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Circadian Profiling of the Transcriptome in Immortalized Rat SCN Cells: Comparison to Long-Evans Rat SCN

ABSTRACT: To determine whether immortalized cells derived from the rat SCN (SCN 2.2) retain intrinsic rhythm-generating properties characteristic of the SCN, oscillatory properties of the SCN2.2 transcriptome were analyzed and compared to those found in the rat SCN in vivo using rat U34A Affymetrix GeneChips. In this comparison, adult male Long-Evans rats (175-200g; N=45) were housed under a standard 12h light:12h dark photoperiod (LD 12:12; lights-on at 0600 hr). At 1800 hr (circadian time [CT] 12), animals were exposed to constant darkness (DD) and 12 hours later (0600 hr or CT 0), sacrificed under isoflurane anesthesia at 6-hr intervals (N=5) for 48 hours by decapitation using an infrared viewer. After the eyes were removed in the dark, SCN tissue was immediately dissected under dim light, frozen in liquid nitrogen, and stored at –800C. SCN tissue from individual animals was separately homogenized in TRIzol reagent by aspiration through a 25-gauge needle and then extracted cellular RNA for all animals at each timepoint was pooled into a single sample. RNA samples were subjected to on-column treatment with DNAse-1 to digest genomic DNA and then were stored at –80°C before routine processing for GeneChip analysis. Keywords: other

ORGANISM(S): Rattus norvegicus

PROVIDER: GSE1673 | GEO | 2004/10/09

SECONDARY ACCESSION(S): PRJNA104749

REPOSITORIES: GEO

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Project description:To screen for specific circadian outputs that may distinguish the pacemaker in the mammalian suprachiasmatic nucleus (SCN) from peripheral-type oscillators in which the canonical clockworks are similarly regulated in a circadian manner, the rhythmic behavior of the transcriptome in forskolin-stimulated NIH/3T3 fibroblasts was analyzed and compared to that found in the rat SCN in vivo and SCN2.2 cells in vitro. Similar to the scope of circadian gene expression in SCN2.2 cells and the rat SCN, NIH/3T3 fibroblasts exhibited circadian fluctuations in the expression of the core clock genes, Per2, Bmal1 (Mop3), and Cry1 and 323 functionally diverse transcripts (2.6%), many of which were involved in cell communication. Overlap in rhythmically-expressed transcripts among NIH/3T3 fibroblasts, SCN2.2 cells and the rat SCN was limited to these clock genes and four other genes that mediate fatty acid and lipid metabolism or function as nuclear factors. Compared to NIH/3T3 cells, circadian gene expression in SCN oscillators was more prevalent among cellular pathways mediating glucose metabolism and neurotransmission. Coupled with evidence for the rhythmic regulation of the inducible isoform of nitric oxide synthase, the enzyme responsible for the production of nitric oxide, in SCN2.2 cells and the rat SCN but not in fibroblasts, studies examining the effects of a NOS inhibitor on metabolic rhythms in co-cultures containing SCN2.2 cells and untreated NIH/3T3 cells suggest that this gaseous neurotransmitter may play a key role in SCN pacemaker function. Thus, this comparative analysis of circadian gene expression in SCN and non-SCN cells may have important implications in the selective identification of circadian signals involved in the coupling of SCN oscillators and the regulation of rhythmicity in downstream cells or tissues. Experiment Overall Design: Circadian profiling of the NIH/3T3 fibroblast transcriptome entailed the treatment of NIH/3T3 cells with a 15uM forskolin pulse, subsequent washout of the drug, and collection of total RNA immediately after washout and every 6 hours across two circadian cycles for each of three experiments. Timepoint values reflect the average of three samples from these biological replicates.

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Circadian Profiling of the Transcriptome in Immortalized Rat SCN Cells: Comparison to Long-Evans Rat SCN

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