The Spatiotemporal Distribution of SPARC and Collagen IV in the Secretory Pathway and Evidence of a Functional Relationship During Extracellular Collagen IV Polymerization

Basement membranes (BMs) are a hallmark feature of multicellular organisms and support essential developmental events. Collagen IV is the major structural component of BMs, however, its spatiotemporal assembly into stereotypic lattice networks is poorly understood. SPARC, a collagen IV-binding glycoprotein, is enriched in BMs of Drosophila melanogaster. SPARC is hypothesized to be an extracellular chaperone-like protein, whereby it prevents premature collagen IV polymerization. In this study, I demonstrate that SPARC and collagen IV co-localize primarily in the trans-Golgi network prior to secretion. Moreover, SPARC reduces premature nucleation of collagen IV molecules in cultured hemocytes seeded on a laminin matrix, but is not required for the establishment of collagen IV-rich BMs in the embryo. To gain further insight on the functional relationship between SPARC and collagen IV, CRISPR/Cas9 sparc mutants were generated. This genetic tool will be used to unmask SPARC structural domains responsible for collagen IV assembly and BM homeostasis.M.Sc