Basal lamina and superfast myosin expression in regenerating cat jaw muscle.

We investigated the possible role of extracellular matrix in specifying the expression of superfast myosin during cat jaw muscle regeneration. Equal proportions of muscle tissue from jaw and limb were minced together after killing cellular elements from one source. We allowed the mince to regenerate in the bed of a fast limb muscle. Regenerates were analyzed immunocytochemically at 71 to 294 days after operation. Fibers in control regenerates containing live cells from both sources expressed fast, superfast or slow myosins, or a mixture of these myosins. In regenerates containing only one type of live cells, we detected only myosins appropriate to the live cells. Our results suggest that during regeneration the original extracellular matrix of jaw-closing or limb muscle is unable to specify the expression of superfast or fast myosins, respectively; they point to the cellular elements, probably the satellite cells, as determinants of muscle specificity during regeneration.