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|Title:||ROLES OF THE ATYPICAL MAP KINASES ERK3 AND ERK4 IN THE CIRCADIAN CLOCK|
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|Authors/Affiliations:||2 Jean-François Poirier-Héon*; 1 Justine Rousseau; 1 Benjamin Turgeon; 1 Sylvain Meloche; 2 Nicolas Cermakian; |
1 Institut de Recherche en Immunologie et Cancérologie, Université de Montréal; 2 Institut Universitaire de Santé Mentale Douglas, Montréal, QC, Canada
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|Content:||Circadian rhythms are primordial for health, and their dysfunction is associated with sleep disorders, mood disorders, and cancer. The suprachiasmatic nucleus, the master clock in mammals, allows the synchronization of daily activities to the outside world by interpreting exterior time cues such as light. The Extracellular Regulated Kinases 1 and 2 (ERK1/2), which belong to the Mitogen Activated Protein Kinases (MAPK) familly, have been suggested to be involved in this synchronization phenomenon. Two atypical members of this family, ERK3 and ERK4, were shown to be highly expressed in the brain, yet their physiological function remains unknown. In this study, we have evaluated the function of ERK3 and ERK4 in the circadian clock.|
1- To test the hypothesis that ERK4 plays a role in the circadian clock and in the response to light.
2- Test the expression pattern of clock genes in fibroblasts lacking the Erk3 and Erk4 genes.
1- Erk4-/- mice of C57BL6/129Sv background (n=4), and wild-type littermates (n=5) were put in running wheels and subjected to different light treatments, such as entrainment to12h-12h light-dark (LD) cycle, constant darkness, constant light, and light pulses.
2- Mouse Embryo Fibroblasts (MEFs) from Erk3-/- and Erk4-/- mice were treated with a serum shock (50% horse serum for 2h) and harvested at 16 time points over 52 hours. RNA was extracted and tested for clock gene (Rev-Erb) expression by quantitative PCR.
Results and Conclusions:
1- Erk4-/- mice had lower observed levels of locomotor activity, initiated their activity period later than Erk4+/+ mice, and exhibited larger decreases in activity during a 3-h masking light pulse. After a 6h delay of the light/dark schedule, the onset of activity of Erk4-/- mice shifted very rapidly to the new schedule, compared to Erk4+/+ mice. Erk4-/- mutation did not affect the light-pulse induced phase-shifts, and the free-running period. These data are consistent with a role for ERK4 in the masking effects of light on locomotor activity, but not in the circadian clock.
2- The Erk3-/- and Erk4-/- MEF lines displayed a lower initial induction of the Rev-Erb clock gene in response to serum shock, and 48 hours after the stimulation, levels of clock genes were found to be higher in both Erk3-/- and Erk4-/- cell lines. This could be explained by a slower desynchronization of Erk3-/- and Erk4-/- mutant cell lines.
Further work with larger groups of mice from a more homogeneous background and of combined genotypes will be needed to confirm these preliminary results. This study is to our knowledge the first to characterize the circadian and behavioral phenotypes of mice and fibroblasts mutant for the atypical MAP kinases, and will thus improve our understanding of the physiological role of these proteins.
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