Expression profile of star and cyp19 and plasma sex steroid during gonad development from previtellogenesis to early atresia in captive Sterlet sturgeon, Acipenser ruthenus

The aromatase cytochrome P450 family 19 (cyp19a) and Steroidogenic acute regulatory protein (star) mRNA levels were investigated in the ovarian follicles of captive Sterlet sturgeon, Acipenser ruthenus by real‐time PCR, and also plasma sex steroid levels and cortisol were measured throughout oogenesis from previtellogenic (PV) to early atresia. Thirty two females divided into four groups including PV, vitellogenic (VTG), post‐vitellogenic (POV) and atresia by histological studies. Blood samples were captured by heparinized syringes and gonad tissue samples were taken via a non‐lethal biopsy. Expression levels of both cyp19a and star transcripts were affected by gonadal development stage. Total cyp19a and star ovarian transcripts were markedly up‐regulated at VTG and POV Sterlet sturgeon, respectively. Significant elevation of sex steroids includes 17β estradiol (E2) and testosterones (T) were found during gonadal development progression, followed by steroid concentrations decrease at follicular atresia. However, plasma cortisol levels decreased during oogenesis. A positive correlation observed between plasma E2 and T with star mRNA expression. These results reveal a strong relationship between expressions of steroidogenesis related gene with gonadal development. Therefore, it seems that these genes affect estrogen synthesis and the physiological balance among the sex steroid hormones throughout oocyte development in Sterlet sturgeon.