Retinoic acid promotes meiotic and germ cell differentiation programs in protandrous yellowfin seabream (Acanthopagrus latus)

Retinoic acid (RA) is a conserved regulator of germ cell differentiation, but its role in protandrous hermaphroditic fishes with anatomically distinct ovarian and testicular regions remains poorly understood. Here, juvenile yellowfin seabream ( Acanthopagrus latus ) were exposed to RA treatment, and gonadal development was examined after 30, 60 and 90 days. Histological analysis showed that primary spermatocytes appeared in the testicular region of both control and RA-treated fish at day 90, whereas a small number of primary oocytes were detected only in the ovarian region of RA-treated fish, indicating that RA treatment preferentially promoted ovarian germ cell progression. Transcriptomic analysis identified 1276, 8172 and 989 differentially expressed genes between control and RA-treated gonads at 30, 60 and 90 days, respectively, indicating a strong stage specific response, with the most extensive reprogramming at day 60. RA treatment induced early activation of retinoid, calcium and MAPK related pathways, followed by neuroendocrine, steroidogenic and meiotic programs. Key meiotic genes ( sycp3 , dmc1 , dazl and rec8 ) and sex differentiation genes ( foxl2 , dmrt1 , sox9a and cyp19a1a ) were upregulated at day 60 in RA-treated fish, supporting earlier molecular activation of reproductive developmental programs. In parallel, RA degrading enzymes ( cyp26a1 and cyp26b1 ) were strongly induced at day 30, whereas aldh1a2 showed higher expression in controls, suggesting feedback regulation of RA availability. Heatmap and PPI analyses further linked RA metabolism with steroidogenesis, meiotic progression and sex differentiation. These findings indicate that RA treatment promotes germ cell differentiation and advances reproductive developmental programs in the ovotestis of yellowfin seabream, with the most evident histological response in the ovarian lineage, and suggest that RA bioactivity is constrained by a metabolic feedback checkpoint during ovotestis development.