title: Analysis of protein dynamics within the septate junction reveals a highly stable core protein complex that does not include the basolateral polarity protein Discs large.
abstract: Barrier junctions prevent pathogen invasion and restrict paracellular leakage across epithelial sheets. To understand how one barrier junction, the septate junction (SJ), is regulated in vivo, we used fluorescence recovery after photobleaching (FRAP) to examine SJ protein dynamics in Drosophila. Most SJ-associated proteins, including Coracle, Neurexin IV and Nervana 2, displayed similar, extremely immobile kinetics. Loss of any of these components resulted in dramatically increased mobility of all others, suggesting that they form a single, highly interdependent core complex. Immobilization of SJ core components coincided with formation of the morphological SJ but occurred after their known role in maintaining epithelial polarity, suggesting that these functions are independent. In striking contrast to the core components, the tumor suppressor protein Discs large was much more mobile and its loss did not affect mobility of core SJ proteins, suggesting that it is not a member of this complex, even though it colocalizes with the SJ. Similarly, disruption of endocytosis affected localization of SJ core components, but did not affect their mobility. These results indicate that formation of a stable SJ core complex is separable from its proper subcellular localization, and provide new insights into the complex processes that regulate epithelial polarity and assembly of the SJ.
authors.affiliation: Department of Molecular Genetics and Cell Biology, University of Chicago, 920 E. 58th Street, CLSC 925B, Chicago, IL 60637, USA.
authors.forename: Kenzi
authors.initials: K
authors.lastname: Oshima
authors.forename: Richard G
authors.initials: RG
authors.lastname: Fehon
mesh_terms: D000818:Animals; D015816:Cell Adhesion Molecules, Neuronal / Q000235:genetics / Q000378:metabolism; D002460:Cell Line; D016764:Cell Polarity; D004330:Drosophila; D029721:Drosophila Proteins / Q000235:genetics / Q000378:metabolism*; D004625:Embryo, Nonmammalian; D004847:Epithelial Cells / Q000648:ultrastructure; D036681:Fluorescence Recovery After Photobleaching; D006023:Glycoproteins / Q000235:genetics / Q000378:metabolism; D007365:Intercellular Junctions / Q000378:metabolism* / Q000648:ultrastructure; D007814:Larva; D008565:Membrane Proteins / Q000235:genetics / Q000378:metabolism; D046912:Multiprotein Complexes / Q000378:metabolism*; D009154:Mutation / Q000235:genetics; D009419:Nerve Tissue Proteins / Q000235:genetics / Q000378:metabolism; D011485:Protein Binding; D021381:Protein Transport; D019076:Transgenes / Q000235:genetics; D025521:Tumor Suppressor Proteins / Q000378:metabolism*
chemical_list: D015816:Cell Adhesion Molecules, Neuronal; D029721:Drosophila Proteins; D006023:Glycoproteins; D008565:Membrane Proteins; D046912:Multiprotein Complexes; D009419:Nerve Tissue Proteins; C094061:Nrv2 protein, Drosophila; C491321:Nrx protein, Drosophila; D025521:Tumor Suppressor Proteins; C442474:cora protein, Drosophila; C070350:dlg1 protein, Drosophila