Stricker, A. | bioRxiv Science

bioRxiv2023

Piezo initiates transient production of collagen IV to repair damaged basement membranes

Basement membranes are extracellular matrix sheets separating tissue layers and providing mechanical support, and Collagen IV (Col4) is their most abundant protein. Although basement membranes are repaired after damage, little is known about repair, including whether and how damage is detected, what cells repair the damage, and how repair is controlled to avoid fibrosis. Using the intestinal basement membrane of adult Drosophila as a model, we show that after basement membrane damage, there is a sharp increase in enteroblasts transiently expressing Col4, or "matrix mender" cells. Enteroblast-derived Col4 is specifically required for matrix repair. The increase in matrix mender cells requires the mechanosensitive ion channel Piezo, expressed in intestinal stem cells. Matrix menders are induced by the loss of matrix stiffness, as specifically inhibiting Col4 crosslinking is sufficient for Piezo-dependent induction of matrix mender cells. Our data suggest that epithelial stem cells control basement membrane integrity by monitoring stiffness.

cell biology↗

bioRxiv2019

RHO-1 and the Rho GEF RHGF-1 interact with UNC-6/Netrin signaling to regulate growth cone protrusion and microtubule organization in C. elegans

UNC-6/Netrin is a conserved axon guidance cue that directs growth cone migrations in the dorsal-ventral axis of C. elegans and in the vertebrate spinal cord. UNC-6/Netrin is expressed in ventral cells, and growth cones migrate ventrally toward or dorsally away from UNC-6/Netrin. Recent studies of growth cone behavior during outgrowth in vivo in C. elegans have led to a polarity/protrusion model in directed growth cone migration away from UNC-6/Netrin. In this model, UNC-6/Netrin first polarizes the growth cone via the UNC-5 receptor, leading to dorsally biased protrusion and F-actin accumulation. UNC-6/Netrin then regulates protrusion based on this polarity. The receptor UNC-40/DCC drives protrusion dorsally, away from the UNC-6/Netrin source, and the UNC-5 receptor inhibits protrusion ventrally, near the UNC-6/Netrin source, resulting in dorsal migration. UNC-5 inhibits protrusion in part by excluding microtubules from the growth cone, which are pro-protrusive. Here we report that the RHO-1/RhoA GTPase and its activator GEF RHGF-1 inhibit growth cone protrusion and MT accumulation in growth cones, similar to UNC-5. However, growth cone polarity of protrusion and F-actin were unaffected by RHO-1 and RHGF-1. Thus, RHO-1 signaling acts specifically as a negative regulator of protrusion and MT accumulation, and not polarity. Genetic interactions suggest that RHO-1 and RHGF-1 act with UNC-5, as well as with a parallel pathway, to regulate protrusion. The cytoskeletal interacting molecule UNC-33/CRMP was required for RHO-1 activity to inhibit MT accumulation, suggesting that UNC-33/CRMP might act downstream of RHO-1. In sum, these studies describe a new role of RHO-1 and RHGF-1 in regulation of growth cone protrusion by UNC-6/Netrin.\n\nAuthor SummaryNeural circuits are formed by precise connections between axons. During axon formation, the growth cone leads the axon to its proper target in a process called axon guidance. Growth cone outgrowth involves asymmetric protrusion driven by extracellular cues that stimulate and inhibit protrusion. How guidance cues regulate growth cone protrusion in neural circuit formation is incompletely understood. This work shows that the signaling molecule RHO-1 acts downstream of the UNC-6/Netrin guidance cue to inhibit growth cone protrusion in part by excluding microtubules from the growth cone, which are structural elements that drive protrusion.

neuroscience↗