title: Shell neurons of the master circadian clock coordinate the phase of tissue clocks throughout the brain and body.
abstract: BACKGROUND
  Daily rhythms in mammals are programmed by a master clock in the suprachiasmatic nucleus (SCN). The SCN contains two main compartments (shell and core), but the role of each region in system-level coordination remains ill defined. Herein, we use a functional assay to investigate how downstream tissues interpret region-specific outputs by using in vivo exposure to long day photoperiods to temporally dissociate the SCN. We then analyze resulting changes in the rhythms of clocks located throughout the brain and body to examine whether they maintain phase synchrony with the SCN shell or core.
  
  
  RESULTS
  Nearly all of the 17 tissues examined in the brain and body maintain phase synchrony with the SCN shell, but not the SCN core, which indicates that downstream oscillators are set by cues controlled specifically by the SCN shell. Interestingly, we also found that SCN dissociation diminished the amplitude of rhythms in core clock gene and protein expression in brain tissues by 50-75 %, which suggests that light-driven changes in the functional organization of the SCN markedly influence the strength of rhythms in downstream tissues.
  
  
  CONCLUSIONS
  Overall, our results reveal that body clocks receive time-of-day cues specifically from the SCN shell, which may be an adaptive design principle that serves to maintain system-level phase relationships in a changing environment. Further, we demonstrate that lighting conditions alter the amplitude of the molecular clock in downstream tissues, which uncovers a new form of plasticity that may contribute to seasonal changes in physiology and behavior.
authors.affiliation: Department of Biomedical Sciences, Marquette University, Milwaukee, WI, 53233, USA. jennifer.evans@marquette.edu.
authors.forename: Jennifer A
authors.initials: JA
authors.lastname: Evans
authors.affiliation: Department of Neurobiology, Morehouse School of Medicine, Atlanta, GA, 30310, USA.
authors.forename: Ting-Chung
authors.initials: TC
authors.lastname: Suen
authors.affiliation: Department of Biomedical Sciences, Marquette University, Milwaukee, WI, 53233, USA.
authors.forename: Ben L
authors.initials: BL
authors.lastname: Callif
authors.affiliation: Department of Neurobiology, Morehouse School of Medicine, Atlanta, GA, 30310, USA.
authors.forename: Andrew S
authors.initials: AS
authors.lastname: Mitchell
authors.affiliation: Department of Neurobiology, Morehouse School of Medicine, Atlanta, GA, 30310, USA.
authors.forename: Oscar
authors.initials: O
authors.lastname: Castanon-Cervantes
authors.affiliation: Department of Biomedical Sciences, Marquette University, Milwaukee, WI, 53233, USA.
authors.forename: Kimberly M
authors.initials: KM
authors.lastname: Baker
authors.affiliation: Department of Biomedical Sciences, Marquette University, Milwaukee, WI, 53233, USA.
authors.forename: Ian
authors.initials: I
authors.lastname: Kloehn
authors.affiliation: Department of Pharmacology, Morehouse School of Medicine, Atlanta, GA, 30310, USA.
authors.forename: Kenkichi
authors.initials: K
authors.lastname: Baba
authors.affiliation: Department of Biology and Center for Obesity Reversal, Georgia State University, Atlanta, GA, 30302, USA.|Department of Developmental Neurobiology, St. Jude Children's Research Hospital, Memphis, TN, 38105, USA.
authors.forename: Brett J W
authors.initials: BJ
authors.lastname: Teubner
authors.affiliation: Department of Neurobiology, Morehouse School of Medicine, Atlanta, GA, 30310, USA.
authors.forename: J Christopher
authors.initials: JC
authors.lastname: Ehlen
authors.affiliation: Department of Neurobiology, Morehouse School of Medicine, Atlanta, GA, 30310, USA.
authors.forename: Ketema N
authors.initials: KN
authors.lastname: Paul
authors.affiliation: Department of Biology and Center for Obesity Reversal, Georgia State University, Atlanta, GA, 30302, USA.
authors.forename: Timothy J
authors.initials: TJ
authors.lastname: Bartness
authors.affiliation: Department of Pharmacology, Morehouse School of Medicine, Atlanta, GA, 30310, USA.
authors.forename: Gianluca
authors.initials: G
authors.lastname: Tosini
authors.affiliation: Department of Mathematics and Statistics, Amherst College, Amherst, MA, 01002, USA.
authors.forename: Tanya
authors.initials: T
authors.lastname: Leise
authors.affiliation: Department of Neurobiology, Morehouse School of Medicine, Atlanta, GA, 30310, USA.
authors.forename: Alec J
authors.initials: AJ
authors.lastname: Davidson
mesh_terms: D000818:Animals; D001921:Brain / Q000166:cytology / Q000502:physiology*; D057906:Circadian Clocks; D002940:Circadian Rhythm; D008027:Light; D008297:Male; D008810:Mice, Inbred C57BL; D009474:Neurons / Q000166:cytology* / Q000502:physiology; D017440:Photoperiod; D013493:Suprachiasmatic Nucleus / Q000166:cytology*