Mechanisms of Type IV Collagen Targeting to Developing Basement Membranes
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Basement membranes (BMs) are cell-associated extracellular matrices that support tissue integrity, signaling, and barrier properties. Type IV collagen is critical for the mechanical and signaling functions of BM. However, due to the challenge of imaging of BMs in vivo, the lethal phenotypes of null mutations of many BM components, and the expanded gene families of BM receptors and matrix components in vertebrates, how collagen is directed to BMs in vivo is not clear. Here, I exploited the visual tractability and small BM receptor and matrix families of the nematode C. elegans, using live-cell imaging of endogenous localization, conditional knockdown, misexpression, and RNAi screening techniques to investigate how the sole C. elegans type IV collagen molecule is recruited to the BMs of growing gonadal and pharyngeal organs during larval development. In Chapter 1, I review BM structure and functions, focusing on type IV collagen; identify gaps in our understanding of how collagen is directed to BMs, and introduce C. elegans as a model to study type IV collagen incorporation into BMs in vivo. In Chapter 2, I discover that the α subunits of the matrix receptor integrin dictate distinct modes of collagen IV recruitment to the C. elegans pharyngeal and gonadal BMs. In Chapter 3, I explore the roles of the matricellular proteins nidogen, agrin, perlecan, and SPARC in the targeting of collagen to pharyngeal and gonadal BMs. In Chapter 4, I identify potentially novel regulators of type IV collagen incorporation into BMs through a genome-scale RNAi screen. Finally, in Chapter 5, I discuss the implications of these findings to our understanding of type IV collagen incorporation into BMs in vivo, relating them to both established and emerging functions of type IV collagen in BMs.
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