Combined Pharmacological and Genetic Manipulations Unlock Unprecedented Temporal Elasticity and Reveal Phase-Specific Modulation of the Molecular Circadian Clock of the Mouse Suprachiasmatic Nucleus.
The suprachiasmatic nucleus (SCN) is the master circadian oscillator encoding time-of-day information. SCN timekeeping is sustained by a cell-autonomous transcriptional-translational feedback loop, whereby expression of the Period and Cryptochrome genes is negatively regulated by their protein products. This loop in turn drives circadian oscillations in gene expression that direct SCN electrical activity and thence behavior. The robustness of SCN timekeeping is further enhanced by interneuronal, circuit-level coupling. The aim of this study was to combine pharmacological and genetic manipulations to push the SCN clockwork toward its limits and, by doing so, probe cell-autonomous and emergent, circuit-level properties. Circadian oscillation of mouse SCN organotypic slice cultures was monitored as PER2::LUC bioluminescence. SCN of three genetic backgrounds-wild-type, short-period CK1ε(Tau/Tau) mutant, and long-period Fbxl3(Afh/Afh) mutant-all responded reversibly to pharmacological manipulation with period-altering compounds: picrotoxin, PF-670462 (4-[1-Cyclohexyl-4-(4-fluorophenyl)-1H-imidazol-5-yl]-2-pyrimidinamine dihydrochloride), and KNK437 (N-Formyl-3,4-methylenedioxy-benzylidine-gamma-butyrolactam). This revealed a remarkably wide operating range of sustained periods extending across 25 h, from ≤17 h to >42 h. Moreover, this range was maintained at network and single-cell levels. Development of a new technique for formal analysis of circadian waveform, first derivative analysis (FDA), revealed internal phase patterning to the circadian oscillation at these extreme periods and differential phase sensitivity of the SCN to genetic and pharmacological manipulations. For example, FDA of the CK1ε(Tau/Tau) mutant SCN treated with the CK1ε-specific inhibitor PF-4800567 (3-[(3-Chlorophenoxy)methyl]-1-(tetrahydro-2H-pyran-4-yl)-1H-pyrazolo[3,4-d]pyrimidin-4-amine hydrochloride) revealed that period acceleration in the mutant is due to inappropriately phased activity of the CK1ε isoform. In conclusion, extreme period manipulation reveals unprecedented elasticity and temporal structure of the SCN circadian oscillation.



The master circadian clock of the suprachiasmatic nucleus (SCN) encodes time-of-day information that allows mammals to predict and thereby adapt to daily environmental cycles. Using combined genetic and pharmacological interventions, we assessed the temporal elasticity of the SCN network. Despite having evolved to generate a 24 h circadian period, we show that the molecular clock is surprisingly elastic, able to reversibly sustain coherent periods between ≤17 and >42 h at the levels of individual cells and the overall circuit. Using quantitative techniques to analyze these extreme periodicities, we reveal that the oscillator progresses as a sequence of distinct stages. These findings reveal new properties of how the SCN functions as a network and should inform biological and mathematical analyses of circadian timekeeping.
Division of Neurobiology, Laboratory of Molecular Biology, Medical Research Council, Cambridge CB2 0QH, United Kingdom.
Andrew P
0000-0003-2666-4254
AP
Patton
Division of Neurobiology, Laboratory of Molecular Biology, Medical Research Council, Cambridge CB2 0QH, United Kingdom.
Johanna E
0000-0002-8981-2667
JE
Chesham
Division of Neurobiology, Laboratory of Molecular Biology, Medical Research Council, Cambridge CB2 0QH, United Kingdom mha@mrc-lmb.cam.ac.uk.
Michael H
0000-0001-8576-6651
MH
Hastings
D000818:Animals; D000831:Animals, Newborn; D001559:Benzhydryl Compounds / Q000494:pharmacology; D002940:Circadian Rhythm / Q000187:drug effects* / Q000235:genetics*; D004791:Enzyme Inhibitors / Q000494:pharmacology; D005071:Evoked Potentials / Q000187:drug effects / Q000235:genetics; D044783:F-Box Proteins / Q000235:genetics / Q000378:metabolism; D018756:GABA Antagonists / Q000494:pharmacology; D066298:In Vitro Techniques; D051379:Mice; D008822:Mice, Transgenic; D009924:Organ Culture Techniques; D056950:Period Circadian Proteins / Q000235:genetics / Q000378:metabolism*; D011743:Pyrimidines / Q000494:pharmacology; D011760:Pyrrolidinones / Q000494:pharmacology; D026941:Sodium Channel Blockers / Q000494:pharmacology; D013493:Suprachiasmatic Nucleus / Q000166:cytology / Q000187:drug effects* / Q000502:physiology*; D013779:Tetrodotoxin / Q000494:pharmacology; D013997:Time Factors; D016875:tau Proteins / Q000235:genetics*
D001559:Benzhydryl Compounds; D004791:Enzyme Inhibitors; D044783:F-Box Proteins; C519795:FBXL3 protein, human; D018756:GABA Antagonists; C410027:KNK 437; C421902:PER2 protein, human; D056950:Period Circadian Proteins; D011743:Pyrimidines; D011760:Pyrrolidinones; D026941:Sodium Channel Blockers; D016875:tau Proteins; D013779:Tetrodotoxin; C522839:PF-670462
FBXL3; bioluminescence; casein kinase; organotypic slice; period; picrotoxin