Predominant MRF expressed in mature adult human skeletal muscle; knockdown unleashes MEF2-dependent myofiber hypertrophy
Gene Structure & Expression
Genomic Organization & Cytogenetic Locus: 3-exon gene on chromosome 12q21.31 positioned 8.5 kb upstream of MYF5 in a tandem head-to-tail cluster, sharing overlapping cis-regulatory elements so that early MYF6 knockout alleles inadvertently disrupted adjacent MYF5 transcription.
Cellular & Tissue Expression Profile: Expressed in a biphasic developmental wave: transiently in embryonic somites alongside MYF5, and then massively up-regulated after birth to become the single most abundant myogenic regulatory factor mRNA and protein in mature, innervated adult skeletal muscle fibers.
Molecular Function & Pathways
Biochemical & Physiological Mechanism: Maintains adult myofiber identity and neuromuscular junction gene expression while acting as an unexpected negative regulator of adult muscle growth: in mature innervated myofibers, MYF6 recruits HDAC4 corepressor complexes to restrain MEF2 transcriptional activity, whereas experimental RNAi knockdown or denervation-induced loss of MYF6 derepresses MEF2 target genes and triggers significant adult myofiber hypertrophy even in the absence of myostatin blockade.
Clinical & Therapeutic Significance
Human Genetic Variants & Disease Phenotypes: Rare coding variants in MYF6 have been reported as genetic modifiers increasing clinical severity in Becker muscular dystrophy (DMD) and in centronuclear myopathy pedigrees.
Therapeutic & Clinical Pharmacology: Completes the classic vertebrate quartet of basic helix-loop-helix Myogenic Regulatory Factors (MYF5, MYOD1, MYOG, and MYF6/MRF4), with adult MYF6-MEF2 signaling providing an independent transcriptional lever for counteracting sarcopenia and disuse atrophy.