Two completely linked polymorphisms in the PPARG transcriptional regulatory region significantly affect gene expression and intramuscular fat deposition in the longissimus dorsi muscle of Erhualian pigs

This article is the first to report the significant effect of PPARG promoter polymorphisms on the expression and intramuscular fat (IMF) content in the longissimus dorsi (LD) muscle of Erhualian pigs. Polymorphic sites for the PPARG upstream transcriptional regulatory region were scanned by direct sequencing of two DNA pools consisting of individuals with significantly different IMF content (P < 0.05). Two SNPs (c.-1633C>T and c.-1572G>A) were identified, with different allele distribution between these two groups. A total of 66 Erhualian pigs and 24 Yorkshire × Large White (Y × L) pigs were genotyped for these two SNPs using PCR-SSCP (single-strand conformation polymorphism), which exhibited that only the T-A and C-G haplotypes existed. The T-A type promoter was found to have higher activity than G-C type promoter for PPARG gene transcription in the induced preadipocytes using luciferase assay. In addition, the frequency of the T-A type in Erhualian pigs was much higher than that in the Y × L pigs (35.6% vs. 8.3%), and in fact, no T-A/T-A samples were found in Y × L pigs. Therefore, we conclude that the T-A haplotype of PPARG is a desirable form that might contribute to the relatively higher IMF content in Erhualian pigs.