Expression of GnIH and its effects on follicle development and steroidogenesis in quail ovaries under different photoperiods.

Photoperiod is an important environmental factor that influence seasonal reproduction behavior in bird and GnIH can play a function in this process through the reproductive axis, and some studies suggest that GnIH may have a direct role at the gonadal level. To investigate the expression of GnIH and its effects on follicle development and steroidogenesis in quail ovaries under different photoperiods, 72 healthy laying quails of 8-wk-old were randomly divided into long day (LD) group [16 light (L): 8 dark (D)] (n = 36) and short day (SD) group (8L:16D) (n = 36). Samples were collected from each group on d1, d11, d22, and d36 of the experiment. The result showed that short day treatment upregulated the level of GnIH in the gonads (P < 0.05), decreased the expression level of CYP19A1,3β-HSD, StAR, LHR, and FSHR and increased the expression level of AMH, AMHR2, GDF9, and BMP15 to inhibit follicle development and ovulation, thus affecting the egg production performance of quails. In vitro culture of quail granulosa cells and treatment with different concentrations of GnIH (0, 1, 10, and 100 ng/mL) for 24 h. Result showed that GnIH inhibited the levels of FSHR, LHR, and steroid synthesis pathways in granulosa cells, upregulated the levels of AMHR2, GDF9, and BMP15. The results suggest that the inhibition of follicle development and reduced egg production in quail by short day treatment is due to GnIH acting at the gonadal level, and GnIH affected the steroid synthesis by inhibiting gonadotropin receptors.