Improvement of Livestock Breeding Strategies Using Physiologic and Functional Genomic Information of the Muscle Regulatory Factors Gene Family for Skeletal Muscle Development

A defined number of skeletal muscle fibers are formed in two separate waves during prenatal development, while postnatal growth is restricted to hypertrophic muscle fiber growth. The genes of the MRF (muscle regulatory factors) gene family, consisting of 4 structurally related transcription factors - myogenin, MyoD1, myf-5, and MRF4 - regulate both skeletal muscle fiber development and postnatal hypertrophic growth. In meat producing animals, skeletal muscle tissue becomes meat after slaughtering. Skeletal muscle fibers are the major cell type of meat mass. Thus, differences in the activity of the MRF gene family may be very important for the amount of meat deposited in these animals, which is of major economic importance. Therefore, the MRF genes can be considered as potential candidate genes to investigate the relation between genomic variation in these genes and skeletal muscle mass, and thus meat mass. In this review we discuss the MRF gene family in relation to meat production, and show that information of genomic variation in these functional genes, and variation in their expression provide information that can be used in commercial breeding. Furthermore, we will review experiments that show that hormones, growth factors, and specific drugs can affect the expression of these genes, thus potentially affecting skeletal muscle mass and thus meat mass, offering several potential strategies for steering of meat production, and showing the power of functional genomics. Using the genetic information available from these experiments, ways to speed up genetic improvement of livestock breeding and future research directions will be highlighted. Keywords: skeletal muscle fibers, mrf muscle regulatory factors, Knock out, Myogenin, myf, MyoD, Mrf