Abstract
The insulin-like androgenic gland hormone (IAG) plays a key role in male sexual differentiation and spermatogenesis in crustaceans. The expression of IAG is usually negatively regulated by neuropeptide hormones through the “eyestalk-AG” endocrine axis. However, the underlying mechanism is still largely unknown. In the present study, we performed a comparative transcriptome analysis on the androgenic gland (AG), the main secretory organ of IAG, of L. vannamei before and after unilateral eyestalk ablation. A total of 67 differentially expressed genes (DEGs) were identified, including some putative genes involved in sexual development. Interestingly, several genes related to molting and endocrine processes were found differentially expressed between the two treatments. Further investigation on the expression profiles of these genes and Lv-IAG showed that their expression patterns were closely correlated throughout the molting cycle. In addition, injection of 20-hydroxyecdysone (20E) could inhibit the expression of Lv-IAG at different molting stages in a dosage-dependent manner. The data indicated that ecdysteroids played important roles in regulating the Lv-IAG expression and might bridge the endocrine axis between eyestalk and AG. The present study provided new insights into understanding the regulation of sexual development in male crustacean.
Highlights
Sexual dimorphism is a common phenomenon in decapod crustaceans [1]
The results showed that a low dosage (1 μg) of 20E injection could inhibit the expression of Lv-insulin-like androgenic gland hormone (IAG) at pre-molt and post-molt stages, and high dosage (5 μg) of 20E injection could significantly decrease the expression levels of Lv-IAG throughout the whole molting cycle (Figure 3A)
More and more evidence indicates that the “eyestalk-androgenic gland (AG)-testis” endocrine axis in crustaceans plays an important role in regulating male sexual development by secreting peptide hormones from the X-organ/sinus-gland (XO-SG) complex of eyestalk [15]
Summary
Sexual dimorphism is a common phenomenon in decapod crustaceans [1]. Litopenaeus vannamei is one of the most successful commercial crustaceans in the world due to its high growth rate, resistance to diseases, and environmental stress, and adaptability to low salinity cultivation [2]. The female L. vannamei shows obvious superiority in growth rate comparing to male shrimp after sexual maturity [3]. The androgenic gland (AG) is an essential player in male sex differentiation processes. The insulin-like androgenic gland hormone (IAG), which is secreted by AG, is regarded as the sexual “IAG-switch” during sex differentiation of crustaceans [4]. Except for its function in sex differentiation at the early developmental stage, IAG plays important roles in the maintenance of male characters and spermatogenesis at the Sample eAG1 eAG2 eAG3 cAG1 cAG2 cAG3 adult stage of male crustaceans [6,7,8,9]. The implantation of AG or injection of an active extract of AG induces masculinization and inhibits the development of female secondary sex characteristics in crustaceans [10,11]
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