期刊名称：Proceedings of the National Academy of Sciences
印刷版ISSN：0027-8424
电子版ISSN：1091-6490
出版年度：2015
卷号：112
期号：28
页码：8702-8707
DOI：10.1073/pnas.1506093112
语种：English
出版社：The National Academy of Sciences of the United States of America
摘要：SignificanceThe study of laboratory-generated circadian locomotor activity patterns of Drosophila played a critical role in determining how fruitfly (and mammalian) clocks function. However, recent observations of fly activity in the wild challenged many assumptions about how the clock might work. A new prominent summer locomotor component emerged called "A" (afternoon), which replaced the laboratory "siesta." The A component has been criticized by others to be an artifact, but our study here shows that it is genuine and is observed under a variety of simulated natural conditions. The A component is temperature- and clock-dependent and is generated by expression of the internal transient receptor potential A1 thermosensor (TrpA1), revealing a pathway for environmental input to the clock. Under standard laboratory conditions of rectangular light/dark cycles and constant warm temperature, Drosophila melanogaster show bursts of morning (M) and evening (E) locomotor activity and a "siesta" in the middle of the day. These M and E components have been critical for developing the neuronal dual oscillator model in which clock gene expression in key cells generates the circadian phenotype. However, under natural European summer conditions of cycling temperature and light intensity, an additional prominent afternoon (A) component that replaces the siesta is observed. This component has been described as an "artifact" of the TriKinetics locomotor monitoring system that is used by many circadian laboratories world wide. Using video recordings, we show that the A component is not an artifact, neither in the glass tubes used in TriKinetics monitors nor in open-field arenas. By studying various mutants in the visual and peripheral and internal thermo-sensitive pathways, we reveal that the M component is predominantly dependent on visual input, whereas the A component requires the internal thermo-sensitive channel transient receptor potential A1 (TrpA1). Knockdown of TrpA1 in different neuronal groups reveals that the reported expression of TrpA1 in clock neurons is unlikely to be involved in generating the summer locomotor profile, suggesting that other TrpA1 neurons are responsible for the A component. Studies of circadian rhythms under seminatural conditions therefore provide additional insights into the molecular basis of circadian entrainment that would otherwise be lost under the usual standard laboratory protocols.
