Varicose: a MAGUK required for the maturation and function of Drosophila septate junctions

Varicose localizes to pleated septate junctions (pSJs) of all embryonic, ectodermally-derived epithelia and peripheral glia. In vari mutants, essential SJ proteins NeurexinIV and FasciclinIII are mislocalized basally and epithelia develop a leaky paracellular seal. In addition, vari mutants display irregular tracheal tube diameters and have reduced lumenal protein accumulation, suggesting involvement in tracheal morphogenesis. We found that Vari is distributed in the cytoplasm of the optic lobe neuroepithelium, as well as in a subset of neuroblasts and differentiated neurons of the nervous system. We reduced vari function during the development of adult epithelia with a partial rescue, RNA interference and generation of genetically mosaic tissue. All three approaches demonstrate that vari is required for the patterning and morphogenesis of adult epithelial hairs and bristles.Varicose is involved in scaffold assembly at the SJ and has a role in patterning and morphogenesis of adult epithelia.The assembly of cellular junctions is pivotal for metazoans to maintain a homeostatic environment. Through these junctions, cells are able to communicate, synchronize function, and regulate the paracellular flow of molecules [1-3]. Epithelial cells are polarized along an apico-basal axis where the apical surface faces the exterior or lumen and the basal surface communicates with the extracellular matrix [4]. In vertebrates, several epithelial intercellular junctions exist, the two most widely studied being tight junctions (TJs) and adherens junctions (AJs) [5,6]. Invertebrate species, although lacking tight junctions possess the functionally analogous septate junction (SJ) [7]. Despite a difference in lateral membrane location, TJs (apical to AJs) and SJs (basal to AJs) both form an intercellular barrier to regulate the transepithelial diffusion of solutes [8].Ultrastructure and freeze-fracture analysis of cell junctions reveal that SJs maintain a fixed distance between epithelia