Rescue of Photoreceptor Degeneration in Rhodopsin-Null Drosophila Mutants by Activated Rac1

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Abstract
Rhodopsin is essential for photoreceptor morphogenesis; photoreceptors lacking rhodopsin degenerate in humans, mice, andDrosophila. Here we report that transgenic expression of a dominant-active Drosophila Rho guanosine triphosphatase, Drac1, rescued photoreceptor morphogenesis in rhodopsin-null mutants; expression of dominant-negative Drac1 resulted in a phenotype similar to that seen in rhodopsin-null mutants. Drac1 was localized in a specialization of the photoreceptor cortical actin cytoskeleton, which was lost in rhodopsin-null mutants. Thus, rhodopsin appears to organize the actin cytoskeleton through Drac1, contributing a structural support essential for photoreceptor morphogenesis.