The gene encoding the insulin-like androgenic gland hormone in an all-female parthenogenetic crayfish

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.

New insights for the regulatory feedback loop between type 1 crustacean female sex hormone (CFSH-1) and insulin-like androgenic gland hormone (IAG) in the Chinese mitten crab (Eriocheir sinensis)

To clarify the hormone control on sex determination and differentiation, we studied the Chinese mitten crab, Eriocheir sinensis (Henri Milne Edwards, 1854), a species with importantly economic and ecological significance. The crustacean female sex hormone (CFSH) and the insulin-like androgenic gland hormone (IAG) have been found to be related to the sex determination and/or differentiation. CFSH-1 of E. sinensis (EsCFSH-1) encoded a 227 amino-acid protein including a signal peptide, a CFSH-precursor-related peptide, and a mature CFSH peptide. Normally, EsCFSH-1 was highly expressed in the eyestalk ganglion of adult female crabs, while the expression was declined in the intersex crabs (genetic females). The intersex crabs had the androgenic glands, and the expression level of EsIAG was close to that of male crabs. During the embryogenesis and larval development, the changes of EsCFSH-1 and EsIAG genes expression in male and female individuals were shown after the zoea IV stage. Next, we confirmed the existence of the regulatory feedback loop between EsCFSH-1 and EsIAG by RNA interference experiment. The feminization function of EsCFSH-1 was further verified by examining the morphological change of external reproductive organs after EsCFSH-1 knockdown. The findings of this study reveal that the regulatory interplay between CFSH and IAG might play a pivotal role in the process of sex determination and/or differentiation in decapod crustaceans.

Two Short Repeats in the 5′ Untranslated Region of Insulin-like Androgenic Gland Factor in Procambarus clarkii (PcIAG) That Regulate PcIAG Expression

Insulin-like androgenic gland factor (IAG) plays an important role in sex manipulation in decapods. Understanding the molecular regulation mechanism of IAG in Procambarus clarkii (PcIAG) is important for realizing its sex control. In this study, the promoter and gene structure of PcIAG, mRNA, and miRNA expression profiles after interfering with two siRNAs synthesized according to the two short repeats in the 5′ untranslated regions (5′UTR) of PcIAG were analyzed, and miRNAs of exosomes were investigated to explore the role of repeated sequences with tandem two short repeats located in the 5′UTR of PcIAG isolated from the androgenic gland (AG) in the regulation of IAG expression. The results showed that the repeated sequences of 5′UTR only occurred completely in the cDNA from AG, and the function of the two repeats was different in regulating the expression of PcIAG, in which the Wnt signaling pathway may be involved. Furthermore, we found that six miRNAs including miR-133, miR-193, miR-34, miR-1, miR-100, and let-7 might be involved in the regulation of the expression of PcIAG, wherein miR-133 might directly be related with the repeated sequences of 5′UTR.

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.

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.

Cloning, functional and regulation analysis of a novel male reproduction-related protein gene from the oriental river prawn Macrobrachium nipponense

Gonadogenesis processes in crustaceans are complex. There, however, has been a large amount of research focused on regulation of female gonad (ovary) development in crustaceans, however, there has been little focus on the male gonad (testis). In the current study, a novel male reproduction-related protein gene (Mn-MRP) was identified from Macrobrachium nipponense. The relative abundance of Mn-MRP mRNA transcript in tissues and at different developmental stages were investigated. The relative abundance of Mn-MRP mRNA transcript was larger in the testis than other tissues, and during the testis maturation stage than at other developmental stages, suggesting Mn-MRP may have important functions in reproduction processes. The RNA interference (RNAi) was used to further investigate the Mn-MRP biological function. Silencing of the Mn-MRP gene effectively decreased the abundance of the sperm gelatinase (Mn-SG) mRNA transcript, implying the protein encoded by this gene may have functions in sperm activity during the fertilization process. Further studies with RNAi and eyestalk ablation confirmed that gonad inhibiting hormone gene (Mn-GIH) is a negative regulator of Mn-MRP, and that the insulin-like androgenic gland hormone gene (Mn-IAG) is a positive regulator. There, therefore, was cloning of the Mn-MRP gene, and investigation of its potential biological function, as well as elucidation of the positive/negative regulators in current study. The results from this study provide for a greater understanding of regulatory mechanisms of male reproduction in crustaceans.

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.

