Date of Award

2020

Degree Type

Dissertation

Degree Name

Doctor of Philosophy (PhD)

Graduate Group

Cell & Molecular Biology

First Advisor

Meera V. Sundaram

Abstract

Extracellular matrices (ECMs) are layered structures of proteins, lipids, and starches that shape and protect cells. Apical surfaces face the external environment or the inside (lumen) of biological tubes, and are lined by the relatively poorly understood apical ECMs (aECMs). aECMs are critical for shaping tubes and protecting external surfaces. Loss of aECM components is associated with many human diseases, including cardiovascular disease, deafness, and kidney disease. aECMs often form complex, layered structures containing lipids, glycoproteins, and glycosaminoglycans. One abundant family of aECM glycoproteins is that of Zona Pellucida, or ZP, proteins. Some ZP proteins can polymerize but others may trap signaling ligands. aECMs and ZP proteins are crucial for maintaining human health. However, aECM assembly in general, and ZP protein assembly within aECMs in particular, are not well understood. Using the model organism Caenorhabditis elegans, I define the contents of aECMs and investigate how they assemble. Via a forward genetic screen, I identified a set of aECM components that shape several C. elegans tissues. Using genetics and live imaging, I illuminate the kaleidoscopic localization patterns of aECM components. These aECM components include LET-653, a ZP protein, which was the primary focus of my dissertation. I demonstrate that LET-653 shapes multiple C. elegans tubes of vastly different shapes and sizes. I elucidate the novel mechanism of LET-653 assembly into the aECM. I also identify and characterize another aECM protein, DEX-1, which shares many mutant phenotypes with ZP proteins despite containing domains characteristic of basal ECMs. In addition, I demonstrate that the patched-related protein PTR-4, a multi-pass transmembrane protein related to lipid transporters, localizes LET-653 cell-non-autonomously. Lastly, I find that the protease BLI-4 promotes developmentally-timed LET-653 clearance from the aECM. This project offers the most complete view yet of an aECM, with correlations between protein localization, function, and phenotypes.

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