What's the science?
Gene expression is critical for regulating every process in the human body, but how does gene expression change in real-time throughout the day? Previous studies of gene expression throughout the day have been in mice, who are nocturnal animals. Currently, we don’t understand how gene expression fluctuates in animals who are awake during the day, like humans. This week in Science, Mure and colleagues examine gene expression over 24 hours in baboons who share a similar sleep-wake cycle to humans.
How did they do it?
Gene expression was measured using RNA-sequencing, a technique for counting the number of transcripts (copy of DNA carrying information for protein production) produced by genes. The authors measured gene expression in the baboon every two hours in 64 different tissues over a 24-hour period. This 24-hour period contained 12 hours of light and 12 hours of dark and a fixed eating schedule. Sleep and behavior were monitored. Tissues examined for gene expression were several important brain regions and organs.
What did they find?
All tissues showed some level of rhythmic gene expression (i.e. transcripts that were produced cyclically throughout the day). The number of rhythmic transcripts varied a lot between tissues (for example 200 in the pineal gland to > 3000 in the prefrontal cortex) and there was little overlap between these rhythmic transcripts in different tissues. More than 10,000 transcripts detected were common to all tissues (i.e. “ubiquitously expressed genes”). These genes were involved in core processes such as protein regulation and DNA repair and the majority of rhythmic transcripts found across all tissues were from this set of genes. Gene expression was organized into bursts of expression that occurred in the early morning and again in the late afternoon, while expression was reduced in the evening before sleep when food intake was low.
What's the impact?
Understanding gene expression patterns is important for understanding human behavior. This is the first study to show that gene expression is rhythmic and cycles throughout the day in a species that shows a similar gene expression profile to humans. Understanding which genes are rhythmic will be important when targeting these genes for therapy in various diseases.
L. Mure et al., Diurnal transcriptome atlas of a primate across major neural and peripheral tissues. Science (2018). Access the original scientific publication here.