Temporal silencing of an androgenic gland-specific insulin-like gene affecting phenotypical gender differences and spermatogenesis

Crustacean sexual differentiation: a decapod perspective

Sexual differentiation in crustaceans is shaped by genetic, hormonal, and environmental factors, with notable interspecies diversity. This review highlights key mechanisms in decapods, including genetic pathways like Doublesex and species-specific variations, such as the Y-linked iDMY gene in spiny lobsters. Male differentiation is driven by the androgenic gland and its insulin-like hormone, while female differentiation involves eyestalk neuropeptides like gonad-inhibiting hormone. Environmental factors, such as density, influence flexible genetic systems. These findings aid aquaculture by enabling sex ratio manipulation and inform conservation through biotechnological advances. Emerging tools like CRISPR promise deeper insights into crustacean sexual differentiation.

Gonadal transcriptome analysis reveals MAG participates in ovarian suppression of intersex red claw crayfish (Cherax quadricarinatus)

BACKGROUND

The red claw crayfish (Cherax quadricarinatus) is a commercially and ecologically significant species that displays a unique intersex model with an ovotestis gonad and was identified to have functional testes and a vestigial ovary, which was inhibited by insulin-like androgenic gland hormone (IAG), but the underlying molecular mechanisms are still unclear.

RESULTS

In this study, the structure and transcriptomic profiles of ovotestis and female and male gonad was analysis and compared, 406 differentially expressed genes were identified, among which membrane-anchored AG-specific factor (MAG) exhibited significantly greater expression in ovotestis gonads than in male or female gonads. The localization of MAG in type I or II cells of androgenic gland revealed its potential function of IAG hormone synthesis. Furthermore, the analyses of gene regulation relationship revealed that IAG positively regulates MAG expression, while MAG negatively regulates vitellogenin gene (VTG) expression.

CONCLUSIONS

Our research suggesting MAG participates in the IAG regulated ovarian suppression in the intersex red claw crayfish, which provides important information on the regulatory mechanism of the ovarian dysplasia in the ovotestis of intersex red claw crayfish. These results will enhance the knowledge of IAG-related pathways in the female reproductive axis, as well as the mechanisms of sexual differentiation in crustaceans.

Crustacean endocrinology: Sexual differentiation and potential application for aquaculture

Crustaceans, which represent a significant subset of arthropods, are classified into three major classes: Ostracoda, Malacostraca, and Branchiopoda. Among them, sex manipulation in decapod species from the Malacostraca class has been extensively researched for aquaculture purposes and to study reproductive physiology and sexual plasticity. Some decapods exhibit sexual dimorphism that influences their biological and economic value. Monosex culture, in which only one sex is cultivated, increases production yields while reducing the risk of invasiveness, as genetic leakage into natural waters is less likely to occur. Differences in yield are also observed when cultivating different sexes, with all-male cultures of Macrobrachium rosenbergii being more profitable than both mixed and all-female cultures. Research on decapod sexual differentiation has led to a better understanding of sex determination and sexual differentiation processes in arthropods. Similar to most mammals and other vertebrate classes, Malacostraca crustaceans, including decapods, exhibit a cell-non-autonomous mode of sexual development. Genetic factors (e.g., sex chromosomes) and endocrine factors (e.g., insulin-like androgenic gland factor and crustacean female sex hormone) play pivotal roles in the development of sexually dimorphic traits. This review synthesizes the existing understanding of sex determination mechanisms and the role of sex hormones in decapod species. Additionally, it provides an overview of the methyl farnesoate, which has been suggested to be involved in male sex differentiation in some crab species, as well as the phenomenon of male-to-female sex reversal in host decapods caused by parasitic crustaceans.

A brief and updated introduction to the neuroendocrine system of crustaceans

The neuroendocrine system of crustaceans is complex and regulates many processes, such as development, growth, reproduction, osmoregulation, behavior, and metabolism. Once stimulated, crustaceans' neuroendocrine tissues modulate the release of monoamines, ecdysteroids, and neuropeptides that can act as hormones or neurotransmitters. Over a few decades, research has unraveled some mechanisms governing these processes, substantially contributing to understanding crustacean physiology. More aspects of crustacean neuroendocrinology are being comprehended with molecular biology, transcriptome, and genomics analyses. Hence, these studies will also significantly enhance the ability to cultivate decapods, such as crabs and shrimps, used as human food sources. In this review, current knowledge on crustacean endocrinology is updated with new findings about crustacean hormones, focusing mainly on the main neuroendocrine organs and their hormones and the effects of these molecules regulating metabolism, growth, reproduction, and color adaptation. New evidence about vertebrate-type hormones found in crustaceans is included and discussed. Finally, this review may assist in understanding how the emerging chemicals of environmental concern can potentially impair and disrupt crustacean's endocrine functions and their physiology.

A new type II CHH neuropeptide involves ovarian development in the peppermint shrimp, Lysmata vittata

Type II crustacean hyperglycemic hormone (CHH) neuropeptides play diverse roles in crustaceans. In the hermaphrodite shrimp Lysmata vittata, two transcripts of type II CHHs (molt-inhibiting hormone/gonad-inhibiting hormone, MIH/GIH1 and MIH/GIH2) were identified by transcriptome sequencing, and MIH/GIH1 was later named Lvit-GIH1 for its inhibitory effect on ovarian development. Based on the high similarity of MIH/GIH2 to Lvit-GIH1, we named tentatively MIH/GIH2 as Lvit-GIH2 and explored the role of Lvit-GIH2 in ovarian development. The open reading frame (ORF) of Lvit-GIH2 was 333 bp in length, encoding a precursor consisted of a 32-aa signal peptide and a 78-aa mature peptide, which shared high sequence similarity with the type II subfamily peptides in crustaceans. Notably, Lvit-GIH2 was widely expressed in multiple tissues. The qRT-PCR findings indicated a rising trend in the expression of Lvit-GIH2 from the male phase to the euhermaphrodite phase. Both RNA interference and addition of GIH2 recombinant proteins (rGIH2) experiments showed that Lvit-GIH2 suppressed Lvit-Vg expression in hepatopancreas and Lvit-VgR expression in ovary. To further investigate the role of Lvit-GIH2 in ovarian development, the RNA-sequence analysis was performed to examine the changes in ovary after addition of rGIH2. The results showed that the pathways (Cysteine and methionine metabolism, Apoptosis-multiple species, etc.) and the genes (17bHSD8, IGFR, CHH, etc.) related to ovarian development were negatively regulated by rGIH2. In brief, Lvit-GIH2 might inhibit the ovarian development in L. vittata.

A Testis-Specific DMRT1 (Double Sex and Mab-3-Related Transcription Factor 1) Plays a Role in Spermatogenesis and Gonadal Development in the Hermaphrodite Boring Giant Clam Tridacna crocea

The testis-specific double sex and mab-3-related transcription factor 1 (DMRT1) has long been recognized as a crucial player in sex determination across vertebrates, and its essential role in gonadal development and the regulation of spermatogenesis is well established. Here, we report the cloning of the key spermatogenesis-related DMRT1 cDNA, named Tc-DMRT1, from the gonads of Tridacna crocea (T. crocea), with a molecular weight of 41.93 kDa and an isoelectric point of 7.83 (pI). Our hypothesis is that DMRT1 machinery governs spermatogenesis and regulates gonadogenesis. RNAi-mediated Tc-DMRT1 knockdown revealed its critical role in hindering spermatogenesis and reducing expression levels in boring giant clams. A histological analysis showed structural changes, with normal sperm cell counts in the control group (ds-EGFP) but significantly lower concentrations of sperm cells in the experimental group (ds-DMRT1). DMRT1 transcripts during embryogenesis exhibited a significantly high expression pattern (p < 0.05) during the early zygote stage, and whole-embryo in-situ hybridization confirmed its expression pattern throughout embryogenesis. A qRT-PCR analysis of various reproductive stages revealed an abundant expression of Tc-DMRT1 in the gonads during the male reproductive stage. In-situ hybridization showed tissue-specific expression of DMRT1, with a positive signal detected in male-stage gonadal tissues comprising sperm cells, while no signal was detected in other stages. Our study findings provide an initial understanding of the DMRT1 molecular machinery controlling spermatogenesis and its specificity in male-stage gonads of the key bivalve species, Tridacna crocea, and suggest that DMRT1 predominantly functions as a key regulator of spermatogenesis in giant clams.

