Expression and Functional Analyses of Circadian Genes in Mouse Oocytes and Preimplantation Embryos: Cry1 Is Involved in the Meiotic Process Independently of Circadian Clock Regulation. Amano T et al. In mammals, circadian genes, Clock, Arntl (also known as Bmal1), Cry1, Cry2, Per1, Per2, and Per3, are rhythmically transcribed every 24 h in almost all organs and tissues to tick the circadian clock. However, their expression and function in oocytes and preimplantation embryos have not been investigated. In this study, we found that the circadian clock may stop in mouse oocytes and preimplantation embryos. Real-time PCR analysis revealed the presence of transcripts of these genes in both oocytes and preimplantation embryos; however, their amounts did not oscillate every 24 h in 1- to 4-cell and blastocyst-stage embryos. Moreover, immunofluorescence analyses revealed that CLOCK, ARNTL, and CRