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|Title:||CIRCADIAN REGULATION OF THE TWO ISOFORMS OF THE ORPHAN NUCLEAR RECEPTOR RORGAMMA|
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|Authors/Affiliations:||1 Valérie Mongrain*; 1 Xuan Ruan; 1 Hugues Dardente; 1 Nicolas Cermakian; |
1 Douglas Mental Health University Institute, Montreal, QC, Canada
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|Content:||Introduction: Circadian clocks control various aspects of physiology and behaviour. It was originally thought that the molecular clockwork was identical in all tissues. However, recent work has identified tissue-specificity and our previous work suggests that nuclear receptors of the ROR family may differentially regulate Bmal1 in a tissue-specific manner. This study aims to compare the expression of RORgamma isoforms and to define the mechanisms behind their tissue-specific expression.|
Methods: The tissue-specific expression of the two RORgamma isoforms in peripheral tissues was assessed in wild-type and Clock mutant mice at ZT2, 8, 14 and 20 using quantitative PCR. The regulation of RORgamma isoforms through elements present in their promoters was studied using luciferase assays in COS7 cells.
Results: In wild-type animals, the expression of RORgamma in the liver peaked at ZT20, while the expression was not rhythmic in muscle, testis and thymus. The expression of RORgammaT was detected at low levels in liver, muscle and testis and at high constant levels in thymus. In mice with a mutant CLOCK protein, the expression of RORgamma was no longer rhythmic in liver and was expressed at higher levels in muscle. The mutation had no effect on RORgammaT expression. Luciferase assay showed that CLOCK/BMAL1 induced the transcription of RORgamma via its E-boxes, whereas it did not activate transcription via RORgammaT E-box. Lastly, we observed that both RORgamma and RORgammaT could activate the promoter of RORgamma.
Conclusions: These results give insights into the molecular mechanisms that can lead to differential expression, among isoforms and between tissues, of a single gene.
Support : Research supported by NSERC.
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