Non-occluding Functions of Septate Junction Proteins in Signaling Regulation and Cell Polarity during Epithelial Development

Occluding junctions are essential for epithelial tissue integrity and barrier function but also exert non-occluding roles. Here we identify a several crucial function of the invertebrate occluding junction components Coracle, Nervana 2, Neurexin-IV, and Kune-kune in regulating cell polarity during follicle epithelium development. We show that the morphogenesis of the follicular stalk is an actin-driven process that requires intact apical-basal cell polarity, which is controlled by septate junction components. Occluding junction components further regulate signaling pathways in a cell-type specific manner. In undifferentiated stem cells and immediate daughters, septate junction components promote effective Wnt signaling to control proliferation, while they limit Jak-STAT signaling activity induced by polar cells. Together, our data emphasize the multiple roles of occluding junction components independent of their classical role in forming the paracellular barrier.