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标题：Quasimodo mediates daily and acute light effects on Drosophila clock neuron excitability
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作者：Edgar Buhl ; Adam Bradlaugh ; Maite Ogueta 等
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：2016
卷号：113
期号：47
页码：13486-13491
DOI：10.1073/pnas.1606547113
语种：English
出版社：The National Academy of Sciences of the United States of America
摘要：SignificanceMost organisms developed a circadian clock to adapt their behavior to daily changes of light and temperature. The molecular clock is remarkably conserved across species with much of our current understanding coming from Drosophila studies. To generate circadian behavior, appropriate levels of neuronal electrical activity are crucial, but the regulators of this activity have remained largely elusive. Here we identify three membrane proteins that interact to set the clock neurons to "day" or "night," forming a light-input pathway to the circadian clock. The membrane-anchored extracellular protein Quasimodo affects both the daily changes in physiological properties and light responses of brain clock neurons, possibly acting upstream of the potassium channel Shaw and the Na+, K+, Cl- ion transporter NKCC. We have characterized a light-input pathway regulating Drosophila clock neuron excitability. The molecular clock drives rhythmic electrical excitability of clock neurons, and we show that the recently discovered light-input factor Quasimodo (Qsm) regulates this variation, presumably via an Na+, K+, Cl- cotransporter (NKCC) and the Shaw K+ channel (dKV3.1). Because of light-dependent degradation of the clock protein Timeless (Tim), constant illumination (LL) leads to a breakdown of molecular and behavioral rhythms. Both overexpression (OX) and knockdown (RNAi) of qsm, NKCC, or Shaw led to robust LL rhythmicity. Whole-cell recordings of the large ventral lateral neurons (l-LNv) showed that altering Qsm levels reduced the daily variation in neuronal activity: qsmOX led to a constitutive less active, night-like state, and qsmRNAi led to a more active, day-like state. Qsm also affected daily changes in K+ currents and the GABA reversal potential, suggesting a role in modifying membrane currents and GABA responses in a daily fashion, potentially modulating light arousal and input to the clock. When directly challenged with blue light, wild-type l-LNvs responded with increased firing at night and no net response during the day, whereas altering Qsm, NKKC, or Shaw levels abolished these day/night differences. Finally, coexpression of ShawOX and NKCCRNAi in a qsm mutant background restored LL-induced behavioral arrhythmicity and wild-type neuronal activity patterns, suggesting that the three genes operate in the same pathway. We propose that Qsm affects both daily and acute light effects in l-LNvs probably acting on Shaw and NKCC.
关键词：circadian rhythms ; light input ; membrane excitability ; GABA reversal potential ; potassium currents