A Poly(dA:dT) Tract in the IGF1 Gene Is a Genetic Marker for Growth Traits in Pigs

Simple Summary: Insulin-like growth factor 1 (IGF1) promotes mammalian development and growth. The poly(dA:dT) tract usually acts as a promoter element to regulate gene transcription. In this study, it was found that the length of a poly(dA:dT) tract in the porcine IGF1 promoter can regulate gene expression in vivo. Moreover, this polymorphism is associated with porcine growth traits (days to 115 kg and average daily gain). These results suggest that the poly(dA:dT) tract is a genetic marker for porcine growth traits. Insulin-like growth factor 1 (IGF1) is an important regulator of body growth, development, and metabolism. The poly(dA:dT) tract affects the accessibility of transcription factor binding sites to regulate transcription. Therefore, this study assessed the effects of two poly(dA:dT) tracts on the transcriptional activity of porcine IGF1. The luciferase assay results demonstrated that the poly(dA:dT) tract 2 (-264/-255) was a positive regulatory element for IGF1 gene expression, and the activities between the different lengths of the poly(dA:dT) tract 2 were significant (p < 0.01). The transcription factor C/EBP alpha inhibited the transcription of IGF1 by binding to tract 2, and the expression levels between the lengths of tract 2 after C/EBP alpha binding were also statistically different (p < 0.01). Only the alleles 10T and 11T were found in the tract 2 in commercial pig breeds, while the 9T, 10T, and 11T alleles were found in Chinese native pig breeds. The allele frequencies were in Hardy-Weinberg equilibrium in all pig breeds. The genotypes of tract 2 were significantly associated with the growth traits (days to 115 kg and average daily gain) (p < 0.05) in commercial pig breeds. Based on these findings, it can be concluded that the tract 2 mutation could be applied as a candidate genetic marker for growth trait selection in pig breeding programs.