title: The MAP kinase p38 is part of Drosophila melanogaster's circadian clock.
abstract: All organisms have to adapt to acute as well as to regularly occurring changes in the environment. To deal with these major challenges organisms evolved two fundamental mechanisms: the p38 mitogen-activated protein kinase (MAPK) pathway, a major stress pathway for signaling stressful events, and circadian clocks to prepare for the daily environmental changes. Both systems respond sensitively to light. Recent studies in vertebrates and fungi indicate that p38 is involved in light-signaling to the circadian clock providing an interesting link between stress-induced and regularly rhythmic adaptations of animals to the environment, but the molecular and cellular mechanisms remained largely unknown. Here, we demonstrate by immunocytochemical means that p38 is expressed in Drosophila melanogaster's clock neurons and that it is activated in a clock-dependent manner. Surprisingly, we found that p38 is most active under darkness and, besides its circadian activation, additionally gets inactivated by light. Moreover, locomotor activity recordings revealed that p38 is essential for a wild-type timing of evening activity and for maintaining ∼ 24 h behavioral rhythms under constant darkness: flies with reduced p38 activity in clock neurons, delayed evening activity and lengthened the period of their free-running rhythms. Furthermore, nuclear translocation of the clock protein Period was significantly delayed on the expression of a dominant-negative form of p38b in Drosophila's most important clock neurons. Western Blots revealed that p38 affects the phosphorylation degree of Period, what is likely the reason for its effects on nuclear entry of Period. In vitro kinase assays confirmed our Western Blot results and point to p38 as a potential "clock kinase" phosphorylating Period. Taken together, our findings indicate that the p38 MAP Kinase is an integral component of the core circadian clock of Drosophila in addition to playing a role in stress-input pathways.
authors.affiliation: Neurobiology and Genetics, Biocenter, University of Würzburg, Würzburg, Germany.
authors.forename: Verena
authors.initials: V
authors.lastname: Dusik
authors.affiliation: Neurobiology and Genetics, Biocenter, University of Würzburg, Würzburg, Germany.
authors.forename: Pingkalai R
authors.initials: PR
authors.lastname: Senthilan
authors.affiliation: Institute of Medical Radiation and Cell Research, University of Würzburg, Würzburg, Germany.
authors.forename: Benjamin
authors.initials: B
authors.lastname: Mentzel
authors.affiliation: Neurobiology and Genetics, Biocenter, University of Würzburg, Würzburg, Germany.
authors.forename: Heiko
authors.initials: H
authors.lastname: Hartlieb
authors.affiliation: Institute of Zoology, University of Regensburg, Regensburg, Germany.
authors.forename: Corinna
authors.initials: C
authors.lastname: Wülbeck
authors.affiliation: Graduate School of Natural Science and Technology, Okayama University, Okayama, Japan.
authors.forename: Taishi
authors.initials: T
authors.lastname: Yoshii
authors.affiliation: Institute of Medical Radiation and Cell Research, University of Würzburg, Würzburg, Germany.
authors.forename: Thomas
authors.initials: T
authors.lastname: Raabe
authors.affiliation: Neurobiology and Genetics, Biocenter, University of Würzburg, Würzburg, Germany.
authors.forename: Charlotte
authors.initials: C
authors.lastname: Helfrich-Förster
mesh_terms: D000818:Animals; D057906:Circadian Clocks / Q000235:genetics* / Q000502:physiology; D002940:Circadian Rhythm / Q000502:physiology; D003624:Darkness; D004331:Drosophila melanogaster / Q000235:genetics / Q000502:physiology*; D008027:Light; D009043:Motor Activity / Q000235:genetics* / Q000502:physiology; D009474:Neurons / Q000378:metabolism / Q000502:physiology; D010766:Phosphorylation; D013312:Stress, Physiological / Q000235:genetics; D048051:p38 Mitogen-Activated Protein Kinases / Q000235:genetics*
chemical_list: D048051:p38 Mitogen-Activated Protein Kinases