title: Phosphorylation of a central clock transcription factor is required for thermal but not photic entrainment.
abstract: Transcriptional/translational feedback loops drive daily cycles of expression in clock genes and clock-controlled genes, which ultimately underlie many of the overt circadian rhythms manifested by organisms. Moreover, phosphorylation of clock proteins plays crucial roles in the temporal regulation of clock protein activity, stability and subcellular localization. dCLOCK (dCLK), the master transcription factor driving cyclical gene expression and the rate-limiting component in the Drosophila circadian clock, undergoes daily changes in phosphorylation. However, the physiological role of dCLK phosphorylation is not clear. Using a Drosophila tissue culture system, we identified multiple phosphorylation sites on dCLK. Expression of a mutated version of dCLK where all the mapped phospho-sites were switched to alanine (dCLK-15A) rescues the arrythmicity of Clk(out) flies, yet with an approximately 1.5 hr shorter period. The dCLK-15A protein attains substantially higher levels in flies compared to the control situation, and also appears to have enhanced transcriptional activity, consistent with the observed higher peak values and amplitudes in the mRNA rhythms of several core clock genes. Surprisingly, the clock-controlled daily activity rhythm in dCLK-15A expressing flies does not synchronize properly to daily temperature cycles, although there is no defect in aligning to light/dark cycles. Our findings suggest a novel role for clock protein phosphorylation in governing the relative strengths of entraining modalities by adjusting the dynamics of circadian gene expression.
authors.affiliation: Neuroscience Graduate Program, Department of Biomedical Sciences, Ajou University School of Medicine, Suwon, Kyunggi-do, Republic of Korea; Department of Brain Science, Ajou University School of Medicine, Suwon, Kyunggi-do, Republic of Korea.
authors.forename: Euna
authors.initials: E
authors.lastname: Lee
authors.affiliation: Department of Brain Science, Ajou University School of Medicine, Suwon, Kyunggi-do, Republic of Korea.
authors.forename: Eun Hee
authors.initials: EH
authors.lastname: Jeong
authors.affiliation: Neuroscience Graduate Program, Department of Biomedical Sciences, Ajou University School of Medicine, Suwon, Kyunggi-do, Republic of Korea.
authors.forename: Hyun-Jeong
authors.initials: HJ
authors.lastname: Jeong
authors.affiliation: Department of Molecular Biology and Biochemistry, Rutgers University, Center for Advanced Biotechnology and Medicine, Piscataway, New Jersey, United States of America.
authors.forename: Evrim
authors.initials: E
authors.lastname: Yildirim
authors.affiliation: Laboratory of Chronobiology, Charité-Universitätsmedizin, Berlin, Germany.
authors.forename: Jens T
authors.initials: JT
authors.lastname: Vanselow
authors.affiliation: Texas A&M University Department of Biology and Center for Biological Clocks Research, College Station, Texas, United States of America.
authors.forename: Fanny
authors.initials: F
authors.lastname: Ng
authors.affiliation: Texas A&M University Department of Biology and Center for Biological Clocks Research, College Station, Texas, United States of America.
authors.forename: Yixiao
authors.initials: Y
authors.lastname: Liu
authors.affiliation: Texas A&M University Department of Biology and Center for Biological Clocks Research, College Station, Texas, United States of America.
authors.forename: Guruswamy
authors.initials: G
authors.lastname: Mahesh
authors.affiliation: Laboratory of Chronobiology, Charité-Universitätsmedizin, Berlin, Germany.
authors.forename: Achim
authors.initials: A
authors.lastname: Kramer
authors.affiliation: Texas A&M University Department of Biology and Center for Biological Clocks Research, College Station, Texas, United States of America.
authors.forename: Paul E
authors.initials: PE
authors.lastname: Hardin
authors.affiliation: Department of Molecular Biology and Biochemistry, Rutgers University, Center for Advanced Biotechnology and Medicine, Piscataway, New Jersey, United States of America.
authors.forename: Isaac
authors.initials: I
authors.lastname: Edery
authors.affiliation: Neuroscience Graduate Program, Department of Biomedical Sciences, Ajou University School of Medicine, Suwon, Kyunggi-do, Republic of Korea; Department of Brain Science, Ajou University School of Medicine, Suwon, Kyunggi-do, Republic of Korea.
authors.forename: Eun Young
authors.initials: EY
authors.lastname: Kim
mesh_terms: D000409:Alanine / Q000235:genetics; D000818:Animals; D056926:CLOCK Proteins / Q000096:biosynthesis / Q000235:genetics*; D002940:Circadian Rhythm / Q000235:genetics*; D029721:Drosophila Proteins / Q000096:biosynthesis / Q000235:genetics*; D004331:Drosophila melanogaster / Q000235:genetics* / Q000254:growth & development; D018507:Gene Expression Regulation, Developmental; D009154:Mutation; D010766:Phosphorylation / Q000235:genetics; D012333:RNA, Messenger / Q000096:biosynthesis
chemical_list: C120526:Clk protein, Drosophila; D029721:Drosophila Proteins; D012333:RNA, Messenger; D056926:CLOCK Proteins; D000409:Alanine