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Updated: Jun 26, 2026

Monitoring Cell-autonomous Circadian Clock Rhythms of Gene Expression Using Luciferase Bioluminescence Reporters
Published on: September 27, 2012
The molecular mechanism regulating the autonomous circadian expression of Topoisomerase I in NIH3T3 cells
Fang Yang1, Yoshihiro Nakajima, Megumi Kumagai
1Department of Physiology, Saitama Medical University, 38 Morohongo, Moroyama, Iruma-gun, Saitama 350-0495, Japan.
Abstract:
To identify whether Topoisomerase I (TopoI) has autonomous circadian rhythms regulated by clock genes, we tested mouse TopoI (mTopoI) promoter oscillation in NIH3T3 cells using a real-time monitoring assay and TopoI mRNA oscillations using real-time RT-PCR. Analysis of the mTopoI promoter region with Matlnspector software revealed two putative E-box (E1 and E2) and one DBP/E4BP4-binding element (D-box). Luciferase assays indicated that mTopoI gene expression was directly regulated by clock genes. The real-time monitoring assay showed that E-box and D-box response elements participate in the regulation of the circadian expression of mTopoI. Furthermore, a gel-shift assay showed that E2 is a direct target of the BMAL1/CLOCK heterodimer and DBP binds to the putative D-site. These results indicate that TopoI is expressed in an autonomous circadian rhythm in NIH3T3 cells.
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