Fig. 5. Expression of MT1-MMP and MMP-2 in regenerating skeletal muscle. (A) The tibialis anterior (TA) muscles of 2-3 month old mice were injured by injecting cardiotoxin, and regeneration was monitored by histology with HE staining. Arrowheads indicate that regenerating myofibers having centrally located nuclei at day 4. Bar, 20,000 µm. (B) MMP expression levels in the regenerating muscle tissues. MMP-2 expression was monitored by gelatin zymography (upper panel). Closed and open arrowheads on the right indicate active- and pro-form of MMP-2, respectively. Western blot in the lower panel shows the expression profile of MT1-MMP. Open arrowhead indicates active MT1-MMP and closed arrowhead shows an autolytically degraded fragment.