Yongjing Li, Yujiao Jin, Yuqi Li, Yufeng Xu, Xuejun Li, Limin Wu
Steroid hormones regulate ovarian development, but hsd3b7 function in fish remains unclear. In this study, we cloned full-length hsd3b7 cDNA from Qihe gibel carp (Carassius gibelio var. Qihe) and generated a polyclonal antibody. Real-time PCR, Western blotting, and immunohistochemistry revealed widespread hsd3b7 expression in brain, heart, spleen, muscle and ovary. During ovarian development and maturation, hsd3b7 mRNA expression peaked at 150 days after hatching (dah) and remained at a relatively high level until 720 dah. Immunohistochemical analysis further revealed that Hsd3b7 protein was localized in both gonadal germ cells and somatic cells, suggesting its involvement in ovarian development and maturation. To further investigate its function, hsd3b7 was knocked down for 30 days by ovarian injection of double-stranded RNA (dsRNA) during the previtellogenic stage. Silencing of hsd3b7 markedly inhibited ovarian development, with most oocytes remaining at phase II. In addition, the expression levels of the germ cell marker genes vasa and piwil, as well as the cell proliferation-related genes pcna and ki-67, were significantly reduced. Protein interaction analysis suggested that Hsd3b7 is associated with several steroidogenic enzymes, including Cyp19a1a, Cyp11c1, Hsd17b3, and Hsd17b7. Moreover, hsd3b7 knockdown altered the expression of genes involved in steroidogenesis and lipid accumulation, and significantly affected serum E2 and total cholesterol levels. Collectively, these findings indicate hsd3b7 regulates ovarian development and maturation via steroid hormone synthesis and lipid metabolism, providing insights for addressing precocious maturation in Qihe gibel carp.