Division of Cell Biology, Department of Physiology and Cell Biology, Graduate School of Medicine, Kobe University, Kobe 650-0017, Japan.
J Cell Sci. 2012 Apr 15;125(Pt 8):1980-90. doi: 10.1242/jcs.096800. Epub 2012 Feb 10.
Septate junctions (SJs) are the membrane specializations observed between epithelial cells in invertebrates. SJs play a crucial role in epithelial barrier function by restricting the 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 identification of pSJ-related proteins, the molecular constituents of sSJs are mostly unknown. Here, we report the discovery of a new 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.
隔膜连接（SJ）是存在于无脊椎动物上皮细胞之间的膜特化结构。SJ 通过限制溶质通过细胞间隙的自由扩散，在上皮屏障功能中起着至关重要的作用。在节肢动物物种中，已经描述了两种形态上不同类型的 SJ：褶皱隔膜连接（pSJ）和光滑隔膜连接（sSJ），它们分别存在于外胚层和内胚层上皮中。与最近鉴定的 pSJ 相关蛋白不同，sSJ 的分子组成大部分是未知的。在这里，我们报告了一种新的 sSJ 特异性膜蛋白的发现，命名为“蛇皮”（Ssk）。Ssk 在果蝇中肠和马氏管的 sSJ 中高度富集。果蝇中 Ssk 表达缺失在胚胎期是致命的，导致 sSJ 形成缺陷，伴随中肠上皮细胞形态异常。我们还表明，ssk 敲低幼虫的中肠对荧光示踪剂的屏障功能受损。这些结果表明 Ssk 是果蝇肠道屏障功能所必需的。
