α-integrins dictate distinct modes of type IV collagen recruitment to basement membranes

Basement membranes (BMs) are cell-associated extracellular matrices that support tissue integrity, signaling, and barrier properties. Type IV collagen is critical for BM mechanical and signaling functions, yet how it is directed into BMs in vivo is unclear. Through live-cell imaging of endogenous localization, conditional knockdown, and misexpression experiments, we uncovered distinct mechanisms of integrin-mediated collagen recruitment to Caenorhabditis elegans gonadal and pharyngeal BMs. The putative laminin-binding INA-1/{beta}PAT-3 integrin was selectively activated in the gonad and recruited laminin, which directed moderate collagen incorporation. In contrast, the putative Arg-Gly-Asp (RGD)-binding PAT-2/{beta}PAT-3 integrin was activated in the pharynx and recruited high levels of collagen independent of laminin. Through an RNAi screen, we further identified the small GTPase RAP-3 (Rap1) as a pharyngeal-specific PAT-2/PAT-3 activator that modulates collagen levels. Together, these studies demonstrate that tissues can use distinct mechanisms to direct collagen incorporation into BMs to precisely control collagen levels and construct diverse BMs.