Abstract：Abstract Litter size is one of the most important economic traits in sheep (Ovis aries) which is controlled by minorgenes. While genes that have been found to be related to litter size are numbered, and it is still a hotspot to mine them. To investigate the tissue expression level and polymorphisms of follistatin-like protein 1 gene (FSTL1) which is found by whole genome re-sequencing (WGS) and its association with litter size in sheep, semi-quantitative reverse transcription and polymerase chain reaction (sqRT-PCR) and quantitative real-time PCR (qRT-PCR) were performed to investigate the expression of FSTL1 gene in sheep with different lambing abilities. Multiparous (380 Small Tail Han sheep) and uniparous (total 380 for Tan, Sunite, Suffolk, Dorper and Prairie Tibetan sheep) sheep breeds were selected and Sequenom MassARRAY?SNP assay was applied to genotype four single nucleotide polymorphism sites (SNPs) of FSTL1 gene. Then the association was analyzed between FSTL1 and litter size in Small Tail Han sheep. The results showed that FSTL1 expressed in all tissues selected. qRT-PCR indicated that the expression of FSTL1 had no significant difference between uniparous and multiparous sheep (P＞0.05), but the expression in pituitary, ovary, oviduct, uterus body and uterine horn of uniparous Sunite sheep was higher than that in multiparous Small Tail Han sheep, and the expression in pituitary, oviduct and uterus body of ++ was significantly higher than those in BB and B+ (P＜0.05). From genotyping, this study found the genotype frequencies and allele frequencies of the four SNPs were significantly different between uniparous and multiparous sheep (P＜0.05). Population genetic analysis showed that four SNPs were at moderate polymorphism in Small Tail Han sheep (0.25＜PIC＜0.5) and partial at moderate (0.25＜PIC＜0.5) and partial at low polymorphism (PIC＜0.25) in other sheep breeds. The χ2 test indicated that, the four SNPs were under Hardy-Weinberg equilibrium (P＞0.05) in most of the sheep breeds that chose. Association analysis indicated that the polymorphisms of the four SNPs in FSTL1 had no significant correlation with the litter size of each parity in Small Tail Han sheep (P＞0.05), and the litter size of mutation homozygotes was lower than that of wild homozygotes for almost all SNPs. Therefore, the results concluded that there may be a certain negative correlation between the expression level of FSTL1 and the litter size in sheep, but the four SNPs have no significant association with the litter size of different parities of Small Tail Han sheep (P＞0.05), which indicated they may not be the key loci that affect the expression or function of FSTL1. This study might provide a basis for litter size trait selection in sheep.
