cycle of E. carinicauda under laboratory-reared condition. The results demonstrated that (1) the first ovarian development cycle of E. carinicauda could be divided into 5 different stages in which the ovary changes its color from white to yellow during the vitellogenesis process in parallel with increasing GSI. (2) After pubertal molt, most females reached ovarian stage II while the females reached stage V after premating molt. (3) During the ovarian development, GSI increased smoothly and HSI relatively stable during the period of stages I to IV, while GSI increased but HSI decreased significantly from stages IV to V. (4) In situ hybridization (ISH) revealed that EcVg was slightly expressed in the oocyte cytoplasm of previtellogenic oocytes. The positive signal was mainly detected in hepatopancreatic fibrillar cells, and a strong signal was found in the hepatopancreas at stage IV. Moreover, the expression level of EcVg-mRNA in the hepatopancreas is stage-specific, and the hepatopancreas contributes majority of vitellin precursor protein to support the ovarian development of E. carinicauda.

Vitellogenin Receptor (VgR) Mediates Oocyte Maturation and Ovarian Development in the Pacific White Shrimp (Litopenaeus vannamei)

Oocyte maturation and ovarian development are sequentially coordinated events critical to reproduction. In the ovaries of adult oviparous animals such as birds, bony fish, insects, and crustaceans, vitellogenin receptor (VgR) is a plasma membrane receptor that specifically mediates vitellogenin (Vg) transport into oocytes. Accumulation of Vg drives sexual maturation of the female crustaceans by acting as a pivotal regulator of nutritional accumulation within oocytes, a process known as vitellogenesis. However, the mechanisms by which VgR mediates vitellogenesis are still not fully understood. In this study, we first identified a unique VgR (Lv-VgR) and characterized its genomic organization and protein structural domains in Litopenaeus vannamei, a predominant cultured shrimp species worldwide. This newly identified Lv-VgR phylogenetically forms a group with VgRs from other crustacean species within the arthropod cluster. Duplicated LBD/EGFD regions are found exclusively among arthropod VgRs but not in paralogs from vertebrates and nematodes. In terms of expression patterns, Lv-VgR transcripts are specifically expressed in ovaries of female shrimps, which increases progressively during ovarian development, and rapidly declines toward embryonic development. The cellular and subcellular locations were For analyzed by in situ hybridization and immunofluorescence, respectively. The Lv-VgR mRNA was found to be expressed in the oocytes of ovaries, and Lv-VgR protein was found to localize in the cell membrane of maturing oocytes while accumulation of the ligand Vg protein assumed an even cytoplasmic distribution. Silencing of VgR transcript expression by RNAi was effective for stunting ovarian development. This present study has thus provided new insights into the regulatory roles of VgR in crustacean ovarian development.

JNK signaling pathway regulates the development of ovaries and synthesis of vitellogenin (Vg) in the swimming crab Portunus trituberculatus

The development of Portunus trituberculatus egg cells is directly related to the nutritional status of the fertilized egg, which affects the key production stages of offspring hatching. Vitellogenin plays a key role in the nutrient supply required for the development of the egg cells. The c-Jun N-terminal kinase (JNK) is an important member of the mitogen-activated protein kinase (MAPK) superfamily and plays an important role in cell proliferation, transformation, differentiation, and apoptosis. At present, there are no reports on the involvement of the JNK signaling pathway in the reproductive regulation of P. trituberculatus. In this study, rapid amplification of complementary DNA ends amplification technology was used to clone the full length of JNK complementary DNA, which has a length of 2094 bp, including an open reading frame (ORF) of 1266 bp encoding a 421-amino acid protein. The protein includes the S_TKC conserved domain with a TPY phosphorylation site, which is a typical feature of the JNK gene family. Observing tissue sections found the oocytes in the inhibitor group developed slowly, while the oocytes in the activated group showed accelerated development. Meanwhile, Portunus trituberculatus JNK and vitellogenin (Vg) genes exhibited the same trend in the hepatopancreas and ovaries, and the expression of the SP600125 group was downregulated (P < 0.05), while the anisomycin group was upregulated (P < 0.05). In addition, JNK enzyme activity and vitellin (Vn) content in the ovarian tissue showed that the JNK activity of the SP600125 group decreased, while activity increased in the anisomycin group. The accumulation of Vn content in the SP600125 group decreased, and that in the anisomycin group increased. In summary, after injection with inhibitor or activator, the JNK signaling pathway of P. trituberculatus was inhibited or activated, the accumulation of Vn in the ovary was reduced or increased, and ovarian development was inhibited or accelerated, respectively. These results indicated that the JNK signaling pathway is involved in the regulation of Vg synthesis and ovarian development in P. trituberculatus. The results of this study further add to the knowledge of the breeding biology of P. trituberculatus and provide a theoretical reference for the optimization of breeding techniques in aquaculture production systems.

