Developmental studies of dystrophin-positive fibers in mdx, and DRP localization.

Dystrophin positive fibers (DPFs) were observed in about 1% of the total muscle fibers in 1-year-old mice. Some of these fibers were found to have positive staining with all six antibodies, while others showed a negative reaction with specific antibodies. These results suggest that the most likely mechanism giving rise to these DPFs is a second site mutation which prepares in-frame deletion. A study of the frequency of DPF during development showed single and scattered DPFs in younger mice, which gradually increased in number and began to form small groups with age. DRP was observed constantly on the neuromuscular junctions in both control and mdx muscle, and surface membrane of immature muscle fibers such as regenerating fibers in mdx and newborn muscle during 2 weeks of age in control and mdx.