SummarySeptate 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.

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A nuclear polyhedrosis virus (NPV) (Baculoviridae)-based gene expression system was improved by DNA recombination. The BmN cell line established from Bombyx mori and the Sf21 cell line established from Spodopterafrugiperda are non-permissive for Autographa californica multicapsid NPV (AcMNPV) and B. mori NPV (BmNPV) replication, respectively. After cotransfection of AcMNPV DNA and BamHI-digested BmNPV DNA into Sf21 cells, progeny viruses were isolated by plaque purification on BmN cell monolayers and the host specificity of one viral isolate was analysed. The virus had a wider host range, and replicated and produced polyhedra in Sf21 cells, BmN cells and larvae of the silkworm, B. morL DNA restriction endonuclease analysis showed that the isolate was a hybrid of AcMNPV and BmNPV. Using