Transcriptomic Analysis of the Kuruma Prawn Marsupenaeus japonicus Reveals Possible Peripheral Regulation of the Ovary

Chemical synthesis of insulin-like peptide 1 and its potential role in vitellogenesis of the kuruma prawn Marsupenaeus japonicus

The insulin superfamily comprises a group of peptides with diverse physiological functions and is conserved across the animal kingdom. Insulin-like peptides (ILPs) of crustaceans are classified into four major types: insulin, relaxin, gonadulin, and androgenic gland hormone (AGH)/insulin-like androgenic gland factor (IAG). Of these, the physiological functions of AGH/IAG have been clarified to be the regulation of male sex differentiation, but those of the other types have not been uncovered. In this study, we chemically synthesized Maj-ILP1, an ILP identified in the ovary of the kuruma prawn Marsupenaeus japonicus, using a combination of solid-phase peptide synthesis and regioselective disulfide bond formation reactions. As the circular dichroism spectral pattern of synthetic Maj-ILP1 is typical of other ILPs reported thus far, the synthetic peptide likely possessed the proper conformation. Functional analysis using ex vivo tissue incubation revealed that Maj-ILP1 significantly increased the expression of the yolk protein genes Maj-Vg1 and Maj-Vg2 in the hepatopancreas and Maj-Vg1 in the ovary of adolescent prawns. This is the first report on the synthesis of a crustacean ILP other than IAGs and also shows the positive relationship between the reproductive process and female-dominant ILP.

Ovarian transcriptome and metabolic responses of RNAi-mediated farnesyl pyrophosphate synthase knockdown in Neocaridina denticulata sinensis

Methyl farnesoate (MF) is considered the equivalent of JH in crustaceans and plays an essential role in many crucial physiological processes. It is believed that farnesyl pyrophosphate synthase (FPPS) plays an essential role in the biosynthesis of mevalonate, which is a branch of the JH/MF pathway. The full-length cDNA of FPPS (NdFPPS) from Neocaridina denticulata sinensis was isolated and characterized, and the deduced amino acid of NdFPPS contained a polyprenyl_synt domain. In addition to its ubiquitous tissue expression, NdFPPS was significantly expressed in the ovary. In vivo gene silencing with dsRNA interference was performed to further investigate the function of NdFPPS. An ovarian transcriptomic analysis of dsNdFPPS experimental and control groups was used to compare, annotate, and classify differentially expressed genes (DEGs). A total of 9230 DEGs were identified in the experimental and control groups based on FPKM values, of which 5082 were up-regulated genes and 4148 were down-regulated genes. 761 GO terms and 102 KEGG pathways were enriched for the DEGs. Our results suggest that NdFPPS might play an important role in ovarian development, however, further functional study is needed to elucidate physiological role of NdFPPS in reproduction.

A chromosome-level genome of the kuruma shrimp (Marsupenaeus japonicus) provides insights into its evolution and cold-resistance mechanism

Marsupenaeus japonicus is an important marine crustacean species. However, a lack of genomic resources hinders the use of whole genome sequencing to explore their genetic basis and molecular mechanisms for genome-assisted breeding. Consequently, we determined the chromosome-level genome of M. japonicus. Here we determine the chromosome-level genome assembly for M. japonicus with a total of 665.19 Gb genomic sequencing data, yielding an approximately1.54 Gb assembly with a contig N50 size of 229.97 kb and a scaffold N50 size of 38.27 Mb. With the high-throughput chromosome conformation capture (Hi-C) technology, we anchored 18,019 contigs onto 42 pseudo-chromosomes, accounting for 99.40% of the total genome assembly. Analysis of the present M. japonicus genome revealed 24,317 protein-coding genes and a high proportion of repetitive sequences (61.56%). The high-quality genome assembly enabled the identification of genes associated with cold-stress and cold tolerance in kuruma shrimp through the comparison of eyestalk transcriptomes between the low temperature-stressed shrimp (10 °C) and normal temperature shrimp (28 °C). The genome assembly presented here could be useful in future studies to reveal the molecular mechanisms of M. japonicus in response to low temperature stress and the molecular assisted breeding of M. japonicus in low temperature.

Potential receptors in Fenneropenaeus merguiensis ovary and role of saxophone, the bone morphogenetic protein receptor, in ovarian development

Receptors, which play an initial role in signaling pathways in several physiological processes, including reproduction, are among the several molecular factors that control ovarian development in organisms. This study aimed to identify and study receptors potentially involved in controlling the reproductive process of female banana shrimp, Fenneropenaeus merguiensis. Ovarian transcriptomes derived from 4 developmental stages were generated by RNA sequencing. A total of 53,763 transcripts were obtained from the de novo assembled transcriptome, and 663 genes were identified as receptors. Among them, 185 receptors were differentially expressed during ovarian development. Fifteen of these differentially expressed receptors showed distinct expression patterns that were validated by RT-qPCR. Bone morphogenetic protein receptors (BMPR) and their signaling genes were investigated for their roles in shrimp vitellogenesis. The expressions of F. merguiensis saxophone (FmSax), a BMP type I receptor, and BMP type II receptor (FmBMPRII) as well as FmMad, FmMed, and FmSMAD3 were significantly altered during ovarian development. RNA interference was used to investigate the role of FmSax in vitellogenesis. The result indicated that the expression of vitellogenin (Vg) was significantly reduced in both ovary and hepatopancreas of FmSax-knockdown shrimp compared to control shrimp. Furthermore, in FmSax-silencing shrimp, FmBMPRII, FmMad, and FmMed expressions were decreased as well as Vg expression. These findings suggest that FmSax positively regulates Vg synthesis via the BMP signaling pathway.