Considerations for cultivated crustacean meat: potential cell sources, potential differentiation and immortalization strategies, and lessons from crustacean and other animal models

Cultivated crustacean meat (CCM) is a means to create highly valued shrimp, lobster, and crab products directly from stem cells, thus removing the need to farm or fish live animals. Conventional crustacean enterprises face increasing pressures in managing overfishing, pollution, and the warming climate, so CCM may provide a way to ensure sufficient supply as global demand for these products grows. To support the development of CCM, this review briefly details crustacean cell culture work to date, before addressing what is presently known about crustacean muscle development, particularly the molecular mechanisms involved, and how this might relate to recent work on cultivated meat production in vertebrate species. Recognizing the current lack of cell lines available to establish CCM cultures, we also consider primary stem cell sources that can be obtained non-lethally including tissues from limbs which are readily released and regrown, and putative stem cells in circulating hemolymph. Molecular approaches to inducing myogenic differentiation and immortalization of putative stem cells are also reviewed. Finally, we assess the current status of tools available to CCM researchers, particularly antibodies, and propose avenues to address existing shortfalls in order to see the field progress.

Identification of Candidate Male-Reproduction-Related Genes from the Testis and Androgenic Gland of Macrobrachium nipponense, Regulated by PDHE1, through Transcriptome Profiling Analysis

The previous publication identified that pyruvate dehydrogenase E1 (PDHE1) positively regulated the process of male reproduction in M. nipponense through affecting the expressions of insulin-like androgenic gland hormone. The present study aimed to identify the potential male-reproduction-related genes that were regulated by PDHE1 through performing the transcriptome profiling analysis in the testis and androgenic gland after the knockdown of the expressions of PDHE1 by the injection of dsPDHE1. Both RNA-Seq and qPCR analysis identified the significant decreases in PDHE1 expressions in the testis and androgenic gland in dsPDHE1-injected prawns compared to those in dsGFP-injected prawns, indicating the efficiency of dsPDHE1 in the present study. Transcriptome profiling analysis identified 56 and 127 differentially expressed genes (DEGs) in the testis and androgenic gland, respectively. KEGG analysis revealed that the energy-metabolism-related pathways represented the main enriched metabolic pathways of DEGs in both the testis and androgenic gland, including pyruvate metabolism, the Citrate cycle (TCA cycle), Glycolysis/Gluconeogenesis, and the Glucagon signaling pathway. Thus, it is predicted that these metabolic pathways and the DEGs from these metabolic pathways regulated by PDHE1 may be involved in the regulation of male reproduction in M. nipponense. Furthermore, four genes were found to be differentially expressed in both the testis and androgenic gland, of which ribosomal protein S3 was down-regulated and uncharacterized protein LOC113829596 was up-regulated in both the testis and androgenic gland in dsPDHE1-injected prawns. The present study provided valuable evidence for the establishment of an artificial technique to regulate the process of male reproduction in M. nipponense.

Role of Mn-LIPA in Sex Hormone Regulation and Gonadal Development in the Oriental River Prawn, Macrobrachium nipponense

This study investigates the role of lysosomal acid lipase (LIPA) in sex hormone regulation and gonadal development in Macrobrachium nipponense. The full-length Mn-LIPA cDNA was cloned, and its expression patterns were analyzed using quantitative real-time PCR (qPCR) in various tissues and developmental stages. Higher expression levels were observed in the hepatopancreas, cerebral ganglion, and testes, indicating the potential involvement of Mn-LIPA in sex differentiation and gonadal development. In situ hybridization experiments revealed strong Mn-LIPA signaling in the spermatheca and hepatopancreas, suggesting their potential role in steroid synthesis (such as cholesterol, fatty acids, cholesteryl ester, and triglycerides) and sperm maturation. Increased expression levels of male-specific genes, such as insulin-like androgenic gland hormone (IAG), sperm gelatinase (SG), and mab-3-related transcription factor (Dmrt11E), were observed after dsMn-LIPA (double-stranded LIPA) injection, and significant inhibition of sperm development and maturation was observed histologically. Additionally, the relationship between Mn-LIPA and sex-related genes (IAG, SG, and Dmrt11E) and hormones (17β-estradiol and 17α-methyltestosterone) was explored by administering sex hormones to male prawns, indicating that Mn-LIPA does not directly control the production of sex hormones but rather utilizes the property of hydrolyzing triglycerides and cholesterol to provide energy while influencing the synthesis and secretion of self-sex hormones. These findings provide valuable insights into the function of Mn-LIPA in M. nipponense and its potential implications for understanding sex differentiation and gonadal development in crustaceans. It provides an important theoretical basis for the realization of a monosex culture of M. nipponense.

Transcriptional regulation of IAG by dsx and foxl-2 in mud crab (Scylla paramamosain)

Scylla paramamosain is an important cultured crab species on the southeast coast of China. However, the molecular regulation mechanism of its gonadal development still has not been thoroughly studied. Dsx (doublesex) and foxl-2 (forkhead transcription factor gene 2) are important transcription factors involved in gonadal development. So far, studies on the functions of dsx and foxl-2 in crustaceans are very limited. Insulin-like androgenic gland hormone (IAG) is an effector molecule that regulates the differentiation, development and sex maintenance of testes in crustaceans. In this study, the promoter region of Sp-IAG was predicted, and several potential binding sites of dsx and foxl-2 were found. Site-directed mutagenesis was performed on the predicted potential binding sites, and their promoter activity was analyzed. The results showed that there was a dsx and a foxl-2 binding site, respectively, that could regulate the expression of Sp-IAG. In order to verify the regulatory effect of these two transcription factors on Sp-IAG, we constructed the expression plasmids of dsx and foxl-2 and co-transfected them into HEK293T cell lines with the promoter of Sp-IAG, respectively. The results showed that dsx could significantly promote the expression of Sp-IAG, while foxl-2 could inhibit its expression substantially. Then we carried out in vivo RNA interference experiment on mud crabs. The expression of dsx and foxl-2 in crabs was interfered respectively. The results of qRT-PCR showed that the expression of Sp-IAG was significantly inhibited after interfering with dsx, while significantly increased after interfering with foxl-2, which was consistent with the cell experiment. In conclusion, dsx and foxl-2 transcription factors play opposite roles in regulating the expression of Sp-IAG.

Monosex Populations of the Giant Freshwater Prawn Macrobrachium rosenbergii-From a Pre-Molecular Start to the Next Generation Era

Sexual manipulation in the giant freshwater prawn Macrobrachium rosenbergii has proven successful in generating monosex (both all-male and all-female) populations for aquaculture using a crustacean-specific endocrine gland, the androgenic gland (AG), which serves as a key masculinizing factor by producing and secreting an insulin-like AG hormone (IAG). Here, we provide a summary of the advancements from the discovery of the AG and IAG in decapods through to the development of monosex populations in M. rosenbergii. We discuss the broader sexual development pathway, which is highly divergent across decapods, and provide our future perspective on the utility of novel genetic and genomic tools in promoting refined approaches towards monosex biotechnology. Finally, the future potential benefits of deploying monosex prawn populations for environmental management are discussed.

Analysis of mRNA and MicroRNA Expression Profiles of Nervous Tissues and Reproductive Tissues in Male Procambarus clarkii After Silencing IAG

The insulin-like androgenic gland hormone gene (IAG), primarily expressed in the androgenic gland (AG), plays a crucial role in controlling male sex differentiation and maintaining male secondary sexual characteristics in decapods. In this study, we investigated the mRNA and microRNA expression profiles of male Procambarus clarkii to understand the transcriptomic regulatory mechanism of IAG after the injection of an efficient siRNA (GsiRNA) designed based on IAG. The results revealed that several differentially expressed genes were enriched in reproduction-related pathways, such as the wnt signaling pathway, MAPK signaling pathway, and GnRH signaling pathway. In the testis (Te), the injection of GsiRNA led to the up-regulation of many ovary-related genes and down-regulation of testis-related genes. Moreover, the brain (Br) and abdominal nerve cord (AN) appeared to be involved in the regulation of IAG, with numerous differentially expressed genes found in Br and AN. Notably, the expression of five neuropeptide genes, Crustacean hyperglycemic hormone, pigment-dispersing hormone, red pigment concentrating hormone precursor, corazonin, and gonadotropin-releasing hormone II receptor isoform X1 in Br/AN, was significantly changed. Additionally, three ovary-related miRNAs (miR-263a, miR-263b, miR-133) highly expressed in Te/AG showed significant up-regulation after GsiRNA injection. Furthermore, the long-term interference of GsiRNA was found to inhibit the development of male external sexual characteristics during the juvenile stage and delay it during the adult stage. This research provides valuable insights into the molecular regulatory mechanism and function of IAG in P. clarkii.

