Diverse forms of life have evolved 24-hour or circadian timekeeping systems
serving to coordinate internal biological events with the daily solar cycle. The generation
of circadian rhythms by this timekeeping system ensures that internal processes occur at
the appropriate time of day or night in relation to the environmental cycle and to other
functionally-affiliated events. For mammals, endogenous oscillations in gene expression
are a prevalent feature of oscillatory cells residing in the suprachiasmatic nucleus (SCN)
and non-SCN tissues. To determine whether immortalized cells derived from the rat SCN
(SCN2.2) retain the intrinsic rhythm-generating properties of the SCN, oscillatory
behavior of the SCN2.2 transcriptome was analyzed and compared to that found in the rat
SCN in vivo. In SCN2.2 cells, 116 unique genes and 46 ESTs or genes of unknown
function exhibited circadian fluctuations for 2 cycles. Many (35%) of these rhythmicallyregulated
genes in SCN2.2 cells also exhibited circadian profiles of mRNA expression in
the rat SCN in vivo. To screen for output signals that may distinguish oscillatory cells in
the mammalian SCN from peripheral-type oscillators, the rhythmic behavior of the
transcriptome in forskolin-stimulated NIH/3T3 fibroblasts was analyzed and compared
relative to SCN2.2 cells in vitro and the rat SCN in vivo. Similar to the circadian profiling of the SCN2.2 and rat SCN transcriptomes, NIH/3T3 fibroblasts exhibited rhythmic
fluctuations in the expression of the core clock genes and 323 (2.6%) functionally diverse
transcripts. Overlap in rhythmically expressed transcripts among these different oscillator
models was limited to the clock genes and four genes that function in metabolism or
transcription. Coupled with evidence for the rhythmic regulation of the inducible isoform
of nitric oxide synthase (Nos) in SCN2.2 cells and the rat SCN but not in fibroblasts,
studies examining the effects of antisense oligonucleotide-mediated inhibition of Nos2
suggest that the gaseous neurotransmitter nitric oxide may play a key role in SCN
pacemaker function. Thus, our comparative analysis of circadian gene expression in SCN
and non-SCN cells has important implications in the selective analysis of circadian
signals involved in the coupling of SCN oscillators and regulation of rhythmicity in
downstream cells.
| Identifer | oai:union.ndltd.org:tamu.edu/oai:repository.tamu.edu:1969.1/ETD-TAMU-1244 |
| Date | 15 May 2009 |
| Creators | Menger, Gus John, III |
| Contributors | Earnest, David J. |
| Source Sets | Texas A and M University |
| Language | en_US |
| Detected Language | English |
| Type | Book, Thesis, Electronic Dissertation, text |
| Format | electronic, application/pdf, born digital |
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