Effect of a mybphb deletion allele on MyBP isoform accumulation and morphology in 5 dpf larval tails. (A) Quantitative LCMS of tails from heterozygous (mybphb^+/−) and homozygous (mybphb^−/−) larvae show reduction and ablation of Mybphb, respectively, compared with wildtype. Statistics were calculated using a two-tailed Student’s t test. Magenta or cyan * denote P < 0.05 between bars of the corresponding colors. In each case, Mybpc2b accumulation increases slightly, but does not fully compensate for the loss of Mybphb. (B–D)Mybphb^−/− larvae display no gross morphological phenotype or change in relative or absolute fast-twitch or slow-twitch muscle cross-section area. (E–H) TEM images of longitudinal (E and G) and transverse (F and H) ∼80 nm sections of 5 dpf fast-twitch muscle cells revealed no deviations from normal muscle ultrastructure in the absence of Mybphb. Statistics were calculated using a two-tailed Student’s t test. ns denotes P > 0.05. Data are presented as Means ± 1 SD.