Identification of novel light-induced genes in the suprachiasmatic nucleus - PubMed (original) (raw)
Identification of novel light-induced genes in the suprachiasmatic nucleus
Veronica M Porterfield et al. BMC Neurosci. 2007.
Abstract
Background: The transmission of information about the photic environment to the circadian clock involves a complex array of neurotransmitters, receptors, and second messenger systems. Exposure of an animal to light during the subjective night initiates rapid transcription of a number of immediate-early genes in the suprachiasmatic nucleus of the hypothalamus. Some of these genes have known roles in entraining the circadian clock, while others have unknown functions. Using laser capture microscopy, microarray analysis, and quantitative real-time PCR, we performed a comprehensive screen for changes in gene expression immediately following a 30 minute light pulse in suprachiasmatic nucleus of mice.
Results: The results of the microarray screen successfully identified previously known light-induced genes as well as several novel genes that may be important in the circadian clock. Newly identified light-induced genes include early growth response 2, proviral integration site 3, growth-arrest and DNA-damage-inducible 45 beta, and TCDD-inducible poly(ADP-ribose) polymerase. Comparative analysis of promoter sequences revealed the presence of evolutionarily conserved CRE and associated TATA box elements in most of the light-induced genes, while other core clock genes generally lack this combination of promoter elements.
Conclusion: The photic signalling cascade in the suprachiasmatic nucleus activates an array of immediate-early genes, most of which have unknown functions in the circadian clock. Detected evolutionary conservation of CRE and TATA box elements in promoters of light-induced genes suggest that the functional role of these elements has likely remained the same over evolutionary time across mammalian orders.
Figures
Figure 1
Laser capture and gene expression in response to a light pulse. (a) Twelve μm thick coronal section containing the SCN, indicated by arrows. Sections are stained with hemotoxylin. (b) The same section after capture, showing the removal of the paired SCN.
Figure 2
Gene expression after light pulse vs. sham light pulse. Summary comparison of gene expression after a light pulse vs. control dark pulse. Each point represents one gene that was present on at least half of the arrays. The boxes indicate data points that were subsequently confirmed as significantly different between conditions by qPCR.
Figure 3
Fold change of light-induced genes, measured by qPCR. Fold change following a light pulse of genes significantly upregulated following the light pulse as compared to the sham light pulse, as measured by qPCR. Error bars represent 95% confidence intervals.
Figure 4
Conserved promoter elements in light-induced genes. Conserved CRE and TATA-box elements in promoter regions of four immediate-early genes in five mammalian genomes: (A) Egr1, (B) Fos, (C) Per1 and (D) Klf4. Translational start codon ATG begins at +1. Alignment gaps are shown as dashes (-), dots (.) indicate identity to the first sequence. For Klf4, genomic sequence of dog was not available. Predicted conserved CRE elements are outlined with shaded boxes; putative TATA-boxes are shown with white boxes.
References
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