Results
Peroxisome Proliferator Activated Receptor-γ
Peroxisome Proliferator Activated Receptor-gamma (PPARγ) is a member of the nuclear receptor superfamily (for review see Green, 1995) and regulates the expression of several genes encoding proteins involved in adipocyte differentiation (Rosen et al., 2000; Spiegelman et al., 1997) and fat deposition (for review see Schoonjans et al., 1996). Genetic mutations in PPARγ have been found to be associated with extreme obesity in humans (Freake, 1999). In pigs, PPARγ expression levels in adipose tissue vary among different breeds and ages (Grindflek et al., 1998). An association study (Grindflek, in manuscript), reported a difference in loin fatty acid composition in Norwegian pigs for a BsrI PCR-RFLP, but no significant differences were noted for backfat or intramuscular fat measurements.
Our results show that a BsrI PPARγ PCR-RFLP (Grindflek, personal communication) was polymorphic in Berkshire, Duroc, Landrace, and Hampshire populations. The frequency of allele 1 was 0.81. Total population analysis revealed effects (P<0.05) on off flavor score (Table 1), although interesting trends in average daily gain, tenderness and juiciness approached significance. The results of the individual breed analysis (not shown) revealed differences (P<0.05) between PPARγ genotypes and loin muscle area and marbling for Duroc, average daily gain for Hampshire; and last rib backfat, and Instron tenderness for Landrace.
This PPARγ PCR-RFLP remains an interesting candidate gene for meat quality traits within specific lines of swine. These results, while promising, warrant larger scale investigation to determine the potential use of PPARγ in future selection programs.