Vitellogenesis in spiders: first analysis of protein changes in different reproductive stages of Polybetes pythagoricus

Vitellogenesis represents one of the most vital processes of oviparous species during which various proteins, carbohydrates, and lipids are synthesized and stored inside the developing oocytes. Through analyzing protein changes in the midgut diverticula, hemolymph, and ovaries of females throughout the different vitellogenic stages of the spider Polybetes pythagoricus, we determined the origin of the different proteins involved in the formation of lipovitellins (LVs) along with the existence of a linkage between the hemocyanin and this vital process. An increase in the total protein content of the midgut diverticula, hemolymph, and ovary occurred throughout vitellogenesis followed by a decrease in those levels after laying. The presence of hemocyanin in egg and in LV2, as well as its accumulation in the ovary throughout the vitellogenesis process, was determined. Considering that all biologic processes depend on the correct structure and function of proteins, this study establishes, for the first time for the Order Araneae, the coexistence of three different origins of vitellogenesis-related proteins: one predominantly ovarian involving peptides of 120, 75, 46, and 30 kDa; another extraovarian one originated from the midgut diverticula and represented by a 170 kDa peptide, and a third hemolymphatic one, represented by the 67 kDa peptide.

Ecdysone receptor in the mud crab Scylla paramamosain: a possible role in promoting ovarian development

In arthropods, it is known that ecdysteroids regulate molting, limb regeneration, and reproduction through activation of the ecdysone receptor (EcR). However, the ecdysteroid signaling pathway for promotion of ovarian development in crustaceans is still unclear. In this study, three cDNA isoforms of EcR were cloned from the mud crab Scylla paramamosain. qRT-PCR revealed that the SpEcR mRNA was abundant in the eyestalk, ovary and epidermis. During ovarian development, the SpEcR transcripts increased from stage I (undeveloped stage) and reached a peak at stage IV (late vitellogenic stage) before dropping to a lower level at stage V (mature stage). Meanwhile, levels of 20-hydroxyecdysone (20E) in the hemolymph, detected by HPLC-MS, displayed a similar pattern of increase with ovarian development. Results from in situ hybridization indicated that SpEcR mRNA was present in the follicular cells during vitellogenesis. Results from in vivo experiments revealed that 20E at 0.2 μg/g body weight significantly stimulated the expression of SpEcR and vitellogenin (SpVg) in female crabs during the early vitellogenic stage but not during the previtellogenic stage. This was confirmed by results from in vitro experiments which indicated that SpEcR and SpVg expression levels were significantly upregulated in early vitellogenic ovarian explants incubated with 5.0 μM 20E at 3 and 6 h but not in previtellogenic ovarian explants. Finally, results from in vitro gene silencing experiments indicated that the expression of SpEcR and SpVg in the ovary was significantly inhibited by SpEcR dsRNA. All these results together indicated that in S. paramamosain, 20E, and SpEcR, located in the follicular cells, play important roles in the promotion of ovarian development via regulating the expression of SpVg.

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.