Identification of Crustacean Female Sex Hormone Receptor Involved in Sexual Differentiation of a Hermaphroditic Shrimp

The neurohormone crustacean female sex hormone (CFSH) contains a highly conserved interleukin-17 (IL-17) domain in the mature peptide. Although CFSH has been demonstrated to stimulate female sexual differentiation in crustaceans, its receptors (CFSHR) have been poorly reported. The present study identified an IL-17 receptor (named Lvit-IL-17R), a candidate of CFSHR, from the protandric simultaneous hermaphroditic (PSH) shrimp Lysmata vittata through GST pulldown assays and RNAi experiments. Lvit-IL-17R is a transmembrane protein with an SEFIR (similar expression as the fibroblast growth factor and IL-17R) domain, as determined through sequence analysis. A GST pulldown experiment confirmed the interactions between the type I CFSHs (CFSH1a and CFSH1b) and Lvit-IL-17R. Meanwhile, the RNAi results revealed that Lvit-IL-17R displays similar functions to type I CFSHs in regulating sexual differentiation and gonad development. In brief, Lvit-IL-17R is a potential receptor for type I CFSHs aimed at regulating the sexual differentiation of the PSH species. This study helps shed new light on the mechanism of sexual differentiation among crustaceans.

Insulin-like Androgenic Gland Hormone Induced Sex Reversal and Molecular Pathways in Macrobrachium nipponense: Insights into Reproduction, Growth, and Sex Differentiation

This study investigated the potential to use double-stranded RNA insulin-like androgenic gland hormone (dsIAG) to induce sex reversal in Macrobrachium nipponense and identified the molecular mechanisms underlying crustacean reproduction and sex differentiation. The study aimed to determine whether dsIAG could induce sex reversal in PL30-male M. nipponense during a critical period. The sex-related genes were selected by performing the gonadal transcriptome analysis of normal male (dsM), normal female (dsFM), neo-female sex-reversed individuals (dsRM), and unreversed males (dsNRM). After six injections, the experiment finally resulted in a 20% production of dsRM. Histologically, dsRM ovaries developed slower than dsFM, but dsNRM spermathecae developed normally. A total of 1718, 1069, and 255 differentially expressed genes were identified through transcriptome sequencing of the gonads in three comparison groups, revealing crucial genes related to reproduction and sex differentiation, such as GnRHR, VGR, SG, and LWS. Principal Component Analysis (PCA) also distinguished dsM and dsRM very well. In addition, this study predicted that the eyestalks and the "phototransduction-fly" photoperiodic pathways of M. nipponense could play an important role in sex reversal. The enrichment of related pathways and growth traits in dsNRM were combined to establish that IAG played a significant role in reproduction, growth regulation, and metabolism. Finally, complete sex reversal may depend on specific stimuli at critical periods. Overall, this study provides valuable findings for the IAG regulation of sex differentiation, reproduction, and growth of M. nipponense in establishing a monoculture.

Isolation of an Insulin-Like Receptor Involved in the Testicular Development of the Mud Crab Scylla paramamosain

Insulin-like androgenic gland hormone (IAG) is a key regulator of male sexual differentiation in crustaceans that plays important roles in secondary sexual characteristics and testicular development. As a hormone, IAG interacts with its membrane receptor to initiate downstream signal pathways to exert its biological functions. In this study, we isolated a full-length cDNA of an insulin-like receptor (Sp-IR) from the mud crab Scylla paramamosain. Sequence analysis revealed that this receptor consists of a Fu domain, two L domains, three FN-III domains, a transmembrane domain, and a tyrosine kinase domain, classifying it as a member of the tyrosine kinase insulin-like receptors family. Our results also suggested that Sp-IR was highly expressed in the testis and AG in males. Its expression in the testis peaked in stage I but significantly decreased in stages II and III (p < 0.01). Next, both short- and long-term RNA interference (RNAi) experiments were performed on males in stage I to explore Sp-IR function in mud crabs. The results showed that Sp-vasa and Sp-Dsx expression levels in the testis were significantly down-regulated after the specific knockdown of Sp-IR by RNAi. Additionally, the long-term knockdown of Sp-IR led to a considerable decrease in the volume of seminiferous tubules, accompanied by large vacuoles and a reduced production of secondary spermatocytes and spermatids. In conclusion, our results indicated that Sp-IR is involved in testicular development and plays a crucial role in transitioning from primary to secondary spermatocytes. This study provided a molecular basis for the subsequent analysis of the mechanism on male sexual differentiation in Brachyuran crabs.

Identification of Male Sex-Related Genes Regulated by SDHB in Macrobrachium nipponense Based on Transcriptome Analysis after an RNAi Knockdown

The oriental river prawn (Macrobrachium nipponense) is a commercially important species in Asia. A previous study showed that the succinate dehydrogenase complex iron sulfur subunit B (SDHB) gene participates in testes development in this species through its effect on the expression of the insulin-like androgenic gland hormone gene. This study knocked-down the Mn-SDHB genes in M. nipponense using RNAi. A transcriptome analysis of the androgenic gland and testes was then performed to discover the male sex-related genes regulated by SDHB and investigate the mechanism of male sexual development in this species. More than 16,623 unigenes were discovered in each sample generated. In the androgenic gland, most of the differentially expressed genes were enriched in the hypertrophic cardiomyopathy pathway, while in the testes, they were enriched in the citrate cycle pathway. In addition, after Mn-SDHB knockdown, five genes were found to be downregulated in the androgenic gland in a series of biological processes associated with phosphorylated carbohydrate synthesis and transformations in the glycolysis/gluconeogenesis pathway. Moreover, a total of nine male sex-related genes were identified including Pro-resilin, insulin-like androgenic gland hormone, Protein mono-ADP-ribosyltransferase PAPR11, DNAJC2, C-type Lectin-1, Tyrosine-protein kinase Yes, Vigilin, and Sperm motility kinase Y-like, demonstrating the regulatory effects of Mn-SDHB, and providing a reference for the further study of the mechanisms of male development in M. nipponense.

Identification of a Putative CFSH Receptor Inhibiting IAG Expression in Crabs

The crustacean female sex hormone (CFSH) is a neurohormone peculiar to crustaceans that plays a vital role in sexual differentiation. This includes the preservation and establishment of secondary female sexual traits, as well as the inhibition of insulin-like androgenic gland factor (IAG) expression in the androgenic gland (AG). There have been no reports of CFSH receptors in crustaceans up to this point. In this study, we identified a candidate CFSH receptor from the mud crab Scylla paramamosain (named Sp-SEFIR) via protein interaction experiments and biological function experiments. Results of GST pull-down assays indicated that Sp-SEFIR could combine with Sp-CFSH. Findings of in vitro and in vivo interference investigations exhibited that knockdown of Sp-SEFIR could significantly induce Sp-IAG and Sp-STAT expression in the AG. In brief, Sp-SEFIR is a potential CFSH receptor in S. paramamosain, and Sp-CFSH controls Sp-IAG production through the CFSH-SEFIR-STAT-IAG axis.

The transcription factor masculinizer in sexual differentiation and achieved full functional sex reversal in prawn

Some Zinc finger (ZnF) proteins are required for masculinization in silkworms. In the present study, a masculinizer gene (Mr-Masc) with multi-tissue expression is identified in the freshwater prawn Macrobrachium rosenbergii. The Mr-Masc is clustered into a separate branch with ZnF proteins from decapoda by phylogenetic tree analysis. Moreover, Mr-Masc silencing in male postlarvae prawn results in functional sex reversal females known as neo-females, which are applied to all-male monosex offspring breeding. This manipulation has been significant in sexually dimorphic cultured species. In addition, several significantly expressed transcripts are enriched and the effects of crucial signal pathways are focused through the comparative transcriptomic analysis in Mr-Masc gene knockdown. The significantly differentially expressed epidermal growth factor, upregulated low-density lipoprotein receptor, flotillin, and sex-lethal unigenes, downregulated heat shock proteins and forkhead box homologs are focused. The finding offers an innovative perspective on Masc proteins' evolution and physiological function.

