Expression and Functional Analyses of Circadian Genes in Mouse Oocytes and Preimplantation Embryos: Cry1 Is Involved in the Meiotic Process Independently of Circadian Clock Regulation1

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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