Ovine TUSC5 and IGFBP3 Gene Polymorphisms and their Association with Tail Fat Weight in Sheep

Tail fat weight is a key economic trait in fat-tailed sheep; reducing tail fat deposition is of significant importance for improving the economic efficiency of sheep farming. In this article, we measured the live weight before slaughter, tail fat weight, and carcass weight of Hu male sheep at 6 months of age and performed the descriptive statistical analysis. The results indicated the coefficient of variation of tail fat-related-traits ranged from 25% to 50%. Simultaneously, we selected IGFBP3 and TUSC5 as candidate genes based on their close association with fat deposition. Target regions were amplified using gene-specific primers in PCR, followed by Sanger sequencing of PCR products to identify genetic variants. Polymorphisms were subsequently validated using the KASPar genotyping assay. Finally, quantitative reverse transcription PCR (qRT-PCR) was performed to determine the expression levels of IGFBP3 and TUSC5. Our findings revealed a missense mutation (g.83695349 C>T) in exon 1 of the IGFBP3 gene and a synonymous mutation (g.41771645 C>T) in exon 2 of the TUSC5 gene. Association analysis showed that these mutations were significantly correlated (p < 0.05) with tail fat weight traits. Moreover, the tail fat weight of the mutant genotypes (CT and TT) was significantly reduced compared with that of the CC genotype, suggesting that the gene may exert a negative regulatory effect on this trait, thereby leading to the reduction of tail fat weight. Furthermore, the genotype combinations showed a significant relationship with tail fat traits. Moreover, qRT-PCR results showed that TUSC5 and IGFBP3 genes were expressed in all experimental tissues of Hu sheep, and the highest expression was observed in tail fat compared with other tissues (heart, liver, spleen, lung, kidney, rumen, duodenum, muscle, and lymph). Notably, their expression levels were significantly lower in the large-tail fat group than in the small-tail fat group. Overall, these results will provide novel candidate variation for reducing tail fat deposition in sheep breeding practice.