Post-transcriptional regulation of Clock instructs the emergence of robust circadian clock oscillation during mouse development

Circadian clock oscillation emerges in mouse embryo in the later developmental stages. Although circadian clock development is closely correlated with cellular differentiation, the mechanisms of its emergence during mammalian development are not well understood. Here, we demonstrate an essential role of the post-transcriptional regulation of Clock subsequent to the cellular differentiation for the emergence of robust circadian clock oscillation in mouse fetal hearts and mESCs (mouse embryonic stem cells). In mouse fetal hearts, no apparent oscillation of cell-autonomous molecular clock was detectable in around embryonic day (E) 10 whereas robust oscillation was clearly visible in E18 heart. Temporal RNA-seq analysis using mouse fetal hearts reveals much fewer rhythmic genes in E10-12 hearts (63, no clock genes) than E17-19 (483 genes), indicating the lack of functional circadian clocks in E10 mouse fetal hearts. In both mESCs and E10 embryos, CLOCK protein was absent despite the expression of Clock mRNA, which we showed was at least partially due to miRNA-mediated translational suppression of CLOCK. The CLOCK protein is required for the robust molecular oscillation in differentiated cells, and the post-transcriptional regulation of Clock plays a key role in setting the timing for the emergence of the circadian clock oscillation during mammalian development.

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Umemura Y, Koike N, Ohashi M, Tsuchiya Y, Meng QJ, Minami Y, Hara M, Hisatomi M, Yagita K