ECM proteins shape topographical patterns in the basement membrane of Drosophila wing discs

The basal surface of epithelial tissues is attached to a thin network of macromolecules known as the basement membrane. The core components of the basement membrane - Collagen IV, Laminin, Perlecan, and Nidogen - are conserved extracellular matrix (ECM) proteins across species. However, the topography of basement membranes and the contribution of individual core components to its establishment remain poorly understood. Here, we used AFM-aided PeakForce tapping to analyze the topography of the basement membrane of Drosophila larval wing discs. We identified a self-affine surface topography, appearing structurally similar across multiple scales. Further, the topography is characterized by thin fiber-like structures that are intermittently aligned with a preferred orientation along the anterior-posterior axis. During larval development, the amplitude of surface patterns overall decreases, whereas the abundance of basement membrane components increases. Using targeted knockdown experiments, we show that Collagen IV is essential for the formation of fiber-like structures, while Laminin and Collagen IV appear to smooth or level out large-scale groove-like patterns. In contrast, Nidogen contributes to the maintenance of these grooves, and Perlecan increases surface pattern amplitudes at all length scales. Our findings reveal distinct topographical features in the basement membrane, whose amplitude and organization depend on its specific molecular composition.