title: A diversity of paracrine signals sustains molecular circadian cycling in suprachiasmatic nucleus circuits.
abstract: The suprachiasmatic nucleus (SCN) is the principal circadian pacemaker of mammals, coordinating daily rhythms of behavior and metabolism. Circadian timekeeping in SCN neurons revolves around transcriptional/posttranslational feedback loops, in which Period (Per) and Cryptochrome (Cry) genes are negatively regulated by their protein products. Recent studies have revealed, however, that these "core loops" also rely upon cytosolic and circuit-level properties for sustained oscillation. To characterize interneuronal signals responsible for robust pacemaking in SCN cells and circuits, we have developed a unique coculture technique using wild-type (WT) "graft" SCN to drive pacemaking (reported by PER2::LUCIFERASE bioluminescence) in "host" SCN deficient either in elements of neuropeptidergic signaling or in elements of the core feedback loop. We demonstrate that paracrine signaling is sufficient to restore cellular synchrony and amplitude of pacemaking in SCN circuits lacking vasoactive intestinal peptide (VIP). By using grafts with mutant circadian periods we show that pacemaking in the host SCN is specified by the genotype of the graft, confirming graft-derived factors as determinants of the host rhythm. By combining pharmacological with genetic manipulations, we show that a hierarchy of neuropeptidergic signals underpins this paracrine regulation, with a preeminent role for VIP augmented by contributions from arginine vasopressin (AVP) and gastrin-releasing peptide (GRP). Finally, we show that interneuronal signaling is sufficiently powerful to maintain circadian pacemaking in arrhythmic Cry-null SCN, deficient in essential elements of the transcriptional negative feedback loops. Thus, a hierarchy of paracrine neuropeptidergic signals determines cell- and circuit-level circadian pacemaking in the SCN.
authors.affiliation: Division of Neurobiology, Medical Research Council Laboratory of Molecular Biology, Cambridge CB2 0QH, United Kingdom. emaywood@mrc-lmb.cam.ac.uk
authors.forename: Elizabeth S
authors.initials: ES
authors.lastname: Maywood
authors.forename: Johanna E
authors.initials: JE
authors.lastname: Chesham
authors.forename: John A
authors.initials: JA
authors.lastname: O'Brien
authors.forename: Michael H
authors.initials: MH
authors.lastname: Hastings
mesh_terms: D000818:Animals; D002940:Circadian Rhythm / Q000235:genetics / Q000502:physiology*; D018920:Coculture Techniques; D056931:Cryptochromes / Q000172:deficiency / Q000378:metabolism; D005786:Gene Expression Regulation; D051379:Mice; D009415:Nerve Net / Q000378:metabolism*; D019899:Paracrine Communication / Q000235:genetics; D051239:Receptors, Vasoactive Intestinal Peptide, Type II / Q000172:deficiency / Q000378:metabolism; D015398:Signal Transduction / Q000235:genetics; D013493:Suprachiasmatic Nucleus / Q000166:cytology / Q000378:metabolism*; D014660:Vasoactive Intestinal Peptide / Q000172:deficiency / Q000378:metabolism
chemical_list: C538964:Cry1 protein, mouse; C538967:Cry2 protein, mouse; D056931:Cryptochromes; D051239:Receptors, Vasoactive Intestinal Peptide, Type II; D014660:Vasoactive Intestinal Peptide