Insulin-like androgenic gland hormone from the shrimp Fenneropenaeus merguiensis: Expression, gene organization and transcript variants

Male sex differentiation in the crustacean is best known to be controlled by the insulin-like androgenic gland hormone (IAG). In this report, the cDNA and gene of the shrimp Fenneropenaeus merguiensis FmIAG were studied and characterized. FmIAG gene shares a high sequence identity in the coding region as well as the promoter region with that of F. chinensis. FmIAG gene is most likely consists of 5 exons and 4 introns. The cDNA reported here is the most abundant transcript that retained cryptic intron 4. The use of different splicing acceptor sites in exon 2 can produce a long-form FmIAG transcript variant with 6 additional amino acids inserted. Splicing of cryptic intron 4 would produce a transcript variant with a different C-terminal end. Therefore 4 different FmIAG transcripts can be produced from the FmIAG gene. During the molt cycle, the expression level of FmIAG was low in the early intermolt, increase steadily towards the late premolt and decreased rapidly in the early postmolt. In addition to the androgenic gland, FmIAG is also expressed in the hepatopancreas and ovary of adult females. Unilateral eyestalk ablation caused a significant increase in FmIAG transcript suggesting that the eyestalk consists of inhibiting factor(s) that suppressesFmIAGexpression. To explore the function of FmIAG in males, injection of FmIAG dsRNA knock-down the expression of FmIAG and up-regulated the expression of the vitellogenin gene in the testis and hepatopancreas. Interestingly a CHH-like gene identified in the androgenic gland was down-regulated. CHH-like gene knock-down resulted in altered expression of FmIAG in males suggesting that the CHH-like may be involved in FmIAG's regulation. RT-PCR with specific primers to the different transcript variant were used to determine if there is an association of different sizes of male and the type of IAG transcript. Results indicated that a high percentage of the large male shrimp expressed the long-form of FmIAG. The results suggested that FmIAG may be useful as a size marker for male shrimp aquaculture. In summary, the results of this study have expanded our knowledge of shrimp insulin-like androgenic gland hormone in male sex development and its potential role as a marker gene for growth regulation in shrimp.

Gonadulins, the fourth type of insulin-related peptides in decapods

Insulin and related peptides play important roles in the regulation of growth and reproduction. Until recently three different types of insulin-related peptides had been identified from decapod crustaceans. The identification of two novel insulin-related peptides from Sagmariasus verreauxi and Cherax quadricarinatus suggested that there might a fourth type. Publicly available short read archives show that orthologs of these peptides are commonly present in these animals. Most decapods have two genes coding such peptides, but Penaeus species have likely only one and some palaemonids have three. Interestingly, expression levels can vary more than thousand-fold in the gonads of Portunus trituberculatus, where gonadulin 1 is expressed by the testis and gonadulin 2 by the ovary. Although these peptides are also expressed in other tissues, the occasionally very high expression in the gonads led to them being called gonadulins.

The "IAG-Switch"-A Key Controlling Element in Decapod Crustacean Sex Differentiation

The androgenic gland (AG)-a unique crustacean endocrine organ that secretes factors such as the insulin-like androgenic gland (IAG) hormone-is a key player in crustacean sex differentiation processes. IAG expression induces masculinization, while the absence of the AG or a deficiency in IAG expression results in feminization. Therefore, by virtue of its universal role as a master regulator of crustacean sexual development, the IAG hormone may be regarded as the sexual "IAG-switch." The switch functions within an endocrine axis governed by neuropeptides secreted from the eyestalks, and interacts downstream with specific insulin receptors at its target organs. In recent years, IAG hormones have been found-and sequenced-in dozens of decapod crustacean species, including crabs, prawns, crayfish and shrimps, bearing different types of reproductive strategies-from gonochorism, through hermaphroditism and intersexuality, to parthenogenesis. The IAG-switch has thus been the focus of efforts to manipulate sex developmental processes in crustaceans. Most sex manipulations were performed using AG ablation or knock-down of the IAG gene in males in order to sex reverse them into "neo-females," or using AG implantation/injecting AG extracts or cells into females to produce "neo-males." These manipulations have highlighted the striking crustacean sexual plasticity in different species and have permitted the manifestation of either maleness or femaleness without altering the genotype of the animals. Furthermore, these sex manipulations have not only facilitated fundamental studies of crustacean sexual mechanisms, but have also enabled the development of the first IAG-switch-based monosex population biotechnologies, primarily for aquaculture but also for pest control. Here, we review the crustacean IAG-switch, a unique crustacean endocrine mechanism, from the early discoveries of the AG and the IAG hormone to recent IAG-switch-based manipulations. Moreover, we discuss this unique early pancrustacean insulin-based sexual differentiation control mechanism in contrast to the extensively studied mechanisms in vertebrates, which are based on sex steroids.

