Figure 4.
Z-discs are disorganized, thick filaments are absent, and the sarcoplasmic reticulum is dilated in runx1 mutant denervated myofibers. (a,b) In denervated (14-d) muscle of control runx1f/f mice, the Z-discs (arrow) are aligned, the actin-only I-bands (I) and actin + myosin A-bands (A) are readily apparent, and the sarcoplasmic reticulum (SR) and transverse-tubules (T) are situated between the myofibrils. (c,d) In denervated (14-d) MCK::cre; runx1f/f myofibers, the Z-discs are misaligned and fragmented (arrow in c), distinct I- and A-bands are not discernible, and the SR is severely dilated and extends from the Z-disc into the myofibril. Myofibers that had been denervated for 1 wk were similarly, though less severely affected. Bars: a,c, 0.5 μm; b,d, 0.12 μm.