Potential roles of transglutaminase and thioredoxin in the release of gonad-stimulating factor in Penaeus monodon: implication from differential expression in the brain during ovarian maturation cycle

The synthesis of vitellogenin during ovarian maturation in crustacean is induced by gonad-stimulating factor(s) that are synthesized in the brain and thoracic ganglia. This process is negatively regulated by a gonad-inhibiting hormone (GIH) from the eyestalk. This study utilized differential-display RT-PCR technique to identify putative genes in brain and thoracic ganglia that may be involved in ovarian maturation of the black tiger shrimp, Penaeus monodon under the condition in which the expression of GIH was suppressed by GIH-specific dsRNA. After excluding redundant clones and subsequent verification by RT-PCR, 10 and 5 transcripts exhibited up-regulated and down-regulated expressions, respectively, in the GIH-dsRNA injected shrimp when compared with the Tris/NaCl injected shrimp. Among the up-regulated genes, a full sequence of thioredoxin cDNA was cloned, and nucleotide sequence analysis showed that it was highly similar to other crustacean thioredoxin. The thioredoxin gene as well as the other four genes including transglutaminase and three unknowns; U10-11, U10-15 and U13-11 that were up-regulated upon GIH-knockdown exhibited similar expression profile in the brain during ovarian maturation cycle. The highest expression level was detected in the brain of early-vitellogenic female shrimp suggesting that they are required for an initial stage of vitellogenesis. Our results posted for the first time a possible function of transglutaminase and thioredoxin in regulating the gonad-stimulating pathway in the brain of the shrimp.

Cloning and expression of ecdysone receptor (EcR) from the intertidal copepod, Tigriopus japonicus

Ecdysteroids are steroid hormones that play an important role in development, growth, molting of larva, and reproduction in the Arthropoda. The effect of ecdysteroids is mediated by its binding to ecdysteroid receptor (EcR). To investigate the role of EcR during development and the effect to environmental stressors on EcR expression in a copepod, we isolated and characterized cDNA and 5'-promoter region of the Tigriopus japonicus EcR (TJ-EcR), and studied mRNA expression pattern. The full-length TJ-EcR cDNA sequence was 1962bp in length and the open reading frame encoded 546 amino acids. The deduced TJ-EcR protein contained well-conserved DNA-binding domain and ligand-binding domain. Phylogenetic analysis revealed that TJ-EcR was clustered with the EcR of other crustaceans. TJ-EcR mRNA was expressed in a developmental stage-specific manner: high in early developmental stages and low in the adult stage. Significantly elevated expression of the TJ-EcR gene in adults was detected at hypersalinity (42ppt) and high temperature (35 degrees C) condition. The 5'-flanking region of TJ-EcR gene contains heat shock protein 70 response elements, implying that the environmental stressors may affect its expression via the stress-sensor. In addition, bisphenol A (100microg/L) repressed TJ-EcR expression. Our results suggest that TJ-EcR could be a biomarker for the monitoring of the impact of environmental stressors in copepods.

Gene discovery from an ovary cDNA library of oriental river prawn Macrobrachium nipponense by ESTs annotation

The oriental river prawn, Macrobrachium nipponense, is an important crustacean species in aquaculture. However, early gonad maturity is a ubiquitous problem which devalues the product quality. While husbandry and nutritional management have achieved little success in tackling this issue, a molecular approach may discover the genes involved in reproduction and development, which will provide the basic knowledge on reproductive control. In this study, a high-quality cDNA library of prawn was constructed from the ovary tissue. A total of 3294 successful sequencing reactions yielded 3256 expressed sequence tags (ESTs) longer than 100 bp. The cluster and assembly analyses yielded 1514 unique sequences including 414 contigs and 1168 singletons. About 719 (47.49%) unique sequences were identified as orthologs of genes from other organisms. By sequence comparability analysis, 28 important genes including cathepsin B, chromobox protein, Cdc2, cyclin B, DEAD box protein and ADF/cofilin protein were expressed. These genes may be involved in reproductive and developmental functions in prawn. Peritrophin consisting of cortical rods was also found in this species. The identification of these EST sequences in M. nipponense would improve our understanding on the genes that regulate reproduction and development in prawn species. This study also lays the groundwork for development of molecular markers related to ovary development in other prawn species.

