Genes that Mediate Callipyge Induced Muscle Hypertrophy

DLK1 is a primary inducer of muscle hypertrophy due to the co-localization and up-regulation with the inheritance of the callipyge mutation. Microarray analysis identified 375 genes that were differentially expressed in the semimembranosus. Analysis of gene expression by qPCR in 4 hypertrophied and 3 non-hypertrophied muscles was conducted to determine co-expression with induced DLK1to distinguish the genes that directly respond to DLK1 signaling from muscle-specific responses to hypertrophy. Five genes were consistently co-expressed with DLK1 in all hypertrophied muscles and are candidate targets of DLK1 signaling. Primary myoblasts and myotubes were treated with recombinant DLK1 as a simplified model for DLK1 signaling during myogenesis. DLK1 induced the expression of several mouse orthologs of the candidate target genes, Slc22a3, Pde4d, Dnttip1 and Mettl21e, as well as the Myh4 gene (type II, glycolytic). Transfection of a DLK1 expression plasmid caused the up-regulation of the Myh4 promoter using a luciferase assay in mouse primary myotubes. Transfection of plasmids encoding ovine DNTTIP1 and PARK7 were also able to up-regulate the Myh4/luciferase reporter. The combined analysis identified several of the differentially expressed genes that respond to DLK1 signaling and have physiological roles in myogenesis and myosin gene expression.