Crustacean female sex hormone: More than a female phenotypes-related hormone in a protandric simultaneous hermaphroditism shrimp

Crustacean female sex hormone (CFSH) is believed to regulate the development of female-related phenotypes in crustaceans. However, its role in gonadal development has been understudied. This study identified a CFSH gene, Lvit-CFSH1b, in the peppermint shrimp Lysmata vittata, a protandric simultaneous hermaphroditism (PSH) species. Lvit-CFSH1b is only expressed in the eyestalk ganglion. qRT-PCR showed that the expression level of Lvit-CFSH1b significantly increased with the gonad development from stage I to III (male phase) and decreased at stage IV (euhermaphrodite phase). Gene knockdown of Lvit-CFSH1b resulted in retardation of female phenotypes and stimulated the development of male phenotypes. At the same time, ovarian development was inhibited, and spermatogenesis was promoted. In addition, injection of rCFSH1b increased ovarian expression of vitellogenin (Lvit-Vg) and hepatopancreas expression of vitellogenin receptor (Lvit-VgR), while suppressing the expressions of insulin-like androgenic gland hormones (Lvit-IAG1 and Lvit-IAG2) in androgenic glands. The addition of rCFSH1b induced the in vitro expression of Lvit-Vg in ovarian and Lvit-VgR in hepatopancreas explants. In conclusion, this study provides convincing evidence that CFSH expedites the feminization process and impedes masculinization by inhibiting IAG in hermaphroditic crustaceans.

IAG Regulates the Expression of Cytoskeletal Protein-Encoding Genes in Shrimp Testis

Insulin-like androgenic gland hormone (IAG) is the master regulator of sexual differentiation and testis development in male crustaceans. However, the molecular mechanism on how IAG functions during testis development is still largely unknown. Here, the transcriptional changes were analyzed in the testes of shrimp after LvIAG knockdown in Litopenaeus vannamei. Differential expression analysis identified 111 differentially expressed genes (DEGs), including 48 upregulated DEGs and 63 downregulated DEGs, in testes of shrimp after LvIAG knockdown. Gene ontology (GO) analysis showed that these DEGs were apparently enriched in cytoskeleton-related GO items. Gene function analysis showed that genes enriched in these GO items mainly encoded actin, myosin, and heat shock protein. Interestingly, these genes were all downregulated in testis after LvIAG knockdown, which was confirmed by qRT-PCR detection. Furthermore, injection of LvIAG protein that was recombinantly expressed in insect cells upregulated the expression levels of these genes. The present study revealed that shrimp IAG might function in testis development through regulating the expression of cytoskeletal protein-encoding genes, which would provide new insights into understanding the functional mechanisms of IAG on male sexual development of crustaceans.

Unravelling the neuropeptidome of the ornate spiny lobster Panulirus ornatus: A focus on peptide hormones and their processing enzymes expressed in the reproductive tissues

Neuropeptides are commonly produced in the neural tissues yet can have effects on far-reaching targets, with varied biological responses. We describe here the neuropeptidome of the ornate spiny lobster, Panulirus ornatus, a species of emerging importance to closed-system aquaculture, with a focus on peptide hormones produced by the reproductive tissues. Transcripts for a precursor to one neuropeptide, adipokinetic hormone/corazonin-related peptide (ACP) were identified in high numbers in the sperm duct of adult spiny lobsters suggesting a role for ACP in the reproduction of this species. Neuropeptide production in the sperm duct may be linked with physiological control of spermatophore production in the male, or alternatively may function in signalling to the female. The enzymes which process nascent neuropeptide precursors into their mature, active forms have seldom been studied in decapods, and never before at the multi-tissue level. We have identified transcripts for multiple members of the proprotein convertase subtisilin/kexin family in the ornate spiny lobster, with some enzymes showing specificity to certain tissues. In addition, other enzyme transcripts involved with neuropeptide processing are identified along with their tissue and life stage expression patterns.

The insulin signaling pathway a century after its discovery: Sexual dimorphism in insulin signaling

Since practically a century ago, the insulin pathway was discovered in both vertebrates and invertebrates, implying an evolutionarily ancient origin. After a century of research, it is now clear that the insulin signal transduction pathway is a critical, flexible and pleiotropic pathway, evolving into multiple anabolic functions besides glucose homeostasis. It regulates paramount aspects of organismal well-being like growth, longevity, intermediate metabolism, and reproduction. Part of this diversification has been attained by duplications and divergence of both ligands and receptors riding on a common general signal transduction system. One of the aspects that is strikingly different is its usage in reproduction, particularly in male versus female development and fertility within the same species. This review highlights sexual divergence in metabolism and reproductive tract differences, the occurrence of sexually "exaggerated" traits, and sex size differences that are due to the sexes' differential activity/response to the insulin signaling pathway.

Identification and Expression Analysis of Dsx and Its Positive Transcriptional Regulation of IAG in Black Tiger Shrimp (Penaeus monodon)

Doublesex (Dsx) is a polymorphic transcription factor of the DMRTs family, which is involved in male sex trait development and controls sexual dimorphism at different developmental stages in arthropods. However, the transcriptional regulation of the Dsx gene is largely unknown in decapods. In this study, we reported the cDNA sequence of PmDsx in Penaeus monodon, which encodes a 257 amino acid polypeptide. It shared many similarities with Dsx homologs and has a close relationship in the phylogeny of different species. We demonstrated that the expression of the male sex differentiation gene Dsx was predominantly expressed in the P. monodon testis, and that PmDsx dsRNA injection significantly decreased the expression of the insulin-like androgenic gland hormone (IAG) and male sex-determining gene while increasing the expression of the female sex-determining gene. We also identified a 5′-flanking region of PmIAG that had two potential cis-regulatory elements (CREs) for the PmDsx transcription. Further, the dual-luciferase reporter analysis and truncated mutagenesis revealed that PmDsx overexpression significantly promoted the transcriptional activity of the PmIAG promoter via a specific CRE. These results suggest that PmDsx is engaged in male reproductive development and positively regulates the transcription of the PmIAG by specifically binding upstream of the promoter of the PmIAG. It provides a theoretical basis for exploring the sexual regulation pathway and evolutionary dynamics of Dmrt family genes in P. monodon.

CRISPR/Cas9-mediated mutation on an insulin-like peptide encoding gene affects the growth of the ridgetail white prawn Exopalaemon carinicauda

Insulin-like peptides (ILPs) play key roles in animal growth, metabolism and reproduction in vertebrates. In crustaceans, one type of ILPs, insulin-like androgenic gland hormone (IAG) had been reported to be related to the sex differentiations. However, the function of other types of ILPs is rarely reported. Here, we identified another type of ILPs in the ridgetail white prawn Exopalaemon carinicauda (EcILP), which is an ortholog of Drosophila melanogaster ILP7. Sequence characterization and expression analyses showed that EcILP is similar to vertebrate insulin/IGFs and insect ILPs in its heterodimeric structure and expression profile. Using CRISPR/Cas9 genome editing technology, we generated EcILP knockout (KO) prawns. EcILP-KO individuals have a significant higher growth-inhibitory trait and mortality than those in the normal group. In addition, knockdown of EcILP by RNA interference (RNAi) resulted in slower growth rate and higher mortality. These results indicated that EcILP was an important growth regulator in E. carinicauda.

Transcriptome analysis of the post-larvae of giant freshwater prawn (Macrobrachium rosenbergii) after IAG gene knockdown with microRNA interference

The insulin-like androgenic gland hormone gene (IAG) of crustaceans plays pivotal roles in the regulation of sex differentiation. MicroRNAs (miRNAs) are a class of short, non-coding RNAs that function as post-transcriptional gene regulators. However, little information about the regulatory relationship between miRNA and Macrobrachium rosenbergii IAG (MrIAG) were exposed. In this study, we used the 3' untranslated region (UTR) of MrIAG to predict potential target sites of miRNAs. The results showed that miR-184 has one target site in the 3'UTR of MrIAG. Dual-luciferase report assay in vitro confirmed that miR-184 can significantly down-regulate MrIAG expression. Besides, we constructed mutant plasmids of 3'UTR of MrIAG. The result displayed that after co-transfection of mutant plasmids and miR-184 agomir, the activity of luciferase was not affected compared to the control. These results indicated that miR-184 could directly regulate MrIAG. In addition, we found that overexpression of miR-184 in M. rosenbergii can lead to significant changes in the transcription level of genes. Compared with control group, we identified 1510 differentially expressed genes (DEGs) in the miR-184 injection group. Some DEGs were involved in sex differentiation, gonad development, growth and molting were found. qRT-PCR verification was performed on eight DEGs randomly, and the results showed that the expression level of sex-, growth-, and metabolism-related genes changed significantly after MrIAG gene knockdown. Collectively, findings from this study suggest that miR-184, by mediating IAG expression, may be involved in many physiological processes in M. rosenbergii. The current study lays a basic understanding for short-term silencing of MrIAG with miR-184, and facilitates miRNA function analysis in M. rosenbergii in future.

