Synopsis: Robust Yet Flexible Clocks
In most living organisms, biochemical mechanisms keep body metabolism and sleep patterns synchronized with the night-to-day cycle. Such circadian clocks have to be robust enough to keep a 24-hour pace under fluctuating light or temperature, but also plastic enough to adapt to shifts in the daily cycle that come from, for instance, seasonal changes. But how are these seemingly conflicting properties simultaneously achieved? Theoretical work by researchers at the University of Tokyo, Japan, suggests that the same mechanisms that make a clock robust also enhance its plasticity.
Tetsuhiro Hatakeyama and Kunihiko Kaneko analyzed two models that together represent the vast majority of known circadian clock mechanisms in nature. In such models, cyclical changes in external parameters like temperature or light affect different stages of the biochemical reactions that regulate bodily functions.
Focusing on temperature as a control parameter, the authors analyzed its effect on the rate of key biochemical steps in circadian clocks. They defined a measure of a clock’s robustness as the inverse of the variation of the clock period with temperature and calculated this quantity for the two clock types. The authors then exposed the clocks to cyclic temperature changes and computed how quickly the clocks were entrained by such cycles. Solving the nonlinear equations that describe the clocks in the two different models, the researchers found that the most robust clocks were also the most plastic, that is, the quickest to adjust to shifts in the temperature cycle. They also derived a universal and quantitative law that links robustness and plasticity for all circadian clocks.
This research is published in Physical Review Letters.