GENES-CONTROLLING AND MEDIATING LOCOMOTION BEHAVIOR OF THE ZEBRAFISH EMBRYO AND LARVA

Zebrafish embryos and larvae have stage-specific patterns of motility or locomotion, Two embryonic structures accomplish this behavior: the central nervous system (CNS) and skeletal muscles. To identify genes t hat are functionally involved in mediating and controlling different p atterns of embryonic and larval motility, we included a simple touch r esponse test in our zebrafish large-scale genetic screen, In total we identified 166 mutants with specific defects in embryonic motility. Th ese mutants fall into 14 phenotypically distinct groups comprising at least 48 genes, Here we describe the various phenotypic groups includi ng mutants with no or reduced motility, mechanosensory defective mutan ts, 'spastic' mutants, circling mutants and motor circuit defective mu tants, In 63 mutants, defining 18 genes, striation of semitic muscles is reduced, Phenotypic analysis provides evidence that these 18 genes have distinct and consecutive functions during semitic muscle developm ent. The genes sloth (slo) and frozen (fro) already act during myoblas t differentiation, while 13 genes appear to function later, in the for mation of myofibers and the organization of sarcomeres, Mutations in f our other genes result in muscle-specific degeneration,103 mutations, defining at least 30 genes, cause no obvious defects in muscle formati on and may instead affect neuronal development. Analysis of the behavi oral defects suggests that these genes participate in the diverse loco motion patterns observed, such as touch response, rhythmic tail moveme nts, equilibrium control, or that they simply confer general motility to the animal, In some of these mutants specific defects in the develo ping nervous system are detected, Mutations in two genes, nevermind (n ev) and macho (mao), affect axonal projection in the optic tectum, whe reas axon formation and elongation of motorneurons are disrupted by mu tations in the diwanka (diw) and the unplugged (unp) genes.