Figure 8.

Muscle fiber nuclei are enriched in the synaptic region of Macf1-conditional mutant mice. (A) Myonuclei accumulate in the subsynaptic region of muscle from control and Macf1 mutant mice. The total number of subsynaptic myonuclei is reduced by 18% in Macf1 muscle-conditional mutant mice at P180. The number of subsynaptic nuclei, normalized to synaptic size, is increased by 22% in Macf1 mutant mice. The number of nuclei in the perisynaptic region is increased by twofold. Synaptic sites were marked by staining for AChRs (red), and nuclei were stained with Hoechst 33342 (cyan). The mean ± SEM values from three mice (30 synapses per mouse) are shown (**, P < 0.005; ***, P < 0.0005). A long arrow indicates a subsynaptic nucleus, an arrowhead indicates a perisynaptic nucleus, which is adjacent to the synaptic site, and a short arrow indicates a nonsynaptic nucleus. Bar, 10 µm. (B) We distinguished between nuclei of perisynaptic cells, including Schwann cells, and myofiber nuclei by optical sectioning of muscle tissue stained for nuclei (cyan), AChRs (red) and Synapsin (green); we only counted nuclei within the myofiber. Bar, 5 µm.