Basement membranes are the oldest, most conserved forms of extracellular matrix and serve to separate tissue layers, direct signals to neighboring cells, insulate tissues from signals, and provide mechanical support. Further, basement membranes are subject to mechanical damage and require repair. Faulty basement membrane repair can aid in the progression of diseases such as asthma and diabetes, and diseases of the basement membrane itself, including Alport syndrome and Goodpasture syndrome. Therefore, understanding how basement membranes repair will be vital to treating these conditions. My work utilizes the Drosophila midgut basement membrane to probe repair dynamics. In Drosophila, all major basement membrane components have been conserved but with less redundancy than mammals. Our lab has developed an assay to reproducibly damage the basement membrane and study the repair process. Following damage, the basement membrane becomes less stiff and less dense, indicated by a mechanical stress/strain assay and electron microscopy, respectively. Previously it was reported that processes required for basement membrane repair are also required to maintain basement membranes that have not been damaged; these processes include continuous matrix synthesis and regulation of enzymes (matrix metalloproteinases and peroxidasin). Thus, it is unclear whether basement membrane damage is actively detected, or instead, passively repaired by homeostatic mechanisms. My preliminary data suggest basement membrane damage is actively detected. Following damage, the synthesis of matrix components is upregulated in a specific subset of gut epithelial cells we call matrix-makers, and these may be the same cells that express a mechanosensory stretch-activated ion channel, Piezo. This raises the possibility that a change in stiffness of damaged basement membranes signals the initiation of repair. Piezo knockout flies are able to assemble and maintain basement membranes in the adult fly, but, excitingly, Piezo knockouts cannot repair basement membranes after damage. This is evidence of a unique mechanism that detects basement membrane damage and initiates repair. I hypothesize that a loss in matrix stiffness triggers basement membrane repair mechanisms. In Aim 1, I propose to characterize a transient cell population responsible for synthesizing new matrix components following basement membrane damage. In Aim 2, I propose to identify the role of Piezo and its response following basement membrane damage. I expect to identify the first mechanism for detecting and repairing basement membranes. Understanding this mechanism will provide fundamental insights into epithelial biology and will be critical to treating and understanding diseases of the basement membrane.