Faulty gene and peripheral tissues affect fruit fly's biological clock
Natural light-dark and temperature cycles synchronise circadian rhythms, or what is commonly called a biological clock. But clock neurons in the brain need input from peripheral tissues in order to be synchronised by temperature, according to new EU-funded research. The results, published in the journal Neuron, pinpoint differences between how light-dark and temperature cycles synchronise the brain clock of the Drosophila fruit fly. The findings are part of the EUCLOCK ('Entrainment of the circadian clock') project, which received EUR 12.3 million under the 'Life sciences, genomics and biotechnology for health' Thematic area of the EU's Sixth Framework Programme (FP6). According to the project's British and German researchers, circadian clocks regulate a number of biological processes that benefit organisms. While these clocks are self-sustained and operate under conditions that never change, they are synchronised with the environment by natural cues called 'zeitgebers', which include light-dark and temperature cycles. 'Circadian clocks regulate many biological processes to occur at beneficial times for the organism,' said Dr Ralf Stanewsky of Queen Mary College at the University of London in the UK. 'Although we know quite a bit about how natural light-dark cycles synchronise the circadian clock of organisms ranging from flies to mammals, little is known about mechanisms of temperature synchronisation,' added the senior author of the study. Until now, researchers have not been able to shed light on which cells or structures have the capacity to detect daily temperature cycles. A lack of information has also fuelled the mystery on how temperature cycle signals reach the brain clock, the researchers said. In a past study, Dr Stanewsky and colleagues successfully identified two mutations in the fruit flies that hindered temperature synchronisation. They discovered a faulty gene, 'nocte', in flies that demonstrated normal light synchronisation but abnormal molecular and behavioural synchronisation to temperature. In this latest research, the team discovered that while light-dark cycles were synchronised in isolated fly brains, temperature cycles were not. They speculated that information from peripheral tissues must be picked up by the brain's circadian clock neurons if temperature synchronisation is to take place. The researchers noted how temperature synchronisation was also hampered by the disruption of nocte in peripheral cells. 'Reducing the function of the gene nocte in chordotonal organs [major fly sensory organs] changes their structure and function and dramatically interferes with temperature synchronisation of behavioural activity,' the study showed. Researchers revealed that other mutations that affect the function of the chordotonal organs also impede temperature synchronisation. This shows how central a role the gene nocte plays in this process, and how the chordotonal organs are important sensory structures, particularly as circadian temperature receptors. 'Our work reveals surprising and important mechanistic differences between light and temperature synchronisation, and advances our understanding of how clock resetting is accomplished in nature,' Dr Stanewsky explained. 'This study demonstrates once again the power of forward genetics in identifying novel factors and mechanisms. Just looking at the nocte DNA sequence, no one would have predicted a function for this gene or the chordotonal organs in temperature synchronisation.' Researchers from the Institute of Zoology at the University of Regensburg in Germany also participated in this study.
Countries
Germany, United Kingdom