Expression characteristics of the Cyp19a1b aromatase gene and its response to 17β-estradiol treatment in largemouth bass (Micropterus salmoides)

To investigate the regulatory role of the Cyp19a1b aromatase gene in the sexual differentiation of largemouth bass ( Micropterus salmoides , LMB), we obtained the full-length cDNA sequence of Cyp19a1b using rapid amplification of cDNA ends technique. Tissue expression characteristics and feedback with 17-β-estradiol (E 2 ) were determined using quantitative real-time PCR (qRT-PCR), while gonad development was assessed through histological section observations. The cDNA sequence of LMB Cyp19a1b was found to be1950 base pairs (bp) in length, including a 5' untranslated region of 145 bp, a 3' untranslated region of 278 bp, and an open reading frame encoding a protein consisting of 1527 bp that encoded 508 amino acids. The qRT-PCR results indicated that Cyp19a1b abundantly expressed in the brain, followed by the gonads, and its expression in the ovaries was significantly higher than that observed in the testes. ( P  < 0.05). After feeding fish with E 2 for 30 days, the expression of Cyp19a1b in the pseudo-females gonads (XY-F) was significantly higher than that in males (XY-M) ( P   0.05). Although the expression of Cyp19a1b in XY-F and XX-F fish was not significantly different after 60 days ( P  > 0.05), both exhibited significantly higher levels than that of XY-M fish ( P  < 0.05). Histological sections analysis showed the presence of oogonia in both XY-F and XX-F fish at 30 days, while spermatogonia were observed in XY-M fish. At 60 days, primary oocytes were abundantly observed in both XY-F and XX-F fish, while a few spermatogonia were visible in XY-M fish. At 90 days, the histological sections results showed that a large number of oocytes were visible in XY-F and XX-F fish. Additionally, the gonads of XY-M fish contained numerous spermatocytes. These results suggest that Cyp19a1b plays a pivotal role in the development of ovaries and nervous system development in LMB.