Isolated myofiber immunostaining and electron microscopy (EM) in skeletal fast muscle fibers in srpk3 − / − ; ttn.1 +/ − larvae at 5 dpf. Isolated myofiber immunostaining showed that titin expression is largely reduced in the double mutant ( srpk3 −/− ; ttn.1 +/− ; l , p ) but not in the single heterozygous ttn.1 mutant ( srpk3 +/+ ; ttn.1 +/− ; j , n ) or the srpk3- null ( srpk3 −/− ; ttn.1 +/+ ; k , o ). EM showed that srpk3 -null zebrafish ( srpk3 −/− ; ttn.1 +/+ ; s ) had well-defined sarcomeres, with mildly disorganized myofibrils. The double-mutant fish ( srpk3 −/− ; ttn.1 +/− ) displayed pronounced disruption of the sarcomere structure. White scale bars are 25 µm. Black scale bar is 500 nm. Representative images from >15 pooled fish per genotype.
