FecBB mutation enhances follicle stimulating hormone sensitivity of granulosa cells by up-regulating the SMAD1/5–USF1–FSHR signaling pathway

Abstract

The FecBB mutation, a single-point mutation (c.A746G; p.Q249R) in bone morphogenetic protein receptor type 1 B (BMPR1B), is associated with increased ovulation quotas and litter size in sheep. However, the regulatory mechanism of the FecBB mutation in increased fecundity remains to be elucidated. Therefore, creating an immortal cell model harboring the FecBB mutation would elucidate the regulatory mechanism of this mutation. Here, we report the creation of a human granulosa cell, COV434, model containing a homozygous FecBB mutation through homology-directed repair (HDR) induced by clustered, regularly-interspaced, short palindromic repeats–CRISPR-associated protein 9 along with a single-stranded oligodeoxynucleotide (ssODN) template. We found that the FecBB mutation enhanced the basal SMAD1/5 signaling activity in COV434 cells, leading to increased expression of FSHR, probably through increased formation of the SMAD1/5–SMAD4 complex to bind to the SBE element, which in turn promotes the binding of USF1 to the regulatory element E-box in the promoter of FSHR. Furthermore, the FecBB mutation substantially enhanced estradiol (E2) synthesis in granulosa cells under follicle stimulating hormone (FSH) stimulation, indicating an enhanced sensitivity to FSH, which may promote the growth of more small follicles into mature follicles, leading to increased fecundity. Our study provides novel insights into the possible regulatory mechanisms of FecBB mutations in increased fecundity.