A Dystroglycan-Laminin-Integrin axis controls cell basal geometry remodeling in the developing Drosophila retina

Cell shape remodeling is a principal driver of epithelial tissue morphogenesis. While progress continues to be made in our understanding of the pathways that control the apical (top) geometry of epithelial cells, we know comparatively little about those that control cell basal (bottom) geometry. To examine this issue, we used the fly ommatidium, which is the basic visual unit of the compound eye. The ommatidium is shaped as a hexagonal prism, and generating this three-dimensional structure requires ommatidial cells to adopt specific apical and basal polygonal geometries. Using this model system, we find that generating cell type-specific basal geometries starts with patterning of the basement membrane, whereby Laminin accumulates at discrete locations across the basal surface of the retina. We show that the Dystroglycan surface receptor promotes this localized Laminin accumulation. Moreover, our results reveal that localized accumulation of Laminin-Dystroglycan induces polarization of Integrin adhesion in ommatidial cells. This underpins cell basal geometry remodeling by anchoring the basal surface of cells to the basement membrane at specific, discrete locations. Altogether, our work shows that patterning of a basement membrane by generating discrete Laminin domains, can direct Integrin adhesion. In the retina, this pathway generates specific basal polygonal geometries to organize a complex multicellular structure in three-dimensions.