The Effects of Eyestalk Ablation on the Androgenic Gland and the Male Reproductive Organs in the Kuruma Prawn <i>Marsupenaeus japonicus</i>

Insulin-like androgenic gland factor (IAG) is considered a key regulator of male sexual differentiation and maturation in decapod crustaceans. In several species, <i>IAG</i> expression is thought to be negatively regulated by the eyestalk, as demonstrated by eyestalk ablation (ESA) experiments. In the kuruma prawn <i>Marsupenaeus japonicus</i>, however, the upstream regulatory mechanisms of <i>IAG</i> (<i>Maj-IAG</i>) 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 <i>Maj-IAG</i> 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 <i>Maj-IAG</i> is regulated by eyestalk-derived factor(s), supporting the presence of an eyestalk–androgenic gland endocrine axis in <i>M. japonicus</i>. By contrast, the expression of <i>Maj-Dsx2</i>, a homolog of doublesex (<i>Dsx</i>) 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 <i>Maj-Dsx2</i> in this axis remains unclear. Overall, this study provides fundamental insights into the regulatory mechanisms of decapod male reproduction.