Available at: https://digitalcommons.calpoly.edu/theses/3050
Date of Award
6-2025
Degree Name
MS in Biological Sciences
Department/Program
Biological Sciences
College
College of Science and Mathematics
Advisor
Lars Tomanek
Advisor Department
Biological Sciences
Advisor College
College of Science and Mathematics
Abstract
The ecological factors affecting the heat-shock response have been well investigated over the last decades. However, the effect of food availability has not received much attention despite a likely role in modifying stress tolerance limits. Here we acclimated the intertidal mussel Mytilus californianus to four conditions of low–high food, nearshore (low) and aquaculture (high) phytoplankton levels, combined with low-high (20 °C and 30 °C) aerial temperatures. We simulated circadian-entrained circatidal rhythms, before exposing whole mussels to an acute 33 °C 6 h aerial heat stress and allowed for 1 h and 24 h recovery at acclimation conditions. A parallel group in the same experiment was simultaneously exposed to sirtuin inhibitors; although mentioned briefly, this aspect will not the focus in the present thesis.
Our results demonstrate the fundamental role of food availability in attenuating proteomic changes in core carbohydrate and one carbon metabolism, indicating the folate and methionine cycles as central hubs for providing precursors for histone methyltransferases, and producing purines that likely serve as indicators of energy status. We confirm the importance of food availability on oxidative stress responses, especially the scavenging of hydrogen peroxide and the maintenance of reduced glutathione levels. While low food induced the canonical complement of heat-shock proteins, with an emphasis on endoplasmic reticulum chaperones, it was several subunits of the chaperone-containing T-complex, mainly responsible for folding of cytoskeletal proteins, that showed acclimation-specific responses. Similarly, several proteasomal subunits increased across acclimation groups, while the ubiquitin receptor ADRM (Rpn13) varied in response, indicating changes in the type of protease activity. Histone modifiers such as histone kinases and high-mobility groups proteins were prevalent in all groups, specifically in high temperature – low food mussels. Heat stress also induced different splicing factors and heterogeneous nuclear ribonucleoproteins indicating graded differences in alternative splicing among acclimation groups. Within the translational space, changes in ribosomal protein subunits suggest enhanced mRNA selectivity while translation initiation proteins were stable and only elongation factors increased. Cytoskeletal changes indicated actin stress fiber formation in addition to enhanced cross-linking, bundling, and reinforcement of cell adhesion attachments of actin fibers. While we identified members of many signaling pathways, specific increases in p38 MAPK and stress-activated protein kinase (cJun N-terminal kinase) suggest that high aerial temperatures better prepared mussels for an acute heat stress. The MAPK module may also modify prostaglandin synthesis, the role of which we can only hypothesize. While low temperature-low food (LTLF) induced the full complement, both low temperature-high food (LTHF) and high temperature-low food (HTLF) were prepared to limit the response, while high temperature-high food (HTHF) mussels showed an in-between stress response, leaving us to hypothesize there is a trade-off to high food levels in preparation for an acute stress response.