Fig. 1: Basic characterization of the mouse strains.

a Top: Nebulin localizes to the thin filament of the skeletal muscle sarcomere. Bottom: The structure of mouse nebulin with the S6366I site indicated (in super-repeat 22, orange) and the ΔExon55 site (in super-repeat 9, pink). A mouse was created with compound heterozygous Neb mutations: one missense mutation in exon 106 (Neb^S6366I) and one in-frame deletion of exon 55 (Neb^Δexon55), the Neb ^{S6366I/Δexon55}, or Compound-Het for short. b When breeding Het Neb^S6366I parents, genotypes of offspring follow Mendelian genetic ratios (top) and when breeding Het Neb^S6366I with Het Neb^Δexon55 parents (bottom), offspring also closely follows Mendelian genetics. c Body weight vs. days-of-life. Gompers non-linear least squares fit with as null hypothesis that one curve fits all data sets. Test (Sum-of-squares F-test) reveals that the null hypothesis is rejected (p ≤ 0.0001; F (DFn, DFd): 63 (3,341)). (Results of male mice are shown with similar results found for female mice (not shown).) d Tibia length is reduced in Compound-Het and Neb^S6366I homozygous 4 months old male mice. An ordinary one-way ANOVA without matching or paring was performed with a posthoc multiple testing comparison with multiple testing correction (Sidak). *p = 0.02; **p = 0.008. e Grip strength in Compound-Het and Neb^S6366I mice, 1, 4 and 10 mo of age. A two-way ANOVA (no matching) reveals a significant effect of age and genotype on grip strength but without interaction. A posthoc multiple testing comparison with multiple testing correction (Dunnett) reveals a significant grip strength reduction at all 3 ages in Compound-Het mice and a significant reduction in 10 mo old Neb^S6366I mice. **p < 0.01; ****p < 0.0001. f In 3 mo old male mice (left) Compound-Het mice have a 35% decreased maximal lower limb force and Neb^S6366I Hom have a 7% reduction. In 10 mo old male mice (middle) the reduction is 37% and 18% and in 10 mo old female mice (right) the reduction is 37% and 18%. Non-linear least squares fit to Hill curve with as null hypothesis that one curve fits all data sets. Test (Sum-of-squares F-test) reveals that the null hypothesis is rejected in each panel (****p ≤ 0.0001; F (DFn, DFd): 104.2 (8,208)). g Relative force-frequency relation (same data as in f, left) shows a left shift for both the Compound-Het and Neb^S6366I Hom mice with increased relative force at the shown frequencies of 40 and 60 Hz (One-way ANOVA without matching or paring performed with a posthoc multiple testing comparison with multiple testing correction (Sidak). ****p < 0.0001. Inset: decreased frequency for ½ maximal force in Compound-Het mice. Ordinary one-way ANOVA without matching or paring. A posthoc multiple testing comparison with multiple testing correction (Sidak). *p = 0.02. Number of mice in b 291 (top) and 668 (bottom); c, d: WT: 21, Compound-Het: 18, and NebS6366I Hom: 16; e 1 mo 19, 14, 12; 4 mo: 22, 18, 12; 10 mo 14, 6, 10. f left and g: WT: 9, Compound-Het: 7, and Neb^S6366I Hom: 6; f middle: WT: 6, Compound-Het: 2, and NebS6366I Hom: 6; f right WT: 6, Compound-Het: 4, and Neb^S6366I Hom: 3. g Inset 9 WT mice, 6 Compound-Het mice and 7 Neb^S6366I Hom mice. Bar values are mean ± SEM. Source data are provided as a Source Data file.