Transcriptome for small yellow follicles reveals bone morphogenetic protein 15 involved in chicken follicle selection

Sustaining egg production in late-laying chickens can extend their egg-laying cycle. Follicle selection is a pivotal process that determines the egg production rate, acting as the ultimate regulatory checkpoint to ensure only the most viable follicles progress to ovulation. This study aimed to identify and elucidate the role of a potential gene in follicle selection. Follicles measuring 6−8 mm were harvested from high egg-yielding (H) and low egg-yielding (L) Taihang chickens at 43 weeks of age for RNA sequencing to identify DEGs. The role of <italic>BMP15</italic> in follicle selection was investigated by adding recombinant BMP15 protein to GCs. As a result, 99 DEGs were identified, and <italic>BMP15</italic> was selected as the candidate gene for its role in follicle selection. The addition of recombinant BMP15 activated the SMAD1 signaling pathway, upregulated the expression of bone morphogenetic protein receptor type 1B (<italic>BMPR1B</italic>) and follicle-stimulating hormone receptor (<italic>FSHR</italic>), and increased cyclic adenosine monophosphate (cAMP) levels. However, BMP15 significantly repressed the expression of steroidogenic acute regulatory protein (<italic>STAR</italic>) and cytochrome P450 family 11 subfamily A member 1 (<italic>CYP11A1</italic>) and slightly decreased the progesterone (P4) levels. Furthermore, the co-administration of follicle-stimulating hormone (FSH) with recombinant BMP15 resulted in a significant decrease in <italic>BMPR1B</italic> expression and a marked increase in <italic>FSHR,</italic> <italic>STAR,</italic> and <italic>CYP11A1</italic> expression, which led to a comparable change in P4 levels. These findings demonstrated that <italic>BMP15</italic> is involved in follicle selection by enhancing <italic>FSHR</italic> expression and the cAMP level. <italic>BMP15</italic> interacts with FSH to regulate follicle selection from the pre-hierarchical to hierarchical follicles.