Recent advances in neuropeptide-related omics and gene editing: Spotlight on NPY and somatostatin and their roles in growth and food intake of fish

Feeding and growth are two closely related and important physiological processes in living organisms. Studies in mammals have provided us with a series of characterizations of neuropeptides and their receptors as well as their roles in appetite control and growth. The central nervous system, especially the hypothalamus, plays an important role in the regulation of appetite. Based on their role in the regulation of feeding, neuropeptides can be classified as orexigenic peptide and anorexigenic peptide. To date, the regulation mechanism of neuropeptide on feeding and growth has been explored mainly from mammalian models, however, as a lower and diverse vertebrate, little is known in fish regarding the knowledge of regulatory roles of neuropeptides and their receptors. In recent years, the development of omics and gene editing technology has accelerated the speed and depth of research on neuropeptides and their receptors. These powerful techniques and tools allow a more precise and comprehensive perspective to explore the functional mechanisms of neuropeptides. This paper reviews the recent advance of omics and gene editing technologies in neuropeptides and receptors and their progresses in the regulation of feeding and growth of fish. The purpose of this review is to contribute to a comparative understanding of the functional mechanisms of neuropeptides in non-mammalians, especially fish.

Growth trait gene analysis of kuruma shrimp (Marsupenaeus japonicus) by transcriptome study

Growth traits are a vital standard for the animal culture industry. The molecular mechanism of growth traits remains poorly understood, especially in aquaculture, which hinders the development of the selective breeding industry. Genomic resources discovered by next-generation sequencing (NGS) have been widely applied in certain species. However, accurate assembly and downstream analysis by NGS are still major challenges for species without reference genomes. In this study, a comparative transcriptome analysis of an economic crustacean species (Marsupenaeus japonicus) between a fast growth group and slow growth group at different stages was performed by SMRT (single molecule real time) and NGS. A high-quality full-length transcriptome (e.g., mean length of unigenes was longer than those unigenes assembled by Illumina clean reads from previous reports, and annotation rate was higher than Illumina sequencing in the same studies) was generated and analyzed. Several differentially expressed genes (DEGs) related to growth were identified and validated by quantitative real-time PCR (qPCR). The results showed that compared with the late stage, more DEGs were identified at the early stage, indicating that the growth-related physiological activity differences between different individuals at the early stage were higher than at the late stage. Moreover, 215 DEGs were shared between the early stage and late stage, and 109 had divergent functions during development. These 109 genes may play an important role in regulating the specific growth rate (SGR) of kuruma shrimp. In addition, twelve growth-related pathways were shared between the two comparative groups. Among these pathways, the fly Hippo signaling pathway and its key gene Mj14-3-3-like were identified for the first time to be involved in growth traits in crustaceans. Further analysis showed that Mj14-3-3-like was significantly downregulated in the fast growth group at the early stage and late stage; its expression level was reduced to its lowest level at the intermolt stage (C), the most important growth stage in shrimp, suggesting that Mj14-3-3-like may inhibit the growth of kuruma shrimp. Our study helps to elucidate the genes involved in the molecular mechanisms governing growth traits in kuruma shrimp, which is valuable for future shrimp developmental research.

Signaling Pathways That Regulate the Crustacean Molting Gland

A pair of Y-organs (YOs) are the molting glands of decapod crustaceans. They synthesize and secrete steroid molting hormones (ecdysteroids) and their activity is controlled by external and internal signals. The YO transitions through four physiological states over the molt cycle, which are mediated by molt-inhibiting hormone (MIH; basal state), mechanistic Target of Rapamycin Complex 1 (mTORC1; activated state), Transforming Growth Factor-β (TGFβ)/Activin (committed state), and ecdysteroid (repressed state) signaling pathways. MIH, produced in the eyestalk X-organ/sinus gland complex, inhibits the synthesis of ecdysteroids. A model for MIH signaling is organized into a cAMP/Ca2+-dependent triggering phase and a nitric oxide/cGMP-dependent summation phase, which maintains the YO in the basal state during intermolt. A reduction in MIH release triggers YO activation, which requires mTORC1-dependent protein synthesis, followed by mTORC1-dependent gene expression. TGFβ/Activin signaling is required for YO commitment in mid-premolt. The YO transcriptome has 878 unique contigs assigned to 23 KEGG signaling pathways, 478 of which are differentially expressed over the molt cycle. Ninety-nine contigs encode G protein-coupled receptors (GPCRs), 65 of which bind a variety of neuropeptides and biogenic amines. Among these are putative receptors for MIH/crustacean hyperglycemic hormone neuropeptides, corazonin, relaxin, serotonin, octopamine, dopamine, allatostatins, Bursicon, ecdysis-triggering hormone (ETH), CCHamide, FMRFamide, and proctolin. Contigs encoding receptor tyrosine kinase insulin-like receptor, epidermal growth factor (EGF) receptor, and fibroblast growth factor (FGF) receptor and ligands EGF and FGF suggest that the YO is positively regulated by insulin-like peptides and growth factors. Future research should focus on the interactions of signaling pathways that integrate physiological status with environmental cues for molt control.