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Rap, Axon, Drosophila


The development of the wild type Drosophila compound eye involves stereotypical targeting of photoreceptor axons to the specific layers of the optic ganglion, medulla and lamina, in the third instar larvae. To test the hypothesis that ubiquitin ligases play an important role during retinal axon targeting we have examined the patterns of axon targeting in the developing eye of the retina aberrant in pattern (rap/fzr) mutants. Rap/Fzr is a homolog of mammalian Cdh1, an activator of anaphase promoting complex (APC), an E3 ubiquitin ligase. Previous work has shown that Rap/Fzr is required in cell cycle regulation, glia differentiation and pattern formation during eye development. Results from our experiments show that Rap/Fzr is required for proper retinal axon targeting in the developing eye. Our studies using ro-tau-lacZ show that the R2-R5 axons fail to stop in the lamina and mis-target to the medulla levels. Mosaic analyses experiments using FLP-FRT and GAL4-UAS techniques show that Rap/Fzr functions in a cell autonomous manner. To test for possible role of other signaling molecules and interactions with Rap/Fzr, we have examined rap phenotypes in double mutant combinations with Loco, Liprin-α, and RasV12 mutants. Our studies suggest that Rap/Fzr is required for proper axon targeting during Drosophila visual system development. These results are consistent with other mammalian studies reporting a role of Cdh1 in axon growth and targeting and provides further insights into neuronal functions of the ubiquitin ligase APCCdh1.

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