NR5A1 and NR5A2 regulate follicle development in chicken (Gallus gallus) by altering proliferation, apoptosis, and steroid hormone synthesis of granulosa cells

Chicken ovarian follicle development is regulated by complex and dynamic gene expression. Nuclear receptor 5A1 and 5A2 (NR5A1 and NR5A2, respectively) are key genes that regulate steroid hormone production and gonadal development in mammals; however, studies on follicular development in the chicken ovary are scarce. In this study, we investigated the functions of NR5A1 and NR5A2 on follicle development in chickens. The results showed that the expression of NR5A1 and NR5A2 was significantly higher in small yellow follicles and F5. Furthermore, the expression of NR5A1 and NR5A2 was significantly higher in follicular tissues of peak-laying hens (30 weeks) than in follicular tissues of late-laying hens (60 weeks), with high expression abundance in granulosa cells (GC). The overexpression of NR5A1 and NR5A2 significantly promoted proliferation and inhibited apoptosis of cultured GC; upregulated STAR, CYP11A1, and CYP19A1 expression and estradiol (E2) and progesterone (P4) synthesis in GC from pre-ovulatory follicles (po-GC); and increased STAR, CYP11A1, and CYP19A1 promoter activities. In addition, follicle-stimulating hormone treatment significantly upregulated NR5A1 and NR5A2 expression in po-GC and significantly promoted FSHR, CYP11A1, and HSD3B1 expression in GC from pre-hierarchical follicles and po-GC. The core promoter region of NR5A1 was identified at the −1095- to −483-bp and −2054- to −1536-bp regions from the translation start site (+1), and the core promoter region of NR5A2 was at −998 to −489 bp. Two single nucleotide polymorphisms (SNPs) were identified in the core promoter region of the NR5A1 gene, which differed between high- and low-yielding chicken groups. Our study suggested that NR5A1 and NR5A2 promoted chicken follicle development by promoting GC proliferation and E2 and P4 hormone synthesis and inhibiting apoptosis. Moreover, we identified the promoter core region or functional site that regulates NR5A1 and NR5A2 expression.