The number of fibers expressing MyHC-β is dramatically increased in Sox6 KO skeletal muscle. A. Cross-sections of E18.5 lower hindlimb muscle (TA-EDL region) from control (Sox6f/f) and Sox6KO (Sox6f/f; Myf5-Cre) were stained with DAPI (blue) or specific antibodies for MyHC-β (green) or Sox6 (red). x400 magnification. B. P7 (7 day old) hindlimb muscle processed for DAPI, Sox6 and MyHC-β immune-staining.* indicates myotubes that are negative for both MyHC-β and Sox6 staining in control muscle (see text for discussion). x400 magnification. C. Four month old adult TA-EDL muscle. A control muscle section stained with DAPI or secondary antibodies (a mixture of both anti-mouse and anti-rabbit) only was also shown. ×200 magnification.