Required for myofiber maturation. Expressed in muscle fibers in a regular striated pattern (at protein level). At 24 hpf, expressed in the somites and several regions of the brain, including the midbrain roof (tectum). At 2 dpf, morphants are morphologically normal but show pericardial edema and tail curvature. They exhibit near complete paralysis at embryonic and larval stages, producing extremely low levels of spontaneous coiling movements and a greatly diminished touch response. They show a severe disorganization of the contractile apparatus in muscle fibers. Sarcomeric structures in mutants are almost entirely absent and only rare triads are observed. Belongs to the protein-tyrosine phosphatase family. Non-receptor class dual specificity subfamily. Ser-234 is present instead of the conserved Cys which is expected to be an active site residue suggesting that this protein has lost its phosphatase activity.