Insights into intracellular events of the planar cell polarity pathway : a new paradigm for the mechanisms of dishevelleds and dishevelled dependent effector proteins
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Dishevelled (Dvl) proteins are key transducers of Wnt signaling and are encoded by members of a multi-gene family in vertebrates. We report here divergent, tissue-specific expression patterns for all three Dvl genes in Xenopus embryos, which contrast dramatically with their expression in the mouse. Moreover, we find that the expression patterns of Dvl genes in the chick diverge significantly from those of Xenopus. In addition, in hemichordates, one of the outgroups to chordates, we find that the one Dvl gene is dynamically expressed in a tissue-specific manner. Using knockdowns, we find that Dvl1 and Dvl2 are required for early neural crest specification and for somite segmentation. Most strikingly, we report a novel role for Dvl3 in the maintenance of differentiated muscle and the development of the Xenopus sclerotome. Together, these data demonstrate that that the expression patterns and developmental functions of specific Dvl genes have diverged significantly during chordate evolution. The planar cell polarity (PCP) signaling pathway is essential for embryonic development because it governs diverse cellular behaviors, and the "core PCP" proteins, such as Dishevelled and Frizzled, have been extensively characterized. By contrast, the "PCP effector" proteins, such as Intu and Fuz, remain largely unstudied. These proteins are essential for PCP signaling, but they have never been investigated in a mammal and their cell biological activities remain entirely unknown. We report here that Fuz mutant mice display neural tube defects, polydactyly, and skeletal dysmorphologies that stem from defective ciliogenesis. Using bioinformatics and imaging of an in vivo mucociliary epithelium, we establish a central role for Fuz in membrane trafficking, showing that Fuz is essential for apical trafficking of ciliogenesis factors in ciliated cells and also for exocytosis in secretory cells. We identify a novel, Rab-related small GTPase as an interaction partner for Fuz, and this GTPase also is essential for ciliogenesis and secretion. These results are significant because they provide novel insights into the mechanisms by which developmental regulatory systems like PCP signaling interface with fundamental cellular systems such as the vesicle trafficking machinery.