Circadian key component CLOCK/BMAL1 interferes with segmentation clock in mouse embryonic organoids.

In mammals, circadian clocks are strictly suppressed during early embryonic stages, as well as in pluripotent stem cells, by the lack of CLOCK/BMAL1-mediated circadian feedback loops. During ontogenesis, the innate circadian clocks emerge gradually at a late developmental stage, and with these, the circadian temporal order is invested in each cell level throughout a body. Meanwhile, in the early developmental stage, a segmented body plan is essential for an intact developmental process, and somitogenesis is controlled by another cell-autonomous oscillator, the segmentation clock, in the posterior presomitic mesoderm (PSM). In the present study, focusing upon the interaction between circadian key components and the segmentation clock, we investigated the effect of the CLOCK/BMAL1 on the segmentation clock Hes7 oscillation, revealing that the expression of functional CLOCK/BMAL1 severely interferes with the ultradian rhythm of segmentation clock in induced PSM and gastruloids. RNA sequencing analysis implied that the premature expression of CLOCK/BMAL1 affects the Hes7 transcription and its regulatory pathways. These results suggest that the suppression of CLOCK/BMAL1-mediated transcriptional regulation during the somitogenesis may be inevitable for intact mammalian development.