Figure 4

Increased muscular workload causes skeletal muscle disruption in later developmental stages of nexn knockout embryos. (a) Brightfield and birefringence images do not reveal phenotypical differences between nexn^+/+ and nexn^−/− embryos at 72 hpf. (b) Percentage of embryos showing phenotypical abnormalities does not differ between nexn^+/+ and nexn^−/− embryos at 48, 72 or 120 hpf (N = 3, mean ± SD, 48 hpf: p > 0.9999, 72 hpf: p = 0.8000, 120 hpf: p > 0.9999 using Mann–Whitney test). (c) Densitometric quantification of birefringence signals of nexn^−/− and nexn^+/+ embryos after stress reveals significant differences at 120 (N = 3, n = 15, mean ± SD, p < 0.0046 using two-tailed t-test) but not 48 or 72 hpf (N = 3, n = 14/15, mean ± SD, 48 hpf: p = 0.6516, 72 hpf: p = 0.2193 using two-tailed t-test). (d) Immunostaining of nexn^+/+ and nexn^−/− embryos after stress against Titin does not show altered muscle fibers at 48 and 72 hpf but severe muscle disruption in cranial regions (location shown in schematic illustration; created with biorender.com) at 120 hpf. Scale bar (1 µm) refers to all images. ns not significant, **p < 0.01. Exact values (mean ± SD) are shown in Supplementary Table 1.