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.

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.

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.

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.

RNAi Analysis of Potential Functions of Cyclin B3 in Reproduction of Male Oriental River Prawns (Macrobrachium nipponense)

Cyclin B3 (CycB3) is involved in the metabolic pathway of the cell cycle, playing essential roles in the regulation of cell proliferation and mitosis. CycB3 is also predicted to be involved in the reproduction of male oriental river prawns (Macrobrachium nipponense). In this study, the potential functions of CycB3 in M. nipponense were investigated using quantitative real-time PCR, RNA interference, and histological observations. The full-length DNA sequence of CycB3 in M. nipponense was 2147 base pairs (bp) long. An open reading frame of 1500 bp was found, encoding 499 amino acids. A highly conserved destruction box and two conserved cyclin motifs were found in the protein sequence of Mn-CycB3. Phylogenetic tree analysis revealed that this protein sequence was evolutionarily close to that of CycB3s of crustacean species. Quantitative real-time PCR analysis results suggested that CycB3 was involved in the process of spermiogenesis, oogenesis, and embryogenesis in M. nipponense. RNA interference analysis showed that CycB3 had a positive regulatory relationship with insulin-like androgenic gland hormone (IAG) in M. nipponense. In addition, sperm were rarely observed in the testis of double-stranded CycB3-injected prawns after 14 days of treatment, and sperm abundance was dramatically lower than that in the double-stranded GFP-injected prawns on the same day. This result indicated that CycB3 can regulate the testis reproduction in M. nipponense through inhibiting the IAG expressions. Overall, these results indicated that CycB3 plays essential roles in the regulation of male reproduction in M. nipponense, which may promote the studies of male reproduction in other crustacean species.

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.

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.

Comparison of effects of dsRNA and siRNA RNA interference on insulin-like androgenic gland gene (IAG) in red swamp crayfish Procambarus clarkii

RNA interference (RNAi), which employs double-strand RNA (dsRNA) or small interference RNA (siRNA), is a popular reverse genetic manipulation tool to study gene function. Presently, there is few reports on the implementation of RNAi on the insulin-like androgenic gland gene (IAG) in red swamp crayfish Procambarus clarkii. In this study, the effective sequence of siRNA and optimal injection dose were determined, and the effects of RNAi using dsRNA, siRNA, and long-term RNAi were investigated. The results showed that the doses of 0.5 and 1 µg/g of body weight of IAG-siRNA3 produced significantly better inhibition than 0.1 µg/g. qPCR assays showed that both dsRNA and siRNA silenced the IAG expression in five tissues (brain, ventral nerve cord, androgenic gland, testis, and vas deferens) in adult P. clarkii, with the effectiveness decreasing over time, inhibiting the production of spermatid. dsRNA exhibited a longer interference effect than siRNA in adults. For long-term interference (P. clarkii juveniles were injected 7 times with 1 µg/g of body weight of IAG-dsRNA), and found that the secondary sexual characteristics of juveniles were affected, while the control group developed normally. The results of this study could lay the foundation for crayfish sex reversal with IAG RNAi, and provide the reference for those studies in which the technique of RNAi was used.

Sex-Biased CHHs and Their Putative Receptor Regulate the Expression of IAG Gene in the Shrimp Litopenaeus vannamei

The “eyestalk-androgenic gland (AG)-testis” endocrine axis is involved in male sexual differentiation of crustaceans. The insulin-like androgenic gland hormone (IAG), secreted from the AG, plays a central role in this axis, however key factors upstream the IAG are still poorly understood. Here, two crustacean hyperglycemic hormone (CHH) genes (LvCHH1 and LvCHH2) and their putative receptor guanylate cyclase (LvGC) were identified in Litopenaeus vannamei. LvCHH1 and LvCHH2 belonged to CHH subfamily I members and LvGC was a membrane-bound guanylate cyclase. They were all differentially expressed in eyestalks and gonads of males and females. RNA interference (RNAi) of either LvCHH1 or LvCHH2 increased LvIAG expression, while injection of their recombinant protein decreased LvIAG expression, indicating that LvCHH1 and LvCHH2 are inhibitory factors of LvIAG expression. Yeast two-hybrid assay showed that both LvCHH1 and LvCHH2 interacted with LvGC and their RNAi and recombinant protein injection exerted opposite regulatory effects on the transcriptional expression of LvGC. Meanwhile, knockdown of LvGC increased LvIAG expression. These results suggest that LvGC is the receptor of LvCHH1 and LvCHH2 and they are all involved in male sexual development by regulating LvIAG expression. The present study unveils missing upstream elements in the “eyestalk-AG-testis” endocrine axis in crustacean.

Screening for Dmrt genes from embryo to mature Macrobrachium rosenbergii prawns

The doublesex and mab-3 related transcription factor (Dmrt) gene family is known to be related to the sexual regulators doublesex of arthropods and mab-3 of annelids and to hold highly conserved functions in sexual determination and differentiation across phyla. Here, we report a study of the Dmrt gene family in the freshwater prawn Macrobrachium rosenbergii, a crustacean whose sexual differentiation has been widely researched. A wide transcriptomic screen, from the embryo to the adult M. rosenbergii, identified five novel Dmrt genes (MroDmrts) and confirmed two known MroDmrts. The seven MroDmrts encode proteins of 275-855 amino acids; each protein contained at least one conserved DNA-binding DM domain, which is typical of Dmrt proteins, and five proteins contained 1-4 transactivation domains (TADs). Importantly, in the embryonic, larval and post-larval stages, MroDmrt genes exhibited time-dependent expression patterns rather than sex-specific expression. In-silico screening of the expression of the MroDmrt genes in adult males revealed the enrichment of MroiDmrt1b and MroiDmrt1c in the androgenic gland (AG) as compared to the eyestalks. In vivo silencing of the androgenic gland insulin-like (IAG) encoding gene significantly decreased the expression of the above two Dmrt genes, while not affecting the expression of control genes, thereby suggesting the possible role of these two genes in the IAG-switch and in sex-differentiation processes.

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.

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