Timing is Everything, to Our Genes

Source: Salk Institute

Summary: Researchers in a new study found that the activity of nearly 80 percent of genes follows a day/night rhythm in many tissue types and brain regions.

To everything there is a season, this saying applies to many human endeavors and the new research shows it’s even true on the molecular level. Of the 25,000 genes in the primate genome, nearly 11,000 were expressed in all tissues. Of those (which mostly govern routine cellular functions, such as DNA repair and energy metabolism), 96.6% were particularly rhythmic in at least one tissue, varying drastically by when they were sampled. While scientists have long known that many tissues follow these cycles, called circadian rhythms, researchers from the Salk Institute made a most comprehensive study connecting timing to gene transcription (the process of copying DNA into RNA to guide protein assembly). They found that the activity of nearly 80% of genes follows a day/night rhythm in many tissue types and brain regions. The study findings were published in the journal Science.

Genes follows a day/night rhythm in many tissue types

Salk scientists discover critical gene activity follows a biological clock, affecting diseases of the brain and body. Credit: Salk Institute

Using RNA sequencing, the research team tracked gene expression in dozens of different non-human primate tissues every 2 hours for 24 hours. The team found that each tissue contained genes that were expressed at different levels based on the time of day. However, the number of these “rhythmicgenes varied by tissue type, from around 200 in the pineal, mesenteric lymph nodes, bone marrow and other tissues to more than 3,000 in the prefrontal cortex, thyroid, gluteal muscle and others. In addition, genes that were expressed most often tended to show more rhythmicity, or variability by time. The Salk team’s gene expression atlas could also help scientists illuminate how late-night lifestyles impact human health. This molecular timing mechanism could also impact drug effectiveness. In the future, pharmacists may provide patients more detailed instructions on how often and when to take drugs.

Prof. Satchidananda Panda said, “This is a list of how genes are differentially expressed in different organs, and that will give us a framework to understand if shift work and other disruptions change how genes are expressed”, “For earlier circadian rhythm research, we did not have a reference, so this is like having a human reference genome.”

More Information: Ludovic S. Mure et al, “Diurnal transcriptome atlas of a primate across major neural and peripheral tissues”, Science (2018).DOI: 10.1126/science.aao0318 , science.sciencemag.org/content … 2/07/science.aao0318

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