TY  - JOUR
A1  - Beck, Katherina
A1  - Hovhanyan, Anna
A1  - Menegazzi, Pamela
A1  - Helfrich-Förster, Charlotte
A1  - Raabe, Thomas
T1  - Drosophila RSK Influences the Pace of the Circadian Clock by Negative Regulation of Protein Kinase Shaggy Activity
JF  - Frontiers in Molecular Neuroscience
N2  - Endogenous molecular circadian clocks drive daily rhythmic changes at the cellular, physiological, and behavioral level for adaptation to and anticipation of environmental signals. The core molecular system consists of autoregulatory feedback loops, where clock proteins inhibit their own transcription. A complex and not fully understood interplay of regulatory proteins influences activity, localization and stability of clock proteins to set the pace of the clock. This study focuses on the molecular function of Ribosomal S6 Kinase (RSK) in the Drosophila melanogaster circadian clock. Mutations in the human rsk2 gene cause Coffin–Lowry syndrome, which is associated with severe mental disabilities. Knock-out studies with Drosophila ortholog rsk uncovered functions in synaptic processes, axonal transport and adult behavior including associative learning and circadian activity. However, the molecular targets of RSK remain elusive. Our experiments provide evidence that RSK acts in the key pace maker neurons as a negative regulator of Shaggy (SGG) kinase activity, which in turn determines timely nuclear entry of the clock proteins Period and Timeless to close the negative feedback loop. Phosphorylation of serine 9 in SGG is mediated by the C-terminal kinase domain of RSK, which is in agreement with previous genetic studies of RSK in the circadian clock but argues against the prevailing view that only the N-terminal kinase domain of RSK proteins carries the effector function. Our data provide a mechanistic explanation how RSK influences the molecular clock and imply SGG S9 phosphorylation by RSK and other kinases as a convergence point for diverse cellular and external stimuli.
KW  - circadian clock
KW  - Period
KW  - Timeless
KW  - Shaggy kinase
KW  - RSK
KW  - Coffin–Lowry syndrome
Y1  - 2018
U6  - http://nbn-resolving.de/urn/resolver.pl?urn:nbn:de:bvb:20-opus-196034
SN  - 1662-5099
VL  - 11
IS  - 122
ER  - 
TY  - JOUR
A1  - Dusik, Verena
A1  - Senthilan, Pingkalai R.
A1  - Mentzel, Benjamin
A1  - Hartlieb, Heiko
A1  - Wülbeck, Corina
A1  - Yoshii, Taishi
A1  - Raabe, Thomas
A1  - Helfrich-Förster, Charlotte
T1  - The MAP Kinase p38 Is Part of Drosophila melanogaster's Circadian Clock
JF  - PLoS Genetics
N2  - 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.
KW  - in vitro kinase assay
KW  - biological locomotion
KW  - circadian oscillators
KW  - MAPK signaling cascades
KW  - circadian rhythms
KW  - drosophila melanogaster
KW  - neurons
KW  - phosphorylation
Y1  - 2014
U6  - http://nbn-resolving.de/urn/resolver.pl?urn:nbn:de:bvb:20-opus-119433
SN  - 1553-7404
VL  - 10
IS  - 8
ER  -