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Date of Graduation
Master of Science (MS)
Department of Biology
Timothy Alan Bloss
The function of a protein is a direct consequence of its final structure, which is achieved by protein-folding processes that generate a tertiary state through the juxtaposition of locally formed secondary structures. Because all cells need functional proteins to survive, each contains robust and redundant mechanisms that regulate the folding of newly forming proteins, and the refolding of misfolded proteins that are often generated during stress. Essential to these mechanisms, chaperones are proteins that aid in protein folding of nascent and misfolding protein without being incorporated in the final structure. One chaperone complex, the nascent polypeptide-associated complex (NAC), aids in the folding and translocation of nascent peptide chains during translation. Reflecting its importance to protein folding and therefore survival, complete removal of the NAC is embryonic lethal in a number of metazoans, including Caenorhabditis elegans, while depletion is enough to stimulate up-regulation of hsp-4, an unfolded protein response (UPR) marker that mitigates misfolded protein stress in the ER. To discern the relationship between the NAC and the UPR in the context of misfolded protein stress management, I depleted the NAC in C. elegans embryos deficient for specific elements of the UPR and determined subsequent effects on stress-induced phenotypes. Depletion of either C. elegans NAC subunit (ICD-1 or ICD-2) in select UPR knock-out mutants (IRE1, XBP-1, PERK and ATF6) resulted in changes in apoptosis, autophagy, morphology, and embryonic development that provided insights into the contributions of different UPR elements to these phenotypes. Through these studies, I determined IRE1 plays the most salient role in the UPR initiated upon depletion of the NAC, being directly involved in both the promotion of apoptosis and the maintenance of embryonic development during ER-specific misfolded protein stress. PERK/PEK-1 and ATF6 also contribute to the UPR in NAC-depleted embryos, but to a lesser extent. Overall, these studies provide evidence of a direct relationship between two essential stress-management systems responsible for the maintenance of protein homeostasis in all cells.
Murray, Caylin S., "Profile of the unfolded protein response in C. elegans depleted of the translational chaperone, NAC." (2014). Masters Theses. 2.