Circadian and Circatidal Rhythms of Protein Abundance in the Intertidal Mussel Mytilus californianus
DOI: https://doi.org/10.15368/theses.2016.156
Available at: https://digitalcommons.calpoly.edu/theses/1683
Date of Award
12-2016
Degree Name
MS in Biological Sciences
Department/Program
Biological Sciences
Advisor
Lars Tomanek
Abstract
The intertidal zone is a dynamic environment that fluctuates with the 12.4-h tidal and 24-h light/dark cycle to predictably alter food availability, temperature, air exposure, wave action, oxygen partial pressure, and osmotic conditions. Intertidal sessile bivalves exhibit behavioral or physiological changes to minimize the persistent challenges of fluctuating environmental conditions, such as adjusting gaping behavior and heart rate. At the cellular level, transcriptomic studies on mussels’ baseline circadian and circatidal rhythms have determined that the circadian rhythm is the dominant transcriptional rhythm. However, as proteins reflect the basic molecular phenotype of an organism and their abundance may differ greatly from that of mRNA, these methods could fail to detect important cyclical changes in the proteome that cope with the regular stress of tidal rhythms. For this study, we acclimated intertidal Mytilus californianus to circadian (12:12 h light/dark cycle) and circatidal (6:6 h tidal cycle) conditions in a tidal simulator and sampled gill tissue from mussels every 2 h for 48 h for proteomic analysis. Approximately 86% of the proteins that were detected exhibited rhythmicity over the time course. The circadian cycle primarily determined the cyclic abundance of energy metabolism proteins, pivoting around the transition to the nighttime high tide. The tidal cycle contributed to alterations in cytoskeletal components, ER protein processing and vesicular trafficking, extracellular matrix and immune proteins, and oxidative stress and chaperoning proteins. We also found evidence that post-translational modifications may be important for driving these rhythms, as acetylation and phosphorylation motifs were enriched in the rhythmic proteins and we identified rhythms in elements of methylation, mitochondrial peptide processing, and acylation. These dynamic changes in proteins across numerous functional categories indicate that the combination of circadian and tidal cycles drive complex cellular changes to coordinate processes in a changing environment. This variation clearly shows that differential expression studies and biomonitoring efforts cannot assume a static baseline of cellular conditions in intertidal mussels.