Hormonal regulation and expression dynamics of Bmp4 in the reproductive cycle of Pampus argenteus

As a member of the bone morphogenetic protein (BMP) family, Bmp4 plays a crucial role in bone formation, early developmental stage and the regulation of gonadal development. This study aims to investigate the expression patterns and potential functions of the Bmp4 in Pampus argenteus during its reproductive cycle. A systematic evolutionary analysis of the Bmp4 was performed, and its expression was quantified and localized using real-time polymerase chain reaction (PCR), Western blotting and immunohistochemistry. Additionally, the effects of various hormones on hormone-related genes were analysed in vitro using cultured testes, ovaries and oocytes. The results revealed that Bmp4 is evolutionarily conserved and broadly expressed across tissues. Notably, its expression significantly increased at 4 and 13 days post-hatching (dph), with no significant differences observed at other developmental stages. Western blotting identified a specific Bmp4 target band in Stage III ovaries, and immunohistochemistry localized Bmp4 expression in oogonia, oocytes and spermatogonia. In vitro hormonal treatments demonstrated that oestradiol (E2) significantly upregulated bmp4 expression in both testes and ovaries, with expression levels being notably higher in ovaries. In immature vitellogenic oocytes cultured in vitro, sex hormone treatments did not significantly affect the expression of bmp4, lhr, fshr and lhβ. However, under LH + hCG treatment (50 ng/mL and 5 IU/mL), the expression of fshβ was upregulated. In summary, our findings reveal that Bmp4 serves as a pivotal factor in the early development of the gonads and germ cells in P. argenteus. The expression of Bmp4 within the ovary is likely regulated by E2. During the early-stage development of the ovary, E2 and Bmp4 may jointly promote the early-stage development and differentiation of germ cells. This study offers a valuable theoretical foundation for addressing challenges in the breeding process.