DYSTROPHIN-POSITIVE MUSCLE-FIBERS FOLLOWING C2 MYOBLAST TRANSPLANTATION INTO MDX NUDE-MICE

To determine when and how the dystrophin-positive muscle fibers are fo rmed after myoblast transplantation into dystrophin-negative muscles, the tibialis anterior (TA) muscle from mdx nude mouse was chronologica lly examined after C2 myoblast transplantation by immunohistochemical and glucose 6-phosphate isomerase (GPI) isoenzyme analyses. The host T A muscle transplanted with C2 myoblasts became necrotic with accumulat ion of basic fibroblast growth factor in the necrotic areas. This may stimulate concomitant proliferation of the host satellite cells and C2 myoblasts. Small dystrophin-positive muscle fibers appeared in the ne crotic areas 3 days after transplantation. This TA muscle contained tw o different kinds of homodimer GPI isoenzymes but did not contain the heterodimer, suggesting rare fusion of host and donor cells. The dystr ophin-positive muscle fibers in the necrotic areas rapidly increased i n number and in size by 7 days, but they were smaller than the origina l host muscle fibers. They had central nuclei, indicating that they we re regenerating fibers. The presence of heterodimer GPT isoenzyme in t hese muscles indicated that the regenerating fibers were mosaic host/d onor muscle fibers. The dystrophin-positive muscle fibers are probably formed first by fusion of donor cells with each other and then later by the fusion of host satellite and donor cells.