Porcine intramuscular fat content and composition are regulated by quantitative trait loci with muscle-specific effects

Intramuscular fat (IMF) storage is a biological process with strong impact on nutritional and technological properties of meat, and also with relevant consequences on human health. The genetic architecture of IMF content and composition phenotypes has been thoroughly studied in pigs through the identification of quantitative trait loci (QTL) and the estimation of genetic parameters. A question that has not been elucidated yet is if the genetic determinants of IMF-related phenotypes are muscle specific or, conversely, they have broad effects on the whole skeletal muscle compartment. We have addressed this question by generating lipid QTL maps for two muscles with a high commercial value, gluteus medius (GM) and longissimus thoracis et lumborum (LTL), in a Duroc commercial population (N=350). As a complementary approach, we have analysed the mRNA expression pattern of both muscles at a whole genome scale. The lack of concordance between the GM and LTL QTL maps evidenced that the effects of polymorphisms influencing IMF, cholesterol and fatty acids contents are modulated to some extent by complex spatial factors related with muscle location, metabolism and function. This interpretation was supported by our finding that genes influencing cell differentiation, muscle development and function and lipid metabolism are differentially expressed between muscles. These results have important implications on the implementation of genomic selection schemes aimed to improve the lipid profile of swine meat. Moreover, they confirm pigs as a valuable model to dissect the genetic basis of muscle lipid phenotypes of clinical interest in human.

19