University of Bristol researchers have gained a new insight into how the circadian clock responds to changes in temperature.

With collaborators from University College London (UCL), the University of Lausanne, and the University of Cambridge, the researchers discovered that a protein called Ionotropic Receptor 25a (IR25a), an evolutionary relative of Ionotropic Glutamate Receptors, have a key role in entraining the brains of fruit flies to react to small changes in temperature.

Their findings were recently published in the journal Nature.

James Hodge, BSc, PhD, senior lecturer in the School of Physiology and Pharmacology, says in a release: “The circadian clock is basically a timer that allows an organism—be that a fruit fly or a human—to adjust their behavior and physiology according to the time of day. The clocks are controlled both by changes in light and temperature.

“However, the temperature sensitivity for adjusting the clock is remarkable, as the pace of the circadian clock is largely independent of the surrounding ambient temperature. In our experiments with fruit flies, we discovered that IR25a is part of a pathway to the circadian clock that detects small temperature differences. This pathway operates in the absence of known ‘hot’ and ‘cold’ sensors in the fruit fly’s antenna, which points to the existence of periphery-to-brain temperature signalling channels.”

The researchers investigated whether flies lacking IR25a were able to synchronize their circadian clocks to temperature changes. The team’s experiments showed that, when the temperature fluctuations were large, flies lacking IR25a could adapt. However, when the changes in the temperature range were small, the flies lacking IR25a could not adapt.

Ralf Stanewsky, PhD, leader of the UCL-based research team, says: “Our findings reveal a surprising complexity of how temperature signals reset the brain clock. Similar to what has been described for light resetting of the human and fly circadian clock, it seems clear that organisms do not rely on a single pathway, but employ multiple input routes for both temperature and light. This hints to the importance of accurate circadian clock synchronization with the environment, and future work will address how these different input signals are integrated in the brain clock.”