Molecular characterization and effects of the TGIF1 gene on proliferation and steroidogenesis in yak (Bos grunniens) granulosa cells.

TG interaction factor 1 (TGIF1) plays a major role in transcriptional inhibition and suppression of TGF-β signaling, but its functional roles in granulosa cells (GCs) have not been elucidated; in particular, there is no information about the yak (Bos grunniens) TGIF1 gene. Therefore, the objectives of this study were to clone yak TGIF1 and investigate TGIF1 functions in yak GCs. RT‒PCR results showed that the coding region of yak TGIF1 is 759 bp and encodes 252 amino acids. Its nucleotide sequence showed 85.24-99.74% similarity to mouse, human, pig, goat and cattle homologous genes. To explore the functional roles of TGIF1, we studied proliferation, apoptosis, cell cycle progression, steroidogenesis and the expression levels of related genes in yak GCs transfected with small interfering RNA specific to TGIF1. The results showed that TGIF1 knockdown promoted proliferation and cell cycle progression and inhibited apoptosis and estradiol (E) and progesterone (P) production in cultured yak GCs. Conversely, TGIF1 overexpression inhibited proliferation and cell cycle progression and stimulated apoptosis and E and P production. In addition, these functional changes in yak GCs were observed parallel to the expression changes in genes involved in the cell cycle (PCNA, CDK2, CCND1, CCNE1, CDK4 and P53), apoptosis (BCL2, BAX and CASPASE3), and steroidogenesis (CYP11A1, 3β-HSD and StAR). In conclusion, TGIF1 was relatively conserved in the course of animal evolution. TGIF1 inhibited GC viability and stimulated apoptosis and the secretion of E and P by yak GCs. Our results will help to reveal the mechanism underlying yak follicular development and improve the reproductive efficiency of female yaks.