swap70 promotes neural precursor cell cycle exit and oligodendrocyte formation.

Multipotent neural precursors produce oligodendrocyte lineage cells, which then migrate throughout the central nervous system and extend multiple, long membrane processes to wrap and myelinate axons. These dynamic cellular behaviors imply dynamic regulation of the cytoskeleton. In a previous microarray screen for new oligodendrocyte genes we identified swap70, which encodes a protein with domains that predict numerous signaling activities. Because mouse Swap70 can promote cell motility by functioning as a guanine nucleotide exchange factor for Rac1, we hypothesized that zebrafish Swap70 promotes oligodendrocyte progenitor cell (OPC) motility and axon wrapping. To test this we investigated Swap70 localization in OPCs and differentiating oligodendrocytes and we performed a series of gain and loss of function experiments. Our tests of gene function did not provide evidence that Swap70 regulates oligodendrocyte lineage cell behavior. Instead, we found that swap70 deficient larvae had excess neural precursors and a deficit of OPCs. Cells associated with neural proliferative zones express swap70. Therefore, our data reveal a potential new role for Swap70 in regulating transition of dividing neural precursors to specified OPCs.

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