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

Fang Liu,Wenyuan Shi,Haihui Ye,An Liu,Zhihuang Zhu

doi:10.3389/fmars.2021.666763

Abstract

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.

Highlights

Gonochorism is the most common reproductive strategy in decapod crustacean species (Juchault, 1999)
The reproductive system of male American lobster Homarus americanus consists of the paired testes, vas deferens, spermiducts, and gonopores located on the fifth pair of walking legs
We continuously explored the putative function of Lvit-IAG2 in L. vittata

Summary

Introduction

Gonochorism is the most common reproductive strategy in decapod crustacean species (Juchault, 1999). Males and females have significantly different reproductive systems, as well as external features (Nagaraju, 2011). The reproductive system of male American lobster Homarus americanus consists of the paired testes, vas deferens, spermiducts, and gonopores located on the fifth pair of walking legs. The specialized first pair of pleopods serves as a gonopod during mating (Comeau and Benhalima, 2018b). The female reproductive system of H. americanus consists of the paired ovaries, oviducts, and gonopores located on the third pair of walking legs. The specialized organ, seminal receptacle, arises on the thoracic ventral side between the fourth and the fifth pairs of walking legs (Comeau and Benhalima, 2018a)

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Conclusion