Polymorphisms of the ASIP gene and the haplotype are associated with fat deposition traits and fatty acid composition in Chinese Simmental steers

Abstract

Unlike specific expression in the skin of wild mice, the agouti signaling protein (ASIP) is expressed widely in the tissue of cattle, including adipose and muscle tissue. Hence, it has been suggested that ASIP plays a role in bovine fat metabolism. An inserted L1-BT element was recently identified upstream of the ASIP locus which led to an ectopic expression of ASIP mRNA in cattle. In this study, we detected the indel of the L1-BT element at g. $-14643$ nt and three SNPs in introns of the ASIP gene (g. $-568$ A $>$ G, g. $-554$ A $>$ T, and g. 4805A $>$ T) in a Chinese Simmental steer population. The association analysis between variants of ASIP and economic traits showed that the homozygous genotype of L1-BT element insertion, AA genotype of g. $-568$ A $>$ G, and AT genotype of g. 4805A $>$ T were significantly correlated with carcass and fat-related traits, such as live weight and back fat thickness. Moreover, three haplotypes (H1: AT; H2: AA; H3: GT) were identified by linkage disequilibrium analysis and formed six combined genotypes. Results indicated that Chinese Simmental steers with an H1H2 combined genotype had a higher measured value of fat-deposition-related traits ( $p<0.05$ ), including thickness of back fat and percentage of carcass fat coverage, but a lower content of linoleic acid and $\alpha$ -linolenic acid ( $p<0.05$ ). Individuals of an H3H3 combination had a lower marbling score, perirenal fat weight, and carcass weight ( $p<0.05$ ). This suggests that these three SNPs and two combined haplotypes might be molecular markers for beef cattle breeding selection.