An Axon-Pathfinding Mechanism Preserves Epithelial Tissue Integrity

Dividing cells often move apically within epithelial tissue layers, likely to escape the spatial confinement of their neighbors. Because of this movement, daughter cells may be born displaced from the tissue layer. Reintegration of these displaced cells helps support tissue growth and maintain tissue architecture. In the Drosophila follicular epithelium, reintegration relies on the immunoglobulin-superfamily cell-adhesion molecules (IgCAMs) Neuroglian and Fasciclin 2, which line cell-cell borders1. These molecules have been described in epithelia, but are well-studied for their roles in neural development2-8. We show here that reintegration works in the same way as IgCAM-mediated axon growth and pathfinding; it relies not only on extracellular adhesion but also mechanical coupling between IgCAMs and the lateral Spectrin-Based Membrane Skeleton. Our work indicates that reintegration is mediated by a distinct epithelial cell-cell junction that is compositionally and functionally equivalent to junctions made between axons.