miR-455-5p regulates circadian rhythms by accelerating the degradation of Clock mRNA

Area of Science:

• Molecular Biology
• Chronobiology
• Genetics

Background:

• Circadian rhythms are endogenous biological processes synchronized with the 24-hour day-night cycle.
• Core circadian rhythmicity is maintained by transcription-translation feedback loops (TTFLs) involving proteins like CLOCK, BMAL1, PER, and CRY.
• The precise roles of microRNAs (miRNAs) in regulating circadian rhythms are not fully understood.

Purpose of the Study:

• To investigate the role of microRNAs in regulating circadian rhythms.
• To elucidate the regulatory mechanism of miR-455 in the context of circadian clock function.
• To determine if a feedback loop exists between CLOCK protein, Clock mRNA, and miR-455.

Main Methods:

• miRNA sequencing (miRNA-seq) was employed to screen for miRNAs involved in circadian regulation.
• Bioluminescence assays using Per2::Luc U2OS cells were performed to monitor circadian rhythm dynamics in real-time.
• Luciferase reporter assays and mRNA stability assays were used to confirm the interaction between miR-455-5p and Clock mRNA.

Main Results:

• The expression of miR-455 was found to be regulated by the CLOCK protein.
• miR-455-5p directly binds to the 3' untranslated region (3'UTR) of Clock mRNA, influencing its stability.
• Overexpression of miR-455-5p was shown to lengthen the period and decrease the amplitude of circadian rhythms in synchronized cells, while its inhibition had the opposite effect.
• miR-455-5p was identified as a modulator of the circadian clock, contributing to fine-tuning circadian rhythms in vitro.

Conclusions:

• miR-455-5p plays a crucial role in maintaining normal circadian rhythmicity by regulating Clock mRNA stability.
• A novel feedback mechanism involving CLOCK protein, Clock mRNA, and miR-455-5p has been identified.
• This regulatory axis is essential for cellular circadian rhythm maintenance and fine-tuning.