2016 Fiscal Year Annual Research Report
Chronic effects of non-24 hour solar days
Publicly Offered Research
| Project Area | "LIVING IN SPACE" - Integral Understanding of life-regulation mechanism from "SPACE" |
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| Project/Area Number |
16H01652
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| Research Institution | Okinawa Institute of Science and Technology Graduate University |
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Principal Investigator |
Myung Jihwan 沖縄科学技術大学院大学, 計算脳科学ユニット, 客員研究員 (80643204)
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| Project Period (FY) |
2016-04-01 – 2018-03-31
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| Keywords | Circadian rhythms / Solar day / Synchronization / Suprachiasmatic nucleus / Phase oscillator / Neural network / Phase-repulsive coupling / Photoperiodism |
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| Outline of Annual Research Achievements |
We investigate how extra-terrestrial solar days (non-24-h days) reorganize component circadian clocks in the suprachiasmatic nucleus (SCN), the master circadian clock of the brain (Azzi et al, Neuron, 2017). The solar day reorganization is mediated by the neural network connection in the SCN, as blockade of GABA signaling abolishes the phenotypes. We apply the asymmetric coupling model for the photoperiodic encoding (Myung et al, PNAS, 2015) and find it equally applicable to solar day adaptation. While the dynamical properties in the SCN culture can be described by temporal phase relations, the system as a whole can be seen as a generator of spatial patterns. Therefore, we introduce a new quantitative measure for spatiotemporal patterns, called Moran’s I (Schmal et al, Bioinformatics, accepted).
The intra-SCN dynamics is a bridge to understand the brain-wide dynamics. The circadian oscillators in the brain similarly reorganize their relative phases under summer days, which we have found to be equivalent to the long solar days. To understand how this reorganization influences the overall in vivo dynamics, we generated CP-specific Bmal1 KO mice (FOXJ1-Cre;Bmal1flx/flx). These mice lack circadian clocks in their CPs and show lengthened circadian period under constant darkness. This in vivo phenotype can be reproduced in vitro, through co-culture of the SCN and the CP. This is compelling evidence that internal disorganization of circadian clocks has direct consequences in vivo and provides a first clue to understand the brain endophenotype under chronic non-24-h solar days.
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| Current Status of Research Progress |
Current Status of Research Progress
2: Research has progressed on the whole more than it was originally planned.
Reason
One paper on solar day entrainment of the SCN has been successfully published in Neuron as a collaboration project [1]. And a second paper focusing on methods is accepted in May 2017 [2].
[1] Azzi A, Evans JA, Leise T, Myung J, Takumi T, Davidson AJ, Brown SA (2017). Network dynamics mediate circadian clock plasticity. Neuron. 93:441-450.
[2] Schmal C, Myung J, Herzel H, Bordyugov G (2017). Moran’s I quantifies spatio-temporal pattern formation in neural imaging data. Bioinformatics. (accepted)
In addition, two more papers are close to submission.
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| Strategy for Future Research Activity |
Our studies in the previous financial year show that the clock in the mammalian brain has a networked structure and the network enables the clock to adapt to the non-Earth, non-24 hour cycles. It now remains to be seen how the clock adaptation affects the physiology of the whole brain. We plan to continue computational analysis and modeling of our experimental data to summarize our results and publish two upcoming manuscripts in the next financial year. We are extending our findings in the SCN to the whole brain with the aim of interpreting them in the context of the predictive homeostasis under a pattern of day-night cycles.
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