Abstract：Abstract Reproductive performance is an important economic trait in sheep (Ovis aries). The study of its molecular mechanism is also extremely important. Reproductive performance of sheep is regulated by the hypothalamic-pituitary-gonad reproductive axis, and is also controlled by many growth factors. KITLG acting as ligand of KIT (KIT LIGAND, KL or KitL), as an important growth regulation factor, plays a key role in follicular development. The current study aimed to analyze the expression of KITLG gene and SNPs as well as their association with litter size in sheep, and to offer a reference data for the candidate gene research of reproduction trait in sheep. Therefore, Real time-PCR was conducted to investigate the expression patterns of KITLG gene in hypothalamus, pituitary, ovary, heart, muscle, lung, kidney, liver, spleen, duodenum, fat and rumen tissues of Hu sheep, and restriction fragment length polymorphism (RFLP) technologies were carried out to screen SNPs and analyze their association with litter size in sheep population of Hu sheep and Small tail Han sheep. The results revealed that KITLG gene expressed in heart, liver, spleen, lung, kidney, rumen, duodenum, muscle, fat, hypothalamus, pituitary, and the expression in ovary was high. According to PCR-RFLP technologies, two polymorphisms g.38473C＞T and g.47468C＞T2 were identified in intron 2 and 5 of KITLG gene respectively. In g.38473C＞T locus, two genotypes, CC and CT were found in both Hu sheep and Small tail Han sheep. Of them, CC was the dominant genotype, and C was the dominant allele. In addition, the homozygosity (Ho), heterozygosity (He), effective allele number (Ne), polymorphic information content (PIC) were 0.89, 0.11，1.31 and 0.11 for Hu sheep, and were 0.80, 0.20, 1.10 and 0.16 for Small tail Han sheep, respectively. The χ2 test indicated that Small tail Han sheep and Hu sheep populations were in Hardy-Weinberg equilibrium. Same as g.38473C＞T locus, two genotypes, CT and TT were identified in g.47468C＞T locus in both Hu sheep and Small tail Han sheep. Of which, TT was the dominant genotype, and T was the dominant allele. The Ho, He, Ne, PIC were 0.95, 0.05, 1.06, 0.05 for Hu sheep, and were 0.91, 0.09, 1.10 and 0.09 for Small tail Han sheep, respectively. The χ2 test indicated that Small tail Han sheep population and Hu sheep were all in Hardy-Weinberg equilibrium. The association analysis of polymorphisms in KITLG gene with litter size revealed that g.47468C＞T was significantly correlated with litter size in Hu sheep and Small tail Han sheep (P＜0.05). In summary, this study indicated that expression of KITLG gene in ovary was high. SNP (g.47468C>T) of KITLG gene was associated with litter size in Small tail Han sheep, and this gene could be used as a candidate gene for litter size selection at early stage of growth. This study provides a scientific basis for searching molecular markers associated with reproductive traits of the sheep, and setting breeding strategies, as well as improving the production performance of sheep. Compared with traditional breeding methods of sheep, the reaching results can also be used as a marker-assisted selection to greatly improve the breeding speed, and to achieve greater genetic progress in sheep.
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