Expression and subcellular localization of dystrophin in skeletal, cardiac and smooth muscles during the human development.

Dystrophin, the product of the DMD gene, is present in all muscle types in normal individuals. Its function has yet to be elucidated, but its absence or the presence of a truncated version of the protein is responsible for the appearance of Duchenne and Becker muscular dystrophies. Using monoclonal antibodies raised against distinct regions of the dystrophin protein, we have examined its expression and subcellular distribution during the human development in skeletal and smooth muscles. We show that both dystrophin expression and its association to the plasma membrane take place earlier in cardiac and smooth muscles (8 weeks of gestation) than in skeletal muscle. In skeletal muscle, dystrophin is first detected in the cytoplasm, and progressively localizes to the plasma membrane from 10 weeks onwards. Since we have obtained marked differences in staining when using antibodies against either a central region of the protein or the C-terminal part, we suggest that different fetal and adult dystrophin isoforms are expressed, probably differing in their C-terminal domain. These findings are discussed in the context of the pathology of Duchenne muscular dystrophy.