Molecular characterization of MSX2 gene and its role in regulating steroidogenesis in yak ( Bos grunniens) cumulus granulosa cells

Cumulus granulosa cells (CGCs) are somatic cells surrounding the oocyte that play an important role in oocyte growth, meiotic maturation, ovulation, and fertilization in mammals. Therefore, revealing the molecular mechanisms related to the development and function of CGCs is essential for further understanding the regulatory network in female reproduction. MSX2 belongs to the highly conserved msh homeobox gene family and plays diverse roles in different biological processes. This study cloned the coding sequence (CDS) of the yak MSX2 gene and detected the abundance and localization of MSX2 in the major female reproductive organs. The results indicated that the CDS of this gene included 747 base pairs and encoded 248 amino acids. The abundance of MSX2 mRNA was highly expressed in the luteal phase of the yak ovary during the estrous cycle, and MSX2 protein was widely expressed in different female reproductive organs, including the ovary, corpus luteum, uterus, and oviduct. Repressing MSX2 abundance in yak CGCs declined the cell viability and defective steroidogenesis. Several genes abundances related to cell proliferation, apoptosis, and sterogenesis also changed after MSX2 knockdown. MSX2 overexpression had the opposite effect on cell viability in yak CGCs. These results reveal the specific mechanism by which MSX2 regulates the development and function of yak CGCs and give novel and valuable insights into the mechanisms involved in yak reproduction.