In zebrafish, the recessive lethal mutation sapje causes progressive degeneration of skeletal muscles, reminiscent of human muscular dystrophies. Bassett and co-workers show that the sapje mutation disrupts the zebrafish orthologue of the human Duchenne muscular dystrophy (DMD) gene (see ). In a detailed study of the structure of the muscles throughout embryonic development, the researchers report that the progressive muscle degeneration in the mutant fish is caused by the separation of somitic fibres from their attachment points on tendon-like sheets of extracellular matrix, called myosepta. These attachment points resemble mammalian myomuscular and myotendinous junctions. However, although structural deficits of myotendinous junctions have been seen in mouse models of Duchenne muscular dystrophy,dystrophin has not previously been implicated in the maintenance of either structure. Thus, say the researchers, the sapje mutant may be a good model for a hitherto unsuspected pathological mechanism in muscular dystrophies.