The protandric life history of the Northern spot shrimp Pandalus platyceros: molecular insights and implications for fishery management

The Northern spot shrimp, Pandalus platyceros, a protandric hermaphrodite of commercial importance in North America, is the primary target species for shrimp fisheries within Southeast Alaska. Fishery data obtained from the Alaska Department of Fish and Game indicate that spot shrimp populations have been declining significantly over the past 25 years. We collected spot shrimps in Southeast Alaska and measured reproductive-related morphological, gonadal and molecular changes during the entire life history. The appendix masculina, a major sexual morphological indicator, is indicative of the reproductive phase of the animal, lengthening during maturation from juvenile to the male phase and then gradually shortening throughout the transitional stages until its complete disappearance upon transformation to a female. This morphological change occurs in parallel with the degeneration of testicular tissue in the ovotestis and enhanced ovarian vitellogenesis. Moreover, we obtained the entire mRNA sequence of the yolk protein precursor, vitellogenin, and monitored its transcript levels throughout the entire shrimp life-cycle. Vitellogenin transcript levels in the hepatopancreas increased in the early transitional stage until reaching a peak prior to extruding eggs. Such transcriptomic analyses, coupled with a comprehensive description of the gonad, external sex characters and timing of the reproductive life history of spot shrimps contribute to a better understanding of the hermaphroditic reproduction process in the cold Southeast Alaskan waters. This knowledge can contribute to a revision of current conservation efforts to maintain wild populations sustainable for both commercial and ecological considerations.

Molecular Characterization and Functional Study of Insulin-Like Androgenic Gland Hormone Gene in the Red Swamp Crayfish, Procambarus clarkii

The androgenic gland (AG) is a male-specific endocrine organ that controls the primary and secondary sexual characteristics in male crustaceans. More evidence indicates that the insulin-like androgenic gland hormone gene (IAG) is the key male sexual differentiation factor, particularly the application of RNA interference (RNAi) technology on IAG. In this study, the full-length cDNA of IAG (termed PcIAG) was isolated from the red swamp crayfish, Procambarusclarkii. Tissue distribution analysis showed that in addition to its expression in the AG of male P. clarkii, PcIAG was widely expressed in female tissues and other male tissues. The PcIAG protein was detected in the reproductive and nervous systems of adult male P. clarkii. Additionally, RNAi results showed that the PcIAG expression could be silenced efficiently, and the male sperm maturation and release possibly present a transient adverse interference at lower doses (0.1 μg/g and 1 μg/g) of PcIAG–dsRNA (PcIAG double-stranded RNA). Dramatically, the expression level of PcIAG increased sharply shortly after the injection of higher doses (5 μg/g and 10 μg/g) of PcIAG–dsRNA, which might accelerate the maturation and release of sperm. Moreover, the expression of PcSxl (P. clarkii Sex-lethal) was detected by Quantitative Real-Time PCR (qPCR) after the injection of PcIAG–dsRNA to explore whether the PcIAG gene regulates the PcSxl gene, and we found that the PcIAG did not directly regulate PcSxl in P. clarkii. The study could help accelerate the progress of PcIAG functional research and provide a useful reference for the single-sex selective breeding of P. clarkii.

Investigating the genetic and epigenetic basis of big biological questions with the parthenogenetic marbled crayfish: A review and perspectives

In the last 15 years, considerable attempts have been undertaken to develop the obligately parthenogenetic marbled crayfish Procambarus virginalis as a new model in biology. Its main advantage is the production of large numbers of offspring that are genetically identical to the mother, making this crustacean particularly suitable for research in epigenetics. Now, a draft genome, transcriptome and genome-wide methylome are available opening new windows for research. In this article, I summarize the biological advantages and genomic and epigenetic features of marbled crayfish and, based on first promising data, discuss what this new model could contribute to answering of ''big'' biological questions. Genome mining is expected to reveal new insights into the genetic specificities of decapod crustaceans, the genetic basis of arthropod reproduction, moulting and immunity, and more general topics such as the genetic underpinning of adaptation to fresh water, omnivory, biomineralization, sexual system change, behavioural variation, clonal genome evolution, and resistance to cancer. Epigenetic investigations with the marbled crayfish can help clarifying the role of epigenetic mechanisms in gene regulation, tissue specification, adult stem cell regulation, cell ageing, organ regeneration and disease susceptibility. Marbled crayfish is further suitable to elucidate the relationship between genetic and epigenetic variation, the transgenerational inheritance of epigenetic signatures and the contribution of epigenetic phenotype variation to the establishment of social hierarchies, environmental adaptation and speciation. These issues can be tackled by experiments with highly standardized laboratory lineages, comparison of differently adapted wild populations and the generation of genetically and epigenetically edited strains.