Two Novel Zebrafish Mutants Reveal Genes Necessary for Neuronal and Muscle Function

The peripheral nerve is a complex structure composed of several cell types that must interact and communicate to form a healthy nerve. The perineurium, which encloses multiple axon-Schwann cell bundles, is necessary for nerve protection and structural support, but many questions remain about its development. To that end, an ENU mutagenesis screen was performed in zebrafish using the transgene Tg(nkx2.2a:megfp), a marker of perineurial glia. Two zebrafish mutants were identified in this screen: failure to launch (ftl)vu268 and runaway (ray)vu267. These mutants have contrasting glial phenotypes: in ftlvu268 embryos, glia fail to migrate out of the spinal cord, and in rayvu267 embryos, the glia migrate ectopically and exhibit a highly branched morphology. These mutants were further characterized and mapping of their mutations was attempted using several techniques, including bulk segregant analysis, whole genome sequencing (WGS) and allele-specific PCR.
For ftlvu268, the candidate list was narrowed to a handful of genes, but the gene was not identified. However, the newest zebrafish genome casts these previous efforts into doubt. Nevertheless, in these mutants we were still able to characterize severe glial defects, including fewer Schwann cells and oligodendrocytes and the absence of myelination in mutant larvae.
In rayvu267 embryos, the mutation was found to be located within the dystrophin gene on chromosome 1. Interestingly, we characterized many novel nervous system phenotypes in these mutants as well as in sapje-likecl100 mutants, which have a different mutation in dystrophin. This study illustrates the importance of a healthy, functioning nervous system in muscle function of DMD patients. This dissertation reviews novel and unexpected aspects of the development of perineurial glia, and also provides a foundation for future work.