Despite the importance of glial cells in the nervous system, many questions remain unanswered about the mechanisms that govern their development and function. To discover genes with essential functions in glia, we have conducted three different genetic screens to find new mutations that affect the development of microglia and myelinated axons. In the first of these, we analyzed more than 1850 clutches of F3 larvae to identify mutations with specific defects in the expression of mbp mRNA. This screen identified 13 mutations in 10 genes that disrupted mbp expression in the CNS, in the PNS, or in both (Pogoda et al. 2006, Developmental Biology 298: 118-131). Our second, smaller screen expanded the scope of phenotypes examined by assaying sodium channel (NaCh) expression at nodes of Ranvier in myelinated axons (Voas et al. 2007, Current Biology 17: 562-568). In a third genetic screen, we identified mutations that disrupt the ability of microglia to engulf the dye neutral red (Shiau et al. 2013, Cell Reports 5: 1342-1352). None of these screens was pursued to saturation, so continued screening will yield mutations in genes that have not yet been defined. Most of the mutants have normal morphology, suggesting that the mutated genes have relatively specific functions in the development of glial cells or the associated neurons. Phenotypic studies indicate that the mutated genes act in many different processes, including glial fate specification, axon outgrowth, glial migration, organization of the nodes of Ranvier, lysosomal function, and control of inflammation. In addition, several of the genes have been associated with human disease, indicating that analysis of these zebrafish mutants will yield important insights into diseases that disrupt glial development and function.
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