Crustacean endocrine toxicology: a review

Crustaceans are major constituents to aquatic ecosystems that provide a variety of ecological and economic services. Individual crustacean species are adept at occupying diverse niches and their success, in part, stems from neuro-endocrine signaling cascades that regulate physiology in response to environmental and internal cues. Peptide hormones are major signal transducers in crustaceans. The crustacean hyperglycemic hormone family of peptides regulates various aspects of growth, reproduction, and metabolism. These peptides may function as the terminal hormone to regulate some physiological activities or may function as intermediates in a signaling cascade. Ecdysteroids and terpenoids are two major classes of terminal signaling molecules in these cascades. Hormones from these two classes function independently or in concert to regulate various processes. Ecdysteroid signaling is subject to toxicological disruption through disturbances in ecdysteroid synthesis or binding of toxicants to the ecdysteroid receptor. Methyl farnesoate is the major terpenoid hormone of crustaceans and also is susceptible to disruption by environmental chemicals. However, the methyl farnesoate signaling pathway is poorly understood and only limited mechanistic confirmation for disruption of this endocrine signaling pathway exists. Disruption of the ecdysteroid/terpenoid signaling pathways in crustaceans has been associated with aberrations in growth, metamorphosis, reproductive maturation, sex determination, and sex differentiation. Population studies have revealed disruptions in crustacean growth, molting, sexual development, and recruitment that are indicative of environmental endocrine disruption. However, environmental factors other that pollution (i.e., temperature, parasitism) also can elicit these effects and definitive causal relationships between endocrine disruption in field populations of crustaceans and chemical pollution is generally lacking.

Reproduction obstacles for the female green neon shrimp (Neocaridina denticulata) after exposure to chlordane and lindane

The purpose of this study was to investigate the effects of chlordane and lindane on reproduction obstacles and endocrine disruption in female green neon shrimp (Neocaridina denticulata). Individuals of N. denticulata, a common inhabitant of freshwater systems in Taiwan, was exposed to different levels of chlordane (1 and 10 ngl(-1)) and lindane (0.1 and 1 microgl(-1)). The reproductive ability and reproductive hormone levels were observed after exposure. According to our findings, an increase in estrogen, induction of a vitellogenin-like protein, and changes in reproductive performance were observed in both chlordane- and lindane-treated shrimp. Thus, it was concluded that chlordane and lindane may cause some reproduction obstacles and disruption of endocrine functions in N. denticulata.

Complete sequence of Litopenaeus vannamei (Crustacea: Decapoda) vitellogenin cDNA and its expression in endocrinologically induced sub-adult females

The gene that encodes vitellogenin (Vg), the precursor of the major yolk protein, vitellin, is expressed during vitellogenesis in decapod crustaceans. In this study, we sequenced the full-length cDNA from the Pacific white shrimp Litopenaeus vannamei Vg gene (LvVg). This is the first open thelycum penaeid shrimp Vg cDNA to be sequenced. The transcript encodes a 2587 amino acid polypeptide with up to 85% identity to Vg of different penaeid species. Peptide mass fingerprints (PMFs) of the vitelline polypeptides suggest that the predicted endoprotease cleavage site at amino acids 725-728 does indeed undergo cleavage. Five prominent high-density lipoprotein polypeptides of masses 179, 113, 78, 61, and 42kDa were isolated from vitellogenic ovary, and their PMFs were determined by matrix-assisted laser desorption ionization time-of-flight (MALDI-TOF) spectrometry. It is likely that these polypeptides are all products of the LvVg gene. Removal of the X-organ sinus gland complex (XO-SG), which secretes the neurohormones that control the endocrine system regulating molt and reproduction, can induce both these processes. During the course of a number of molt cycles in induced sub-adult females, periodic ovarian growth and resorption were observed. Ovary growth correlated with LvVg expression in both the hepatopancreas and the ovary. Expression in ovaries of induced intermolt-early premolt females was significantly higher compared to all other sub-groups. Expression in ovaries of induced females was significantly higher compared to hepatopancreas at all molt cycle stages. Periodicity of molt and vitellogenesis in endocrinologically induced sub-adult shrimps may serve as a model to study alternate regulation of gene expression during these two processes.