Quasimodo mediates daily and acute light effects on Drosophila clock neuron excitability.
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: qsmOXled to a constitutive less active, night-like state, and qsmRNAiled 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 ShawOXand NKCCRNAiin 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.
School of Physiology, Pharmacology and Neuroscience, University of Bristol, Bristol BS8 1TD, United Kingdom; e.buhl@bristol.ac.uk r.stanewsky@ucl.ac.uk.|Hatherly Laboratories, University of Exeter Medical School, University of Exeter, Exeter EX4 4PS, United Kingdom.
Edgar
0000-0003-1274-5870
E
Buhl
Department of Cell and Developmental Biology, University College London, London WC1E 6DE, United Kingdom.|School of Biological and Chemical Sciences, Queen Mary College, London E1 4NS, United Kingdom.
Adam
A
Bradlaugh
Department of Cell and Developmental Biology, University College London, London WC1E 6DE, United Kingdom.|Institute for Neuro- and Behavioral Biology, Westfälische Wilhelms University, 48149 Muenster, Germany.
Maite
M
Ogueta
Institute of Neurology, University College London, London WC1N 3BG, United Kingdom.
Ko-Fan
KF
Chen
Department of Cell and Developmental Biology, University College London, London WC1E 6DE, United Kingdom; e.buhl@bristol.ac.uk r.stanewsky@ucl.ac.uk.|Institute for Neuro- and Behavioral Biology, Westfälische Wilhelms University, 48149 Muenster, Germany.
Ralf
R
Stanewsky
School of Physiology, Pharmacology and Neuroscience, University of Bristol, Bristol BS8 1TD, United Kingdom.
James J L
JJ
Hodge
D000483:Alleles; D000818:Animals; D001522:Behavior, Animal; D057906:Circadian Clocks / Q000528:radiation effects*; D029721:Drosophila Proteins / Q000378:metabolism*; D004331:Drosophila melanogaster / Q000235:genetics / Q000502:physiology* / Q000528:radiation effects*; D058851:GPI-Linked Proteins / Q000378:metabolism*; D055785:Gene Knockdown Techniques; D005838:Genotype; D015640:Ion Channel Gating / Q000528:radiation effects; D008027:Light; D008954:Models, Biological; D009474:Neurons / Q000502:physiology* / Q000528:radiation effects*; D011485:Protein Binding / Q000528:radiation effects; D005680:gamma-Aminobutyric Acid / Q000378:metabolism
D029721:Drosophila Proteins; D058851:GPI-Linked Proteins; C560826:QSM protein, Drosophila; D005680:gamma-Aminobutyric Acid
GABA reversal potential; circadian rhythms; light input; membrane excitability; potassium currents