TGIF1 and SF1 polymorphisms are associated with litter size in Small Tail Han sheep

TGF-β induced factor homeobox 1 (TGIF1) and splicing factor 1 (SF1) are important for mammalian reproduction; however, the effects of these genes on litter size in sheep remain unexplored. In this study, we genotyped 768 ewes from seven sheep breeds at two loci: g.37871539C>T, a synonymous mutation of TGIF1; and g.42314637T>C, a 3'UTR variant of SF1. Our analysis of polymorphism revealed only two genotypes at locus g.37871539C>T in TGIF1, with most sheep populations being moderately polymorphic (0.25 < PIC < 0.5) at this site. In contrast, most breeds exhibited low polymorphism (PIC ≤0.25) at the SF1 locus g.42314637T>C. The association analysis revealed that a synonymous mutation at g.37871539C>T in TGIF1 was highly associated with litter size in Small Tail Han sheep, in which it causes a significant decrease in litter size. Conversely, while the SF1 3'UTR variant g.42314637T>C was also highly associated with litter size in sheep, it causes a significant increase in the number of litter size. Combined, these data provide valuable information regarding candidate genetic markers for sheep breeding programs.