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Light-induced Changes in the Suprachiasmatic Nucleus Transcriptome Regulated by the ERK/MAPK Pathway

ABSTRACT: The mammalian master circadian pacemaker within the suprachiasmatic nucleus (SCN) maintains tight entrainment to the 24 hr light/dark cycle via a sophisticated clock-gated rhythm in the responsiveness of the oscillator to light. Intriguingly, entrainment is not merely a passive response, instead the internal oscillator responds and adjust its own timing to entrainment signals discriminating the time of day. For example, exposure to brief light pulses in the first and final hours of the subjective generate circadian phase delays and advances respectively; whereas similar photic pulses during the subjective day does not modify the phase. A central event in this light entrainment process appears to be the rapid induction of gene expression via the ERK/MAPK pathway. We used microarray-based expression profiling of the suprachiasmatic nucleus to examine the role of MAPK signaling in the light-evoked transcriptional response. We focused on three circadian timepoints that define the unique, clock-time delimited response properties of the SCN to light: the subjective day, early subjective night, and late subjective night.

ORGANISM(S): Mus musculus

PROVIDER: GSE165799 | GEO | 2021/03/24

REPOSITORIES: GEO

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Project description:Seasonal daylength, or circadian photoperiod, is a pervasive environmental signal that profoundly influences physiology and behavior. In mammals, the central circadian clock resides in the suprachiasmatic nuclei (SCN) of the hypothalamus where it receives retinal input and synchronizes, or entrains, organismal physiology and behavior to the prevailing light cycle. The process of entrainment induces sustained plasticity in the SCN, but the molecular mechanisms underlying SCN plasticity are incompletely understood. Entrainment to different photoperiods persistently alters the timing, waveform, period, and light resetting properties of the SCN clock and its driven rhythms. To elucidate novel molecular mechanisms of photoperiod plasticity, we performed RNAseq on whole SCN dissected from mice raised in Long (LD 16:8) and Short (LD 8:16) photoperiods. Fewer rhythmic genes were detected in Long photoperiod and in general the timing of gene expression rhythms was advanced 4-6 hours. However, a few genes showed significant delays, including Gem. There were significant changes in the expression clock-associated gene Timeless and in SCN genes related to light responses, neuropeptides, GABA, ion channels, and serotonin. Particularly striking were differences in the expression of the neuropeptide signaling genes Prokr2 and Cck, as well as convergent regulation of the expression of three SCN light response genes, Dusp4, Rasd1, and Gem. Transcriptional modulation of Dusp4 and Rasd1, and phase regulation of Gem, are compelling candidate molecular mechanisms for plasticity in the SCN light response through their modulation of the critical NMDAR-MAPK/ERK-CREB/CRE light signaling pathway in SCN neurons. Modulation of Prokr2 and Cck may critically support SCN neural network reconfiguration during photoperiodic entrainment. Our findings identify the SCN light response and neuropeptide signaling gene sets as rich substrates for elucidating novel mechanisms of photoperiod plasticity. Data is also available on our corresponding website, where users can search and view the expression and rhythmic properties of genes across these photoperiod conditions.

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Light-induced Changes in the Suprachiasmatic Nucleus Transcriptome Regulated by the ERK/MAPK Pathway

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