The circadian clock serves a time-keeping function to anticipate daily changes in the environment and is used by almost every eukaryote on the planet. The ~24-hour circadian period length is buffered against fluctuations in external conditions, including temperature and nutrient levels, in a ubiquitous phenomenon called compensation. The molecular mechanism underlying period compensation is not well understood in any eukaryotic organism. The long-term goal of this project is to understand temperature compensation (TC), nutritional compensation (NC), and the molecular interactions between compensation effectors and the core clock network using the model eukaryote Neurospora crassa. Much of the current knowledge on circadian biology has come from Neurospora, as its core clock network is functionally homologous to the mammalian clock. Casein kinase activity is required for normal TC in both fungal and animal cells, but additional regulators of TC and the specific targets for phosphorylation by CKs have not been systematically investigated. The clock?s period is also compensated to different concentrations of glucose, which involves transcriptional repressor machinery in Neurospora. It is currently unknown if TC and NC regulatory pathways are distinct, or if the core clock is modified similarly in the presence of fluctuations in environmental conditions. I propose to 1) systematically screen for mutants with defects in TC and NC by leveraging the knockout collection of the Neurospora model system; 2) identify Casein Kinase 2 targets during TC using a chemical genetics and mass spectrometry approach; and 3) model interactions between the core clock network and compensation effectors to determine if computational perturbations match experimental data on circadian period length. The goal of this work is to characterize compensation, a defining feature of eukaryotic circadian clocks. Humans with sleep disorders or shift work exposure, or who continually experience jet-lag, have a higher risk to develop cancer, cardiovascular disease, or metabolic syndrome due to chronic dyssynchrony between their cell-based molecular clocks cycling and environmental light:dark cycles. Thus, an improved mechanistic understanding of how the clock is buffered against environmental changes will have diagnostic and therapeutic utility.
This study will investigate the molecular mechanisms behind compensation of the ~24-hour circadian clock across nutrient and temperature conditions using Neurospora crassa which has long been used as a genetically tractable model system for circadian biology. Due to high levels of functional conservation in circadian clock network components and architecture, findings in Neurospora will directly augment our understanding of circadian rhythms in humans and other eukaryotes. This work has the potential to identify pathways required for proper maintenance of the ~24-hour circadian period length in the face of different nutrient levels and temperatures in the environment, findings that have implications for humans with sleep disorders, shift workers, jet-lag, and other chronobiological conditions.
