Circadian gene activity in mouse egg cells and early embryos shows Cry1 helps cell division independently of the body’s internal clock

Circadian genes do not show rhythmic transcription in mouse oocytes and preimplantation embryos.

• Transcripts of circadian genes Clock, Arntl, Cry1, Cry2, Per1, Per2, and Per3 were detected in mouse oocytes and preimplantation embryos.
• The amounts of these transcripts did not oscillate every 24 hours in one- to four-cell and blastocyst-stage embryos.
• CLOCK, ARNTL, and CRY1 proteins were similarly localized in the nuclei of germinal vesicle oocytes and one- to four-cell-stage embryos.
• Knockdown of CRY1 in germinal vesicle oocytes did not alter the transcription levels of circadian genes but reduced maturation ability.
• Circadian genes may not regulate the circadian clock in mouse oocytes and preimplantation embryos, but they could play a role in physiological processes like meiosis.

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