Comparative transcriptome analysis of brain and gonad reveals reproduction-related miRNAs in the giant prawn, Macrobrachium rosenbergii

Macrobrachium rosenbergii (M. rosenbergii), as a species of common prawn, is a delicacy that is consumed all over the world. By interacting with the target gene 3′-untranslated region (3'-UTR), microRNAs (miRNAs) regulate its expression and ultimately participate in the regulation of reproductive development. However, research focusing on miRNA regulation during gonadal development in M. rosenbergii received very little attention. To explore the association between miRNA and reproduction, we performed RNA sequencing (RNA-seq) on brain and gonad organs in male and female M. rosenbergii. A total of 494 miRNAs were obtained in RNA-seq, including 31 and 59 differentially expressed (DE) miRNAs in the brain and gonads, respectively. Furthermore, 9 DE miRNAs were randomly selected from the brain and gonads, and qRT-PCR was conducted to validate the results of RNA-seq. Interestingly, dpu-miR-133 was found to be substantially expressed in the male brain and testis but poorly expressed in the female brain, ovary, and other organs. Analysis of dpu-miR-133 by Targetscan and MiRanda predicted to target 5-HT1. Furthermore, the dual-luciferase reporter assay manifested that dpu-miR-133 can combine with 5-HT1. Overall, our research work provides basic data for further study on the miRNA-mediated regulation of brain, gonad, and reproductive development of study M. rosenbergii.

17β-Estradiol (E2) may be involved in the mode of crustacean female sex hormone (CFSH) action in the blue crab, Callinectes sapidus

17β-estradiol (E2) has been proved to control reproduction, sexual differentiation, and the development of the secondary sexual characteristics of vertebrate females. In decapod crustacean species, crustacean female sex hormone (CFSH), a protein hormone, is required for developing adult-specific ovigerous setae for embryo brooding and gonophores for mating at the blue crab Callinectes sapidus puberty molting. However, it is unclear that whether the mode of CFSH action involves a vertebrate-type sex steroid hormone in crustaceans. To this end, E2 levels were first measured using a competitive ELISA in the hemolymph and the potential CFSH target tissues from both prepuberty and adult females; the presence of E2 was further confirmed with a liquid chromatography tandem mass spectrometry method. Then, the cDNAs of the following genes known to be associated with vertebrate steroidogenic pathways were isolated: StAR-related lipid transfer protein 3 (StAR3); 3β-hydroxysteroid dehydrogenase (3βHSD); two isoforms of 17β-hydroxysteroid dehydrogenase 8 (17βHSD8); and, estradiol-related receptor (ERR). RT-PCR analysis revealed that these genes were widely distributed in the eyestalk ganglia, hepatopancreas, brain, ovary, spermathecae, ovigerous and plumose setae tissues of adult females. The 17βHSD8 transcripts were localized in the follicle cells, the periphery of the nuclear membrane of primary oocytes, and yolk granules of the vitellogenic oocytes using in situ hybridization, and the corresponding protein was detected in the follicle cells and ooplasm of primary oocytes using immunohistochemistry. Furthermore, the adult females injected with CFSH-dsRNA (n = 30 times) had E2 and StAR3 transcripts levels lower in the ovigerous and plumose setae, spermathecae than controls. These results suggested that the mode of CFSH action in C. sapidus might involve E2 in these adult-female-specific tissues.

Comparative Transcriptomics of Gonads Reveals the Molecular Mechanisms Underlying Gonadal Development in Giant Freshwater Prawns (Macrobrachium rosenbergii)

The giant freshwater prawn, Macrobrachium rosenbergii, is a prawn that has economic significance throughout the world. It exhibits sex-related growth dimorphism, whereby the males grow significantly more rapidly than the females. Therefore, a study on the molecular regulatory mechanism, which underlies the sexual differentiation of M. rosenbergii, is of both scientific and commercial importance. However, a scarcity of genomic and transcriptomic resources severely limits our knowledge of the sexual differentiation mechanisms in M. rosenbergii. Here, transcriptome sequencing of several gonadic samples of males and females in M. rosenbergii was performed to investigate the molecular basis underlying gonadal development. Our results showed that 2149 unigenes presented as differentially expressed genes (DEGs) in the ovaries of females compared to the testes of males, which contained 484 down-regulated and 1665 up-regulated genes. Enrichment analysis of DEGs revealed many of these genes to be related to sexual differentiation and gonadal development. From our transcriptome analyses, and as confirmed by quantitative real-time PCR, male-related genes (Mrr, MRPINK, IR, IAGBP, TESK1, and dsx) in the testes were significantly up-regulated, and female-related genes (ERR, Sxl3, cyclinB, Dmrt99B, PPP2A, and ADCY9) in the ovaries were also significantly up-regulated. This indicates the potential role these genes play in the gonadal development of M. rosenbergii. Furthermore, multiple signal transduction pathways relating to gonadal maturation and spermatogenesis, including MAPK, were identified herein. Our data also supports previous ideas that IAG and IAGBP-IR signaling schemes could help in the regulation of testis’ development in M. rosenbergii and the ERR gene could regulate ovarian development by affecting the expression of cyclinB, PPP2A, and ADCY9. The data from this study provides incredibly usefully genomic resources for future research on the sexual differentiation and practical aquaculture of M. rosenbergii.

Chemical synthesis and functional evaluation of the crayfish insulin-like androgenic gland factor

Insulin-like androgenic gland factor (IAG) from the marbled crayfish Procambarus virginalis is an insulin-like heterodimeric peptide composed of A and B chains and has an Asn-linked glycan at the B chain. IAG is considered to be a male sex hormone inducing the sex differentiation to male in decapod crustacean, although there is no report on the function of IAG peptide in vivo. In order to characterize P. virginalis IAG, we chemically synthesized it and evaluated its biological function in vivo. A and B chains were prepared by the ordinary solid-phase peptide synthesis, and three disulfide bonds were formed regioselectively by dimethyl sulfoxide oxidation, pyridylsulfenyl-directed thiolysis and iodine oxidation reactions. An IAG disulfide isomer was also prepared by the same manner. Circular dichroism spectral analysis revealed that the disulfide bond arrangement affected the peptide conformation, which was similar to the other insulin-family peptides analyzed so far. On the other hand, the glycan moiety attached at the B chain had no effect on the peptide secondary structure. Injection of the synthetic IAG and its disulfide isomer to female crayfish did not induce male characteristics on the external morphology, but both peptides suppressed the oocyte maturation in vivo. These results suggest that IAG has a pivotal role on the suppression of female secondary sex characteristics.

RNA Interference Analysis Reveals the Positive Regulatory Role of Ferritin in Testis Development in the Oriental River Prawn, Macrobrachium nipponense

Ferritin plays an essential role in organismic and cellular iron homeostasis in Macrobrachium nipponense. In this study, we aimed to investigate the role of ferritin in the sexual development of male M. nipponense. According to the qPCR analysis of different tissues and developmental stages, ferritin exhibited high expression levels in the testis and androgenic gland, from post-larval developmental stage 5 (PL5) to PL15, indicating that it may be involved in gonad differentiation and development, especially in male sexual development. In situ hybridization and qPCR analysis in various reproductive cycles of the testis indicated that ferritin may play an essential role in spermatogonia development in M. nipponense. RNAi analysis revealed that ferritin positively affected mRNA expression of the insulin-like androgenic gland (Mn-IAG) and the secretion of testosterone, and thus positively affected testis development in M. nipponense. This study highlighted the functions of ferritin in the sexual development of male M. nipponense and provided important information for the establishment of a technique to regulate the process of testis development in M. nipponense.

