RyR-mediated muscle contractions are required for slow fiber maturation. (A-I) Slow fibers were visualized with F59 antibody at 20 and 24 hpf and with the slow fiber-specific S58 antibody at 48 hpf. Slow fibers, which are initially wavy, mature and align with respect to each other as wild-type embryos develop. In ryr1b mutant embryos, maturation is delayed; in paralyzed triple mutants, fiber maturation is arrested. (J) Sample image indicating how slow muscle fiber (yellow) and A-P somite (magenta) lengths were determined using ImageJ. (K) Sample image of sarcomere banding indicating how sarcomere A-P lengths (white bracket) were determined. (L) Quantification of slow fiber:somite length ratios. (M) Quantification of sarcomere lengths of slow muscle fibers. One-way ANOVA was used to determine statistical relationships at each developmental time point with Tukey's multiple comparisons test used to adjust P-values. To determine fiber length or sarcomere length, five fibers were examined in each of five different embryos for each condition. ns, not significant.
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