Identification of amh and its potential signaling pathway involved in the ovary development in the largemouth bass (Micropterus salmoides)

Anti-müllerian hormone (AMH), a member of the TGF-β family, plays a pivotal role in ovarian development by binding to its specific receptor, AMHR2. However, the function of amh/amhr2 pathway in fish ovarian development remains poorly understood. To elucidate its regulatory mechanism in largemouth bass, we identified amh and amhr2 genes from the largemouth bass genome and analyzed their expression patterns across different tissues and ovarian developmental stages. The results showed that amh was mainly expressed in the testis, ovary, brain and pituitary, while amhr2 was highly expressed in the testis and ovary. In vitro treatment of ovarian follicles with recombinant Amh protein increased GVBD rates of cultured oocytes, and the expression levels of amh receptors (amhr2, alk2, alk3 and alk6) and smad signaling pathway (smad1, smad5, smad8 and smad4) were significantly upregulated. Additionally, the expression of key steroidogenesis (stAR, 17βhsd, cyp17a2, cyp19a1a) and oocyte maturation-related genes (cyclin B, cdk1) were also increased. Conversely, inhibition of Amhr1 with Compound C attenuated Amh-induced upregulation of Amh receptors, SMADs, and steroidogenic genes. These findings provide novel insights into the molecular mechanisms by which the amh/amhr2 signaling pathway regulates ovarian development in largemouth bass, highlighting its role in follicular maturation and steroidogenesis.