A novel smooth septate junction-associated membrane protein, Snakeskin, is required for intestinal barrier function inDrosophila

Abstract

Septate junctions (SJs) are the membrane specializations observed between epithelial cells in invertebrates. SJs play a crucial role in epithelial barrier function by restricting free diffusion of solutes through the intercellular space. In arthropod species, two morphologically different types of SJs have been described: pleated septate junctions (pSJs) and smooth septate junctions (sSJs), which are specific to ectodermal and endodermal epithelia, respectively. In contrast to the recent understanding of pSJ-related proteins, the molecular constituents of sSJs are mostly unknown. Here we report a novel sSJ-specific membrane protein, designated ‘Snakeskin’ (Ssk). Ssk is highly concentrated in sSJs in the Drosophila midgut and Malpighian tubules. Lack of Ssk expression is embryonically lethal in Drosophila and results in defective sSJ formation accompanied by abnormal morphology of midgut epithelial cells. We also show that the barrier function of the midgut to a fluorescent tracer is impaired in Ssk-knockdown larvae. These results suggest that Ssk is required for the intestinal barrier function in Drosophila.