DUX4c, an FSHD candidate gene, interferes with myogenic regulators and abolishes myoblast differentiation

Facioscapulohumeral muscular dystrophy (FSHD) is an autosomal dominant neuromuscular disease. It maps to the D4Z4 repeat array at 4q35, and correlates with a repeat contraction which derepresses transcription of local genes. Which, if any, of these genes is pathogenic to muscle, and through what molecular mechanism is unknown. The present study investigates the function of one candidate gene, DUX4c, encoded by a truncated inverted D4Z4 element located 42 kb proximal to the D4Z4 repeats. Using a gain of function approach we tested DUX4c for toxicity and effects on differentiation in C2C12 myoblasts. DUX4c-expressing myoblasts appear morphologically normal but have reduced expression of myogenic regulators, including MyoD and Myf5. Consistent with this, DUX4c-expressing myoblasts are unable to differentiate into myotubes. Furthermore, overexpression of Myf5 or MyoD rescued myoblast differentiation, suggesting that reductions in expression of these regulators are the relevant DUX4c-induced physiological changes that inhibit differentiation. Our results suggest that upregulation of DUX4c can have a deleterious effect on muscle homeostasis and regeneration, and point to a possible role for DUX4c in the pathology of FSHD.