Post-Translational Modifications in Animal Circadian Clocks

The circadian clock is a fundamental biological system that synchronizes behavioral and physiological processes such as metabolism and immunity with the 24 h day-night cycle. Disruption of circadian rhythms, often caused by modern lifestyle factors like shift work and jet lag, is closely associated with metabolic and mental disorders. In both mammals and Drosophila, the molecular oscillator consists of conserved transcriptional-translational feedback loops (TTFLs) involving positive and negative regulatory elements that generate rhythmic gene expression. Post-translational modifications (PTMs) of clock proteins play crucial roles in modulating the circadian period length, robustness, and responsiveness to environmental cues. Importantly, casein kinase 1 family-dependent phosphorylation on both positive and negative elements in animal clocks highlights the evolutionary convergence of circadian timekeeping across species. This review focuses on PTMs and related mechanisms in circadian timekeeping and their roles in adapting to environmental and physiological signals in animals.