Hemicentin mediated type IV collagen assembly strengthens juxtaposed basement membrane linkage

Basement membrane (BM) matrices surround and separate most tissues. However, through poorly understood mechanisms, BMs of adjacent tissues can also stably link to support organ structure and function. Using endogenous knock-in fluorescent proteins, conditional RNAi, optogenetics, and quantitative live imaging, we identified matrix proteins mediating a BM linkage (B-LINK) between the uterine utse and epidermal seam cell BMs in Caenorhabditis elegans that supports the uterus during egg-laying. We found that hemicentin is secreted by the utse and promotes fibulin-1 assembly to jointly initiate the B-LINK. During egg-laying, however, both proteins decline in levels and are not required for B-LINK maintenance. Instead, we discovered that hemicentin also promotes type IV collagen assembly, which accumulates to high levels during egg-laying and sustains the B-LINK during the mechanically active egg-laying period. This work reveals mechanisms underlying BM-BM connection maturation and identifies a crucial function for hemicentin and fibulin-1 in initiating attachment and type IV collagen in strengthening this specialized form of tissue linkage. Summary Tissue attachment through linking juxtaposed basement membranes (BMs) is crucial for the structure and function of many organs. Gianakas et al. identify a key role for hemicentin and fibulin-1 in initiating BM-BM attachment and type IV collagen in stabilizing this linkage and allowing it to resist high mechanical loads.