Researchers from the University of Bristol have gained a new insight into how the circadian clock responds to changes in temperature.
With collaborators from University College London, 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.
Dr James Hodge, senior lecturer in the School of Physiology and Pharmacology, said: ‘The circadian clock is basically a timer that allows an organism – be that a fruit fly or a human – to adjust their behaviour 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.
Dr. Ralf Stanewsky, leader of the UCL-based research team, said: ‘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.’
Source: Simon Davies – University of Bristol
Image Credit: The image is adapted from the University of Bristol press release
Original Research: Abstract for “Drosophila Ionotropic Receptor 25a mediates circadian clock resetting by temperature” by Chenghao Chen, Edgar Buhl, Min Xu, Vincent Croset, Johanna S. Rees, Kathryn S. Lilley, Richard Benton, James J. L. Hodge and Ralf Stanewsky in Nature. Published online November 18 doi:10.1038/nature16148
Drosophila Ionotropic Receptor 25a mediates circadian clock resetting by temperature
Circadian clocks are endogenous timers adjusting behaviour and physiology with the solar day1. Synchronized circadian clocks improve fitness2 and are crucial for our physical and mental well-being3. Visual and non-visual photoreceptors are responsible for synchronizing circadian clocks to light4, 5, but clock-resetting is also achieved by alternating day and night temperatures with only 2–4 °C difference6, 7, 8. This temperature sensitivity is remarkable considering that the circadian clock period (~24 h) is largely independent of surrounding ambient temperatures1, 8. Here we show that Drosophila Ionotropic Receptor 25a (IR25a) is required for behavioural synchronization to low-amplitude temperature cycles. This channel is expressed in sensory neurons of internal stretch receptors previously implicated in temperature synchronization of the circadian clock9. IR25a is required for temperature-synchronized clock protein oscillations in subsets of central clock neurons. Extracellular leg nerve recordings reveal temperature- and IR25a-dependent sensory responses, and IR25a misexpression confers temperature-dependent firing of heterologous neurons. We propose that IR25a is part of an input pathway to the circadian clock that detects small temperature differences. This pathway operates in the absence of known ‘hot’ and ‘cold’ sensors in the Drosophila antenna10, 11, revealing the existence of novel periphery-to-brain temperature signalling channels.
“Drosophila Ionotropic Receptor 25a mediates circadian clock resetting by temperature” by Chenghao Chen, Edgar Buhl, Min Xu, Vincent Croset, Johanna S. Rees, Kathryn S. Lilley, Richard Benton, James J. L. Hodge and Ralf Stanewsky in Nature. Published online November 18 doi:10.1038/nature16148