The Effects of Eyestalk Ablation on the Androgenic Gland and the Male Reproductive Organs in the Kuruma Prawn Marsupenaeus japonicus.

Insulin-like androgenic gland factor (IAG) is considered a key regulator of male sexual differentiation and maturation in decapod crustaceans. In several species, IAG expression is thought to be negatively regulated by the eyestalk, as demonstrated by eyestalk ablation (ESA) experiments. In the kuruma prawn Marsupenaeus japonicus, however, the upstream regulatory mechanisms of IAG (Maj-IAG) remain largely unclear. In the present study, males of different body sizes were subjected to ESA to elucidate these mechanisms. Bilateral ESA induced upregulation of Maj-IAG expression from day 7 onward, whereas unilateral ESA did not. Moreover, enhanced development of male reproductive organs and hypertrophy of the androgenic gland were observed from day 7 after bilateral ESA. These findings indicate that Maj-IAG is regulated by eyestalk-derived factor(s), supporting the presence of an eyestalk-androgenic gland endocrine axis in M. japonicus. By contrast, the expression of Maj-Dsx2, a homolog of doublesex (Dsx) that has recently been proposed as an upstream regulator of IAG, did not show a consistent increase following bilateral ESA across all experiments, suggesting that the involvement of Maj-Dsx2 in this axis remains unclear. Overall, this study provides fundamental insights into the regulatory mechanisms of decapod male reproduction.