Non-circadian expression masking clock-driven weak transcription rhythms in U2OS cells

Area of Science:

• Cellular Biology
• Chronobiology
• Genomics

Background:

• U2OS cells possess a circadian clock.
• However, they exhibit limited rhythmic gene expression under constant conditions.

Purpose of the Study:

• To investigate the extent of circadian gene regulation in U2OS cells.
• To understand the interplay between circadian and non-circadian transcription.

Main Methods:

• Identified binding sites of circadian regulators (BMAL1, CLOCK, CRY1) using genome-wide analysis.
• Utilized luciferase fusions to assess promoter activity.
• Analyzed transcript levels under constant conditions.

Main Results:

• Discovered 3040 binding sites for BMAL1, CLOCK, and CRY1.
• Found minimal correlation between binding sites and rhythmic transcript levels.
• Demonstrated that robust, low-amplitude circadian transcription is masked by dominant non-circadian transcription.

Conclusions:

• U2OS cells have a weak intrinsic circadian oscillator.
• The circadian clock has the potential to regulate numerous genes.
• Metabolic state influences the balance of circadian versus non-circadian transcription, affecting transcriptome complexity.