Vitamin D3 promotes fish oocyte development by directly regulating gonadal steroid hormone synthesis.

Vitamin D receptors (VDR) and vitamin D3 metabolizing enzymes have been found to be highly expressed in the ovaries and spermatophores of fish. However, the role of VD3 on fish gonadal development has rarely been reported. In this study, two-month-old female zebrafish were fed with different concentrations of VD3 diets (0 IU/kg, 700 IU/kg, 1400 IU/kg, and 11,200 IU/kg) to investigate the effects of VD3 on ovarian development. The diet with 0 IU/kg VD3 resulted in elevated interstitial spaces, follicular atresia and reproductive toxicity in zebrafish ovaries. Supplementation with 700 IU/kg and 1400 IU/kg of VD3 significantly increased oocyte maturation rate, upregulated ovarian gonadal steroid hormone synthesis capacity, and elevated plasma estradiol (E2), testosterone (T) and ovarian vitellogenin (VTG) levels. Furthermore, the current study identified a vitamin D response element (VDRE) in the cyp19a1a promoter and demonstrated that 1.25(OH)2D3-VDR directly activated cyp19a1a production through activating VDRE. In conclusion, this study shows that an appropriate concentration of VD3 can promote zebrafish ovarian development and affect VTG synthesis through the vdr/cyp19a1a/er/vtg gene axis.