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The Journal of Neuroscience, October 15, 2001, 21(20):7937-7943
Oscillating on Borrowed Time: Diffusible Signals from
Immortalized Suprachiasmatic Nucleus Cells Regulate Circadian
Rhythmicity in Cultured Fibroblasts
Gregg
Allen1,
Jodie
Rappe2,
David J.
Earnest1, and
Vincent M.
Cassone2
1 Department of Human Anatomy and Medical Neurobiology,
Texas A&M University Health Science Center, College of Medicine,
College Station, Texas 77843-1114, and 2 Department of
Biology, Texas A&M University, College Station, Texas 77843-3258
The capacity to generate circadian rhythms endogenously and to
confer this rhythmicity to other cells was compared in immortalized cells derived from the suprachiasmatic nucleus (SCN) and a fibroblast line to differentiate SCN pacemaker properties from the oscillatory behavior of non-clock tissues. Only SCN2.2 cells were capable of
endogenously generating circadian rhythms in 2-deoxyglucose uptake and
Per gene expression. Similar to SCN function in
vivo, SCN2.2 cells imposed rhythms of metabolic activity and
Per gene expression on cocultured NIH/3T3 fibroblasts
via a diffusible signal. The conferred rhythms in NIH/3T3 cells were
phase delayed by 4-12 hr relative to SCN2.2 circadian patterns, thus
resembling the phase relationship between SCN and peripheral tissue
rhythms in vivo. Sustained metabolic rhythmicity in
NIH/3T3 cells was dependent on continued exposure to SCN2.2-specific
outputs. In response to a serum shock the NIH/3T3 fibroblasts exhibited
recurrent oscillations in clock gene expression, but not in metabolic
activity. These molecular rhythms in serum-shocked fibroblasts cycled
in a phase relationship similar to that observed in the SCN in
vivo; peak Per1 and Per2 mRNA
expression preceded the rhythmic maxima in Cry1 and
Cry2 mRNA levels by 4 hr. Despite these clock gene oscillations the serum-shocked NIH/3T3 cells failed to drive circadian rhythms of Per1 and Per2 expression in
cocultures of untreated fibroblasts, suggesting that expression and
circadian regulation of the Per and Cry
genes are not sufficient to confer pacemaker function. Therefore,
SCN-specific outputs are necessary to drive circadian rhythms of
metabolic activity, and these output signals are not a direct product
of clock gene oscillations.
Key words:
circadian pacemaker; Clock; oscillation; suprachiasmatic nucleus; glucose use; Per1; Per2; Cry1; Cry2; coculture
Copyright © 2001 Society for Neuroscience 0270-6474/01/21207937-07$05.00/0
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