Identification of Important Genes Involved in the Sex-Differentiation Mechanism of Oriental River Prawn, Macrobrachium nipponense, During the Gonad Differentiation and Development Period

Identification of important genes, involved in the gonad differentiation and development, plays essential roles in the establishment of the artificial technique to regulate the process of testis development in M. nipponense. In this study, we aimed to determine the sensitive period of gonad differentiation and development through hematoxylin and eosin (HE) staining. The important genes involved in the gonad differentiation and development of M. nipponense were then identified through transcriptome profiling analysis during the sensitive period of gonad differentiation and development. HE staining analysis revealed that the sensitive period of gonad differentiation and development was from the post–larval developmental stages 5 (PL5) to PL25, which was dramatically faster than was for the other identified aquatic animals. The transcriptome profiling analysis predicted that phagosome, lysosome, oxidative phosphorylation, and glycolysis/gluconeogenesis play essential roles in the mechanism of gonad differentiation and development in M. nipponense. A total of 29 genes were further identified as the candidate genes, involved in the process of gonad differentiation and development in M. nipponense, based on the gene annotation and gene expression pattern. The qPCR analysis of Mn-JHEH, Mn-DHP, Mn-ALY, and Mn-SMA6 during the whole developmental process revealed that all of these four genes showed high expression levels during the sensitive period of gonad differentiation and development in M. nipponense. Mn-JHEH, Mn-DHP, and Mn-ALY showed higher expressions at PL25F than at PL25M, while Mn-SMA6 showed a higher expression at PL25M. The RNA interference (RNAi) analysis was further used to investigate the potential functions of SMA6 in male sexual development of M. nipponense. The RNAi analysis revealed that SMA6 positively regulated the testis development in M. nipponense by affecting the expression of Mn-IAG. This study provided valuable evidences for the establishment of the technique to regulate the process of gonad development in M. nipponense.

Seasonal changes in the expression of insulin-like androgenic hormone (IAG) in the androgenic gland of the Jonah crab, Cancer borealis

Harvesting the adult male Jonah crab, Cancer borealis, mainly based on the size, has become an economically significant fishery, particularly in the Southern New England region of the US since 2000. Many decapod crustacean fisheries including C. borealis rely on harvesting adult males. Understanding the size related-sexual maturity and the seasonal changes in male reproductive activity is critical for sustainable management. In other decapods, an insulin-like hormone produced by the male-specific androgenic gland (AG), called insulin-like androgenic gland factor (IAG), plays an essential role in sexual maturity. Specifically IAG is involved in developing male primary and secondary sexual characteristics including spermatogenesis. This study aimed first to identify the IAG, then examine if season influences IAG expression in C. borealis males. Finally, the AG transcriptome was used to test if eyestalk neuropeptides regulate IAG levels via an endocrine axis between the two endocrine tissues as established in other crustaceans. The full-length CabIAG sequence is 928 nucleotides long, encoding a 151 amino acid deduced sequence. The CabIAG identified from the AG transcriptome after eyestalk ablation was the most highly expressed gene and accounted for up to 25% of transcripts, further confirming the presence of an endocrine axis between the androgenic gland and eyestalk ganglia. This gene expression was exclusive in male C. borealis AG. The transcriptomic analysis also revealed strong upregulation of the PPOAE transcript and downregulation of proteolytic enzymes. The CabIAG levels differ by season, increasing AG activity in fall and possibly coinciding with high mating activity. The timing of increased AG activity correlating to mating with females should be considered for better stock management for the C. borealis population.

Genes Encoding the Glycoprotein Hormone GPA2/GPB5 and the Receptor LGR1 in a Female Prawn

In vertebrate reproduction, metabolism, growth and development, essential roles are played by glycoprotein hormones, such as follicle-stimulating hormone (FSH), luteinizing hormone (LH) and thyroid-stimulating hormone (TSH), all of which are heterodimers consisting of two subunits, a structurally identical alpha subunit, and a variable beta subunit, which provides specificity. A 'new' glycoprotein hormone heterodimer identified in both vertebrates and invertebrates, including decapod crustaceans, was shown to be composed of the glycoprotein alpha 2 (GPA2) and glycoprotein beta 5 (GPB5) subunits. The putative receptor for GPA2/GPB5 in invertebrates is the leucine-rich repeat-containing G protein-coupled receptor 1 (LGR1). In this study in the giant freshwater prawn, Macrobrachium rosenbergii, we identified and characterized the GPA2 (MrGPA2), GPB5 (MrGPB5) and LGR1 (MrLGR1) encoding genes and revealed their spatial expression patterns in female animals. Loss-of-function RNA interference (RNAi) experiments in M. rosenbergii females demonstrated a negative correlation between MrGPA2/MrGPB5 silencing and MrLGR1 transcript levels, suggesting a possible ligand-receptor interaction. The relative transcript levels of M. rosenbergii vitellogenin (MrVg) in the hepatopancreas were significantly reduced following MrGPA2/MrGPB5 knockdown. MrLGR1 loss-of-function induced MrVg receptor (MrVgR) transcript levels in the ovary and resulted in significantly larger oocytes in the silenced group compared to the control group. Our results provide insight into the possible role of GPA2/GPB5-LGR1 in female reproduction, as shown by its effect on MrVg and MrVgR expression and on the oocyte development. Here, we suggest that the GPA2/GPB5 heterodimer act as a gonad inhibiting factor in the eyestalk-hepatopancreas-ovary endocrine axis in M. rosenbergii.

Identification and expression pattern of the sex determination gene fruitless-like in Cherax quadricarinatus

The fruitless (fru) gene has an important function in the courtship behavior and sex determination pathway of Drosophila melanogaster; however, the fru gene has never been reported in shrimps. In this study, the fruitless-like gene was identified in Cherax quadricarinatus (Cqfru) and is reported here for the first time. A sequence analysis revealed a conserved BTB domain in Cqfru which is the same as fru in D. melanogaster. An analysis of the expression level of Cqfru showed that it was highly expressed in the gastrula stage during embryonic development. Furthermore, in situ hybridization and expression distribution in tissues showed that its sexually dimorphic expression may be focused on the hepatopancreas, brains, and gonads. The gonads, brains, and hepatopancreas of males had a higher expression level of Cqfru than those of females; however, the expression level of the abdominal ganglion was found to be higher in females than in males in this study. The results of an RNA interference treatment showed that a knockdown of Cqfru reduced the expression of the insulin-like androgenic gland hormone (IAG) and tumor necrosis factor (TNF). The characteristic fru gene in shrimps is reported here for the first time, with the results providing basic information for research into the sex-determination mechanism in C. quadricarinatus.

Identification and Characterization of the Pyruvate Dehydrogenase E1 Gene in the Oriental River Prawn, Macrobrachium nipponense

Pyruvate dehydrogenase E1 (PDHE1) is thought to play essential roles in energy metabolism, and a previous study suggested that it also has potential regulatory roles in male sexual development in the oriental river prawn, Macrobrachium nipponense. In this study, we used rapid amplification of cDNA ends, quantitative polymerase chain reaction (qPCR), in situ hybridization, western blotting, RNA interference (RNAi), and histological analyses to assess the potential functions of Mn-PDHE1 in the sexual development of male M. nipponense. The full cDNA sequence of Mn-PDHE1 was 1,614 base pairs long, including a 1,077 base pair open reading frame that encodes 358 amino acids. qPCR analysis revealed the regulatory functions of PDHE1 in male sexual development in M. nipponense and in the metamorphosis process. In situ hybridization and western blot results indicated that PDHE1 was involved in testis development, and RNAi analysis showed that PDHE1 positively regulated the expression of insulin-like androgenic gland factor in M. nipponense. Compared with the cell types in the testes of control prawns, histological analysis showed that the number of sperm was dramatically lower after test subjects were injected with Mn-PDHE1 dsRNA, whereas the numbers of spermatogonia and spermatocytes were higher. Sperm constituted only 1% of cells at 14 days after injection in the RNAi group. This indicated that knockdown of the expression of PDHE1 delayed testis development. Thus, PDHE1 has positive effects on male sexual development in M. nipponense. This study highlights the functions of PDHE1 in M. nipponense and its essential roles in the regulation of testis development.

Identification of candidate genes from androgenic gland in Macrobrachium nipponense regulated by eyestalk ablation

The eyestalk of crustaceans, such as Macrobrachium nipponense, contains many neurosecretory hormones affecting the process of reproduction, molting, metabolism of glucose, and other functions. In this study, important metabolic pathways and candidate genes involved in male sexual development were selected from M. nipponense. The methodology involved performing long-read and next generation transcriptome sequencing of genes from the androgenic gland after eyestalk ablation. qPCR analysis revealed that the mRNA expression of Mn-IAG was significantly increased after ablation of both the single-side (SS) and double-side (DS) eyestalk, compared with the control group (CG). The long-read transcriptome generated 49,840 non-redundant transcripts. A total of 1319, 2092 and 4351 differentially expressed genes (DEGs) were identified between CG versus SS, SS versus DS and CG versus DS, respectively. These data indicated that ablation of the double-sided eyestalk played stronger regulatory roles than the single-side ablation on male sexual development in M. nipponense. This was consistent with the qPCR analysis. Cell Cycle, Cellular Senescence, Oxidative Phosphorylation, Glycolysis/Gluconeogenesis and Steroid Hormone Biosynthesis were the primary enriched metabolic pathways in all three comparisons, and the important genes from these metabolic pathways were also selected. qPCR permitted secondary confirmation of ten DEGs identified through RNA-seq. RNAi-mediated silencing analyses of Hydroxysteroid dehydrogenase like 1 (HSDL1) revealed that HSDL1 has a positive regulatory effect on testes development. This study provides valuable insight into male sexual development in M. nipponense, including metabolic pathways and genes, paving the way for advanced studies on male sexual development in this species and in other crustaceans.

