Role of sex and protein degradation in the circadian clock

Project Summary/Abstract Circadian clocks influence nearly all aspects of mammalian life, aligning our internal physiological process to optimal times of day. Understanding the molecular circuitry keeping circadian time provides insight into how the clock drives overt rhythms and what to fix when the circadian system is disrupted (i.e. during shift work). Circadian time coded in the rhythmic regulation of “clock gene” expression in a negative feedback loop system. Critical to this timing system is the circadian degradation of rhythmically abundant clock proteins, however, these mechanisms have remained elusive. We have begun elucidating these mechanisms by developing a novel functional screening approach designed to identify which E3 ubiquitin ligases degrade which clock proteins. The first screen hit we have recovered, Siah2, has revealed remarkable and unexpected new insights into both clock function by uncovering the unexpected existence of female-specific circadian mechanisms that control metabolism specifically in females. Unfortunately, the vast majority of circadian data available are from male mice; thus, we have broadly started to compare how the circadian system differs between males and females, and across the 4-day estrus cycle (a huge potential but unstudied influence), in mice. Our studies in the liver so far have revealed substantial sex-differences in the landscape of genes regulated across the day between the sexes, and across the estrus-cycle. Furthermore, we have discovered that Siah2 also appears to regulate the circadian clock in several tissues an estrus-cycle dependent manner (i.e., only on the day(s) prior ovulation), providing strong evidence that circadian clock systems have highly sex-specific roles. Therefore, our goals for the next 5 years are to continue filling in the gaps that exist in female circadian biology by further identifying the differences/similarities between the sexes, leverage Siah2 as a tool to understand what these mechanisms do, and why they are different. Understanding sex-differences in circadian clock functions will be critical as the field develops circadian-based therapeutics.