Collaboration Uncovers New Insights into the Structure of Circadian mRNA Period2

Thursday - November 9 2023, 02:26 UTC - 1 year ago

A collaborative study from Osaka University, the University of Tokyo, and the Queensland University of Technology has recently revealed a structure in the circadian mRNA Period2 that affects the sleep-wake cycle, particularly during the early morning and late evening. The research concerned the role of post-transcriptional processes in the body’s internal clock and sleep patterns, showing how the 5' untranslated region of mRNA can affect total sleep duration.

A collaborative study involving scientists from Osaka University, the University of Tokyo, and the Queensland University of Technology has identified a structure in the circadian mRNA Period2 that affects the sleep-wake cycle, particularly during the early morning and late evening.

Circadian rhythms are the internal biological clocks that orchestrate our daily activities, playing a vital role in health and well-being. The role of transcription in regulating these rhythms is well-established.

However, a recent study published in the journal Proceedings of the National Academy of Sciences has revealed new insights into the importance of post-transcriptional processes. The research redefines our understanding by highlighting how translation and post-transcriptional processes affect the body’s internal clock and sleep patterns.

By using ribosome profiling, the research team examined the timing of ribosome binding in relation to peak protein and RNA levels. They discovered significant differences in the timing of these processes, suggesting a complex post-translational control of circadian protein production.

"We built upon our previous work to precisely quantify the level of circadian proteins in mice held in constant darkness over a 24-hour period, which controls for the confounding effects of light," says corresponding author Hiroki Ueda. "Using ribosome profiling, I wanted to see how the binding of ribosomes to RNA related to the timing of when those proteins actually got made. And by trying to answer this basic timing question, we found that ribosomes bind an upstream open reading frame in Period2 which altered the amplitude of circadian rhythms and disrupted sleep in mice," adds lead author Arthur Millius.

The researchers found many upstream open reading frames (uORFs) in the 5’ untranslated region of circadian mRNAs, which is the part of RNA before the so-called "coding sequence" that gets translated by ribosomes into protein. These uORFs were associated with reduced ribosome binding in the main coding sequence and reduced reporter expression in a variety of circadian assays tested by the researchers suggesting a role for uORFs in shaping circadian protein expression.

"About half of genes in mice and humans have at least one uORF," explains Dimitri Perrin, the team’s bioinformatician, "but it’s particularly interesting that about 75% of genes associated with circadian rhythms have an uORF, which means that circadian rhythms are particularly susceptible to this type of post-transcriptional regulation." .

Mutating the uORF in the core clock gene Period2 (Per2) yielded intriguing results. It boosted Per2 mRNA expression while significantly reducing total sleep duration in mice, particularly during transitions between light and dark. "Our sleep data suggests that disrupting uORFs can have physiological impacts on mice behavior, which shows that you don’t have to mutate the protein to have an effect," explains Rikuhiro Yamada who analyzed the phenotype of the mice using the lab’s snappy sleep stager system.

"We performed ribosome profiling on the Per2 uORF mutant mice, and although ribosome binding was e­levated to the main ORF, it was not sufficient to increase the protein levels to the wild type. This is likely because when the uORF is mutated and Per2 mRNA is boosted, the ribosomes end up searching for other targets before they reach the main ORF," said Yamada.

A recently published study conducted by collaborative research teams from Osaka University, the University of Tokyo, and the Queensland University of Technology has brought to light a structure in the circadian mRNA (molecules responsible for the sleep-wake cycle) Period2 that shapes the body’s circadian clock. Utilising ribosome profiling, the innovative research team analysed the timing of different RNA and protein levels, discovering a powerful post-transcriptional control of circadian protein production. Through the analysis of the upstream open reading frames from circadian mRNAs and the mutation of the core clock gene Period2, the research team was able to reveal that disrupting the '5' untranslated region of mRNA has physiological significance as evidenced by reduced total sleep duration in mice, particularly during transitions between light and dark. This novel information about the importance of the post-transcriptional process and its affect on sleep gives scientists a better understanding of circadian rhythm dynamics.