A cellular basis for the mammalian nocturnal-diurnal switch

Area of Science:

• Evolutionary Biology
• Chronobiology
• Cellular Signaling

Background:

• Early mammals were primarily nocturnal, while dinosaurs occupied diurnal niches.
• The transition of mammals to diurnal activity post-Cretaceous-Paleogene extinction lacks clear mechanistic explanations.
• Understanding the cellular basis of temporal niche selection is crucial for evolutionary studies.

Purpose of the Study:

• To identify the cell-intrinsic mechanisms underlying the mammalian shift from nocturnal to diurnal activity.
• To investigate the role of thermodynamic properties in cellular clocks during this evolutionary transition.
• To explore the genetic and signaling pathways involved in regulating diurnal versus nocturnal behavior.

Main Methods:

• Comparative genomics to identify accelerated evolution in signaling pathways.
• Analysis of protein synthesis, phosphorylation, and circadian timing sensitivity to temperature in cells from diurnal and nocturnal mammals.
• Pharmacological inhibition of the mechanistic target of rapamycin (mTOR) pathway in nocturnal mice.

Main Results:

• Cells from diurnal mammals exhibit reduced sensitivity of protein synthesis, phosphorylation, and circadian timing to temperature fluctuations compared to nocturnal mammals.
• Comparative genomics revealed accelerated evolution in key signaling pathways, notably mTOR, enhancing cellular clock robustness.
• Inhibition of mTOR in nocturnal mice induced a shift towards diurnal activity at cellular, tissue, and behavioral levels.

Conclusions:

• A conserved, cell-intrinsic thermodynamic mechanism involving temperature-robust cellular clocks facilitated the mammalian shift to diurnal activity.
• Accelerated evolution in signaling pathways like mTOR provides a genetic and biochemical basis for adapting temporal niches.
• Cellular signaling networks play a critical role in encoding complex phenotypes such as temporal niche selection.