The Regulatory Relationships Between the Gonad-Inhibiting Hormone and Insulin-Like Androgenic Gland Hormone-Binding Protein Genes in the Eyestalk-Androgenic Gland-Testis Axis of Macrobrachium rosenbergii

Gonad-inhibiting hormone (GIH) belongs to a family of neuropeptides that are released from the eyestalks of male crustaceans and plays key roles in gonadal maturity, reproduction, and molting. However, the detailed mechanisms underlying the effects of GIH on sexual regulation have yet to be elucidated. In the present study, we aimed to demonstrate how GIH mediate the activity of the androgenic gland (AG) to affect sexual regulation. To do this, we cloned and characterized a GIH sequence from Macrobrachium rosenbergii (MrGIH). The open reading frame (ORF) of MrGIH was 360 bp and codes for a polypeptide of 119 amino acids and a putative protein of 13.56 KDa. Tissue analysis showed that MrGIH is widely expressed in a range of tissues but particularly, the eyestalk, intestine, and nerve cord. Following the dsRNA silencing of MrGIH for 24 h, the expression levels of MrGIH were down-regulated in both the eyestalk and AG when compared with the negative control, but significantly increased the expression of Macrobrachium rosenbergii insulin-like androgenic gland hormone-binding protein (MrIAGBP) in AG, thus suggesting that MrGIH is an inhibitory factor for MrIAGBP. In addition, we found that eyestalk removal on certain days led to increased expression levels of MrIAGBP expression. The expression levels of MrIAGBP peaked at 2 d in the AG after unilateral and bilateral eyestalk ablation, exhibiting a 7.27- and 6.03-fold increase, respectively. Afterward, the expression of GIH protein levels were down-regulated and IAGBP protein levels were up-regulated after GIH silencing using immunohistochemistry method, combined with the increase of IAGBP protein levels after eyestalk ablation, confirming that MrGIH is an inhibitory factor that can moderately regulate AG development and IAGBP expression. Collectively, our findings enriched the mechanisms that control the sexual regulation pathway of male M. rosenbergii, and provided significant information for further explorations of the mechanism underlying sex regulation in other decapod crustaceans.

RNAi Reveals Role of Insulin-Like Androgenic Gland Hormone 2 (IAG2) in Sexual Differentiation and Growth in Hermaphrodite Shrimp

Insulin-like androgenic gland hormone (IAG) is the most widely known hormone that regulates sexual differentiation in crustaceans. Previously, a transcriptome study described two transcripts of IAGs (Lvit-IAG1 and Lvit-IAG2) in the peppermint shrimp Lysmata vittata, a species characterized by a rare reproductive system of protandric simultaneous hermaphroditism (PSH). Herein, we explored the function of Lvit-IAG2 via RNA interference (RNAi) experiments, and then compared the functional differences between the two IAGs. We demonstrated that Lvit-IAG2 positively regulated the expression of crustacean hyperglycemic hormone (Lvit-CHH) in eyestalk ganglion but exhibited no significant effect on the expression of gonad-inhibiting hormone (Lvit-GIHs) and crustacean female sex hormone (Lvit-CFSHs). Besides, Lvit-IAG2 gene knockdown caused degeneration in appendices masculinae (AM) and suppressed germ cells at the secondary spermatocyte stage. Moreover, silencing the Lvit-IAG2 gene impeded ovarian development, including smaller previtellogenic oocytes, and lower expression of vitellogenin (Lvit-Vg) gene in hepatopancreas and vitellogenin receptor (Lvit-VgR) gene in the ovarian region. Notably, silencing the Lvit-IAG2 gene impeded individual growth of the species. Collectively, findings from this study demonstrate that Lvit-IAG2 and Lvit-IAG1 coordinatively function to modulate sexual differentiation in L. vittata; meanwhile, Lvit-IAG2 stimulates the growth of the PSH species.

Roles of gonad-inhibiting hormone in the protandric simultaneous hermaphrodite peppermint shrimp†

To date, the molecular mechanisms of the unique gonadal development mode known as protandric simultaneous hermaphroditism (PSH) are unclear in crustaceans. In this study, cDNA of a gonad-inhibiting hormone (Lv-GIH1) was isolated from the PSH peppermint shrimp Lysmata vittata, and its expression was exclusively found in the eyestalk ganglion. Real-time quantitative polymerase chain reaction (qRT-PCR) revealed that the expression of Lv-GIH1 increased during gonadal development of the functional male stages but decreased significantly at subsequent simultaneous hermaphroditism stage. Further in vitro experiment showed that recombinant GIH1 protein (rGIH1) effectively inhibited Vg expression in the cultured hepatopancreas tissues while the short-term injection of GIH1-dsRNA resulted in reduced expression of Lv-GIH1 and upregulated expression of Vg in the hepatopancreas. Moreover, long-term rGIH1 injection led to significantly reduced expression of Lv-Vg, Lv-VgR, and Lv-CFSH1, subdued growth of oocytes, and feathery setae as a secondary sexual characteristic in females. Interestingly, while germ cells in testicular part were suppressed by rGIH1 injection, the expression of Lv-IAGs showed no significant difference; and long-term GIH1-dsRNA injection results were contrary to those of rGIH1 injection. Taken together, the results of this study indicate that Lv-GIH1 is involved in gonadal development and might also participate in controlling secondary sexual characteristic development in L. vittata by inhibiting Lv-CFSH1 expression.