178 — Diurnal transcriptome atlas of a primate across major neural and peripheral tissues

When studying gene expression, time-of-day is an important factor in determining which genes will be expressed in what tissues. (If you looked at mid-morning tissues, you’re unlikely to find any melatonin gene expression, even though we produce plenty in the evening!) Mice are commonly used as the model for circadian rhythms in mammals, but it’s pretty widely acknowledged that this is a pretty bad idea when trying to understand human circadian rhythms because humans are diurnal while mice are nocturnal…humans eat discrete meals during the day whereas mice (especially lab mice) often eat many tiny snacks throughout the day as they get hungry…

While it’s common for papers to posit that the suprachiasmatic nucleus (SCN) circadian oscillator is approximately homologous between mice and humans, most agree that it’s not a very good assumption. But getting better results is expensive both in labor and in infrastructure.

That’s why it’s very exciting that this group established a full “transcriptome” for a primate — namely, a baboon — during a full circadian cycle, polling tissue from the nervous system as well as the circulatory, immune, digestive, and other systems.

Among their findings? The vast majority of gene expression is cyclical, with significant correlation with the time of day. 82.2% of the genes that code for “druggable target proteins” as identified by the FDA undergo rhythmicity, which means that pharmaceutical treatments may be more effective during certain times of the day. And there were enough differences between mouse and baboon expression schedules that it’s pretty clear that researchers should think carefully about the schedules of their particular animal of study.