How the daily biological clock starts working during mammal development

The circadian clock oscillation emerges during mid-to-late gestation in mammals.

• Circadian clocks are intrinsic oscillators that coordinate functions within organs and tissues.
• In vitro differentiation of mouse embryonic stem cells mimics the development of circadian clocks.
• Cell reprogramming can lead to the reappearance of circadian clocks.
• Before the circadian clock develops, embryos experience ultradian rhythms controlled by the segmentation clock.
• The emergence of circadian clock oscillation is significant in the context of mammalian development.

Simplified