Feminising Wolbachia disrupt Armadillidium vulgare insulin-like signalling pathway

The endosymbiont Wolbachia feminises male isopods by making them refractory to the insulin-like masculinising hormone, which shunts the autocrine development of the androgenic glands. It was, therefore, proposed that Wolbachia silences the IR receptors, either by preventing their expression or by inactivating them. We describe here the two IR paralogs of Armadillidium vulgare. They displayed a conventional structure and belonged to a family widespread among isopods. Av-IR1 displayed an ubiquist expression, whereas the expression of Av-IR2 was restricted to the gonads. Both were constitutively expressed in males and females and throughout development. However, upon silencing, altered gland physiology and gene expression therein suggested antagonistic roles for Av-IR1 (androinhibiting) and Av-IR2 (androstimulating). They may function in tandem with regulating neurohormones, as a conditional platform that conveys insulin signalling. Wolbachia infection did not alter their expression patterns: leaving the IRs unscathed, the bacteria would suppress the secretion of the neurohormones, thus inducing body-wide IR deactivation and feminisation. Adult males injected with Wolbachia acquired an intersexed physiology. Their phenotypes and gene expressions mirrored the silencing of Av-IR1 only, suggesting that imperfect feminisation stems from a flawed invasion of the androstimulating centre, whereas in fully feminised males invasion would be complete in early juveniles. TAKE AWAY: Two antagonistic Insulin Receptors were characterised in Armadillidium vulgare. The IRs were involved in androstimulating and androinhibiting functions. Wolbachia-induced feminisation did not prevent the expression of the IRs. Imperfectly feminised intersexes phenocopied the silencing of Av-IR1 only. Wolbachia would deactivate the IRs by suppressing neurosecretory co-factors.

Identification and Characterization of the Succinate Dehydrogenase Complex Iron Sulfur Subunit B Gene in the Oriental River Prawn, Macrobrachium nipponense

Previous studies have revealed that SDHB has potential functions in the male sexual differentiation and development in M. nipponense through providing ATP. In this study, the functions of Mn-SDHB were further analyzed in depth using quantitative polymerase chain reaction (qPCR), in situ hybridization, western-blot, and RNA interference (RNAi), combined with the histological observations. The full-genome sequence of Mn-SDHB was 54,608 bp at Chromosome 34, including 7 introns and 6 exons. The full-length cDNA sequence of Mn-SDHB was 1,268 base pairs (bp) long with an open reading frame of 807 bp, encoding for 268 amino acids. The highest expression level of Mn-SDHB in different tissues was observed in the testis, and male prawns at post-larval developmental stage 25 during different developmental stages, indicating that SDHB was potentially involved in the male sexual development in M. nipponense. In situ hybridization and western-blot analysis indicated that SDHB plays essential roles in the testis development. The in situ hybridization analysis also implies the potential roles of Mn-SDHB in ovarian development. The expressions of Mn-IAG were decreased after Mn-SDHB dsRNA injection, indicating SDHB has the positive regulatory effects on IAG in M. nipponese. Thus, SDHB was involved in the mechanism of the male sexual development. The testis development was inhibited, and sperms were rarely observed after 10 days of Mn-SDHB dsRNA injection, indicating SDHB has positive effects on the male sexual development in M. nipponense. This study highlights the functions of SDHB in M. nipponense, which provide new insights for the future studies of the male sexual development in other crustacean species.

Genes encoding putative bicarbonate transporters as a missing molecular link between molt and mineralization in crustaceans

During their life, crustaceans undergo several molts, which if theoretically compared to the human body would be equivalent to replacing all bones at a single event. Such a dramatic repetitive event is coupled to unique molecular mechanisms of mineralization so far mostly unknown. Unlike human bone mineralized with calcium phosphate, the crustacean exoskeleton is mineralized mainly by calcium carbonate. Crustacean growth thus necessitates well-timed mobilization of bicarbonate to specific extracellular sites of biomineralization at distinct molt cycle stages. Here, by looking at the crayfish Cherax quadricarinatus at different molting stages, we suggest that the mechanisms of bicarbonate ion transport for mineralization in crustaceans involve the SLC4 family of transporters and that these proteins play a key role in the tight coupling between molt cycle events and mineral deposition. This discovery of putative bicarbonate transporters in a pancrustacean with functional genomic evidence from genes encoding the SLC4 family-mostly known for their role in pH control-is discussed in the context of the evolution of calcium carbonate biomineralization.

Transcriptome Profiling Analysis of the Testis After Eyestalk Ablation for Selection of the Candidate Genes Involved in the Male Sexual Development in Macrobrachium nipponense

The eyestalk of crustacean species secretes many hormones, affecting the process of reproduction, molting, metabolism of glucose, and other functions in crustaceans. In this study, important metabolic pathways and candidate genes involved in the male sexual development were identified through performing the transcriptome profiling analysis of the testis after the ablation of eyestalk from Macrobrachium nipponense. The histological observations revealed that the testis development became vigorous after eyestalk ablation, indicating that the hormones secreted by the eyestalk have negative effects on the testis development in M. nipponense. Transcriptome profiling analysis revealed that 1,039, 1,226, and 3,682 differentially expressed genes (DEGs) were identified between normal prawns (CG) vs single-side eyestalk ablation prawns (SS), SS vs double-side eyestalk ablation prawns (DS), and CG vs DS, respectively, indicating that the ablation of double-side eyestalk has more significant regulatory roles on male sexual development than that of single-side ablation, which was consistent with the histological observations. Lysosome, Apoptosis, Glycolysis/Gluconeogenesis, and Insulin signaling pathway were the main enriched metabolic pathways in all of these three comparisons, and the important genes from these metabolic pathways were also selected. The qPCR verifications of 10 DEGs from these metabolic pathways were the same as those of RNA-seq. The qPCR, in situ hybridization, and RNA interference analysis of Mn-NF_kBα revealed that NF_kBα has a positive regulatory effect on testis development. This study provided new insights on male sexual development in M. nipponense, promoting the studies on male sexual development in other crustaceans as well.

RNA Interference in Aquaculture: A Small Tool for Big Potential

For decades, the tight regulatory functions of DNA and RNA have been the focus of extensive research with the goal of harnessing RNA molecules (e.g., microRNA and small interfering RNA) to control gene expression and to study biological functions. RNA interference (RNAi) has shown evidence of mediating gene expression, has been utilized to study functional genomics, and recently has potential in therapeutic agents. RNAi is a natural mechanism and a well-studied tool that can be used to silence specific genes. This method is also used in aquaculture as a research tool and to enhance immune responses. RNAi methods do have their limitations (e.g., immune triggering); efficient and easy-to-use RNAi methods for large-scale applications need further development. Despite these limitations, RNAi methods have been successfully used in aquaculture, in particular shrimp. This review discusses the uses of RNAi in aquaculture, such as immune- and production-related issues and the possible limitations that may hinder the application of RNAi in the aquaculture industry. Our challenge is to develop a highly potent in vivo RNAi delivery platform that could complete the desired action with minimal side effects and which can be applied on a large-scale with relatively little expense in the aquaculture industry.

Identification and characterization of sex-biased and differentially expressed miRNAs in gonadal developments of the Chinese mitten crab, Eriocheir sinensis

MicroRNA (miRNA) is a posttranscriptional downregulator that plays a vital role in a wide variety of biological processes. In this study, we constructed five ovarian and testicular small RNA libraries using two somatic libraries as reference controls for the identification of sex-biased miRNAs and gonadal differentially expressed miRNAs (DEMs) of the Chinese mitten crab, Eriocheir sinensis. A total of 535 known and 243 novel miRNAs were identified, including 312 sex-biased miRNAs and 402 gonadal DEMs. KEGG pathway analysis showed that DEM target genes were statistically enriched in MAPK, Wnt, and GnRH signaling pathway, and so on. A number of the sex-biased miRNAs target genes associated with sex determination/differentiation, such as IAG, Dsx, Dmrt1, and Fem1, while others target the genes related to gonadal development, such as P450s, Wnt, Ef1, and Tra-2c. Dual-luciferase reporter assay in vitro further confirmed that miR-34 and let-7b can downregulate IAG expression, miR-9-5p, let-7d, let-7b, and miR-8915 can downregulate Dsx. Taken together, these data strongly suggest a potential role for the sex-biased miRNAs in sex determination/differentiation and gonadal development in the crab.

Insulin-like androgenic gland hormone 1 (IAG1) regulates sexual differentiation in a hermaphrodite shrimp through feedback to neuroendocrine factors

Insulin-like androgenic gland hormone (IAG) is regarded as a key sexual differentiation regulator in gonochoristic crustaceans. However, until now the knowledge concerning its functions in hermaphroditic crustaceans is scanty. Herein, we investigated the function of IAG (Lvit-IAG1) in peppermint shrimp Lysmata vittata, a species that possesses protandric simultaneous hermaphroditism (PSH) reproductive system, which is rare among crustaceans. Lvit-IAG1 was exclusively expressed in the androgenic gland. The qRT-PCR demonstrated that its mRNA expression level was relatively high at the functional male phase but decreased sharply in the subsequent euhermaphrodite phase. Both the short-term and long-term silencing experiments showed that Lvit-IAG1 negatively regulated both the gonad-inhibiting hormone (Lvit-GIH) and crustacean female sex hormone (Lvit-CFSH) expressions in the eyestalk ganglion. Besides, Lvit-IAG1 gene knockdown induced a retarded development of the appendices masculinae (AM) and male gonopores while suppressing the germ cells at the primary spermatocyte stage. Also, Lvit-IAG1 gene silencing hindered ovarian development. This in turn led to small vitellogenic oocytes and decreased expression of vitellogenin and vitellogenin receptor genes in hepatopancreas and ovarian region, respectively. Generally, this study's findings imply that Lvit-IAG1 modulated the male sexual differentiation in PSH species L. vittata, and exhibited negative feedback on Lvit-GIH and Lvit-CFSH genes expression in the species' eyestalk ganglion.

Sex Determination and Differentiation in Decapod and Cladoceran Crustaceans: An Overview of Endocrine Regulation

Mechanisms underlying sex determination and differentiation in animals are known to encompass a diverse array of molecular clues. Recent innovations in high-throughput sequencing and mass spectrometry technologies have been widely applied in non-model organisms without reference genomes. Crustaceans are no exception. They are particularly diverse among the Arthropoda and contain a wide variety of commercially important fishery species such as shrimps, lobsters and crabs (Order Decapoda), and keystone species of aquatic ecosystems such as water fleas (Order Branchiopoda). In terms of decapod sex determination and differentiation, previous approaches have attempted to elucidate their molecular components, to establish mono-sex breeding technology. Here, we overview reports describing the physiological functions of sex hormones regulating masculinization and feminization, and gene discovery by transcriptomics in decapod species. Moreover, this review summarizes the recent progresses of studies on the juvenile hormone-driven sex determination system of the branchiopod genus Daphnia, and then compares sex determination and endocrine systems between decapods and branchiopods. This review provides not only substantial insights for aquaculture research, but also the opportunity to re-organize the current and future trends of this field.

A chromosome-level genome assembly of the oriental river prawn, Macrobrachium nipponense

BACKGROUND

The oriental river prawn, Macrobrachium nipponense, is an economically important shrimp in China. Male prawns have higher commercial value than females because the former grow faster and reach larger sizes. It is therefore important to reveal sex-differentiation and development mechanisms of the oriental river prawn to enable genetic improvement.

RESULTS

We sequenced 293.3 Gb of raw Illumina short reads and 405.7 Gb of Pacific Biosciences long reads. The final whole-genome assembly of the Oriental river prawn was ∼4.5 Gb in size, with predictions of 44,086 protein-coding genes. A total of 49 chromosomes were determined, with an anchor ratio of 94.7% and a scaffold N50 of 86.8 Mb. A whole-genome duplication event was deduced to have happened 109.8 million years ago. By integration of genome and transcriptome data, 21 genes were predicted as sex-related candidate genes.

CONCLUSION

The first high-quality chromosome-level genome assembly of the oriental river prawn was obtained. These genomic data, along with transcriptome sequences, are essential for understanding sex-differentiation and development mechanisms in the oriental river prawn, as well as providing genetic resources for in-depth studies on developmental and evolutionary biology in arthropods.

A Crab Is Not a Fish: Unique Aspects of the Crustacean Endocrine System and Considerations for Endocrine Toxicology

Crustaceans-and arthropods in general-exhibit many unique aspects to their physiology. These include the requirement to moult (ecdysis) in order to grow and reproduce, the ability to change color, and multiple strategies for sexual differentiation. Accordingly, the endocrine regulation of these processes involves hormones, receptors, and enzymes that differ from those utilized by vertebrates and other non-arthropod invertebrates. As a result, environmental chemicals known to disrupt endocrine processes in vertebrates are often not endocrine disruptors in crustaceans; while, chemicals that disrupt endocrine processes in crustaceans are often not endocrine disruptors in vertebrates. In this review, we present an overview of the evolution of the endocrine system of crustaceans, highlight endocrine endpoints known to be a target of disruption by chemicals, and identify other components of endocrine signaling that may prove to be targets of disruption. This review highlights that crustaceans need to be evaluated for endocrine disruption with consideration of their unique endocrine system and not with consideration of the endocrine system of vertebrates.

Full Functional Sex Reversal Achieved Through Silencing of MroDmrt11E Gene in Macrobrachium rosenbergii: Production of All-Male Monosex Freshwater Prawn

The freshwater prawn Macrobrachium rosenbergii is one kind of important economic aquaculture species and displays remarkable sexual dimorphism. The molecular mechanism of sexual differentiation in M. rosenbergii has been primarily unraveled through the research efforts of the androgenic gland and its related genes. However, the understanding of conserved genes involved in the molecular mechanism underpinning sex determination and sexual differentiation of M. rosenbergii is still fragmentary. MroDmrt11E is a member of the doublesex and mab-3-related transcription factor (Dmrt) gene family and is prominently expressed in the testis. In the present study, in vivo knockdown of MroDmrt11E at the postlarva stage in male prawn induced a complete and functional sex reversal and achieved the production of an all-male monosex population. Furthermore, a great deal of new information of upregulated and downregulated transcriptions involved in sexual differentiation of MroDmrt11E knockdown was enriched by comparative transcriptomic analysis. The effects of RNAi-mediated gene knockdown of MroDmrt11E on the differentially expressed and sex-related candidate genes, such as transformer, fruitless, feminization, insulin-like androgenic gland gene, Dmrt gene family, were primarily focused on, and their possible molecular regulatory relationships in sexual differentiation were analyzed. Meanwhile, the response of primary Kyoto Encyclopedia of Genes and Genomes (KEGG) biological pathways was investigated to expound the potential roles of MroDmrt11E in male sexual differentiation, which provided a deeper understanding of the molecular regulatory network underlying sexual differentiation of M. rosenbergii. The finding provided a novel sexual manipulation technique through silencing of Dmrt gene family for achieving a complete and functional sex reversal and offered a new insight regarding the mechanism of the Dmrt gene family in the sexual differentiation of crustaceans.

Multi-Tissue Transcriptome Analysis Identifies Key Sexual Development-Related Genes of the Ornate Spiny Lobster (Panulirus ornatus)

Sexual development involves the successive and overlapping processes of sex determination, sexual differentiation, and ultimately sexual maturation, enabling animals to reproduce. This provides a mechanism for enriched genetic variation which enables populations to withstand ever-changing environments, selecting for adapted individuals and driving speciation. The molecular mechanisms of sexual development display a bewildering diversity, even in closely related taxa. Many sex determination mechanisms across animals include the key family of "doublesex- and male abnormal3-related transcription factors" (Dmrts). In a few exceptional species, a single Dmrt residing on a sex chromosome acts as the master sex regulator. In this study, we provide compelling evidence for this model of sex determination in the ornate spiny lobster Panulius ornatus, concurrent with recent reports in the eastern spiny lobster Sagmariasus verreauxi. Using a multi-tissue transcriptomic database established for P. ornatus, we screened for the key factors associated with sexual development (by homology search and using previous knowledge of these factors from related species), providing an in-depth understanding of sexual development in decapods. Further research has the potential to close significant gaps in our understanding of reproductive development in this ecologically and commercially significant order.