Abstract：The current study aimed at analyzing gene expression of tyrosine kinase A(TrkA) gene and SNPs as well as their association with litter size in sheep (Ovis aries), and thus to offer a reference data for the candidate gene research of reproduction trait in sheep. Therefore, the qRT-PCR was conducted to investigate the expression patterns of TrkA gene in heart, liver, spleen, lung, kidney, rumen, duodenum, longissimus dorsi muscle, fat, hypothalamus, pituitary and ovarian tissues of Hu sheep, and DNA pooling sequencing and restriction fragment length polymorphism (RFLP) were carried out to screen SNPs and their association with litter size in sheep population of Hu sheep (n=526) and Small tail han sheep (n=437). The results revealed that TrkA gene showed the highest expression in ovary, lung and liver which was significantly higher (P＜0.05) than that in spleen, kidney, rumen, duodenum, longissimus dorsi muscle, fat, hypothalamus, pituitary tissues of Hu sheep, and the expression in heart was in the middle expression level. The lowest expression level was observed in spleen, kidney, rumen, duodenum, longissimus dorsi muscle, fat, hypothalamus, pituitary. According to DNA pooling sequencing and RFLP technologies, 2 polymorphisms, NC_019458.2:g.105281586C＞T and NC_019458.2:g.105284248G＞C were identified in intron 9 and intron 14 of TrkA gene, respectively. In NC_019458.2: g.105281586C＞T locus, 3 genotypes, CC, CT and TT were found in both Hu sheep and Small tail han sheep. CT 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) for Hu sheep were 0.50, 0.50, 1.99 and 0.37, respectively, and were 0.49, 0.51, 1.95 and 0.37 for Small tail han sheep, respectively. The χ2 test indicated that Small tail han sheep population deviated Hardy-Weinberg equilibrium, while Hu sheep was in Hardy-Weinberg equilibrium. Same as NC_019458.2:g.105281586C＞T locus, 3 genotypes, GG, GC and CC were identified in NC_019458.2:g.105284248G＞C locus in both Hu sheep and Small tail han sheep. Of which, GC was the dominant genotype, and C was the dominant allele. The Ho, He, Ne, PIC for Hu sheep were 0.50, 0.50, 2.00 and 0.37, respectively, and were 0.49, 0.51, 1.96 and 0.37 for Small tail han sheep, respectively. In contrast, the χ2 test indicated that Hu sheep population deviated Hardy-Weinberg equilibrium, while Small tail Han sheep population was in Hardy-Weinberg equilibrium. The association analysis of polymorphisms in TrkA gene with litter size revealed that NC_019458.2: g.105281586C＞T was significantly correlated with litter size in Hu and Small tail Han sheep (P＜0.05), and NC_019458.2:g.105284248G＞C was significantly associated with litter size in Hu sheep (P＜0.05). In summary, this study indicated that expression of TrkA gene in ovary and lung was higher than remaining tissues in addition to liver. SNPs of TrkA gene associated with litter size in sheep could be used as a candidate gene for litter size selection of sheep at early stage of growth. This study provides a scientific basis for searching molecular markers associated with reproductive traits, and setting breeding strategies, as well as improving the production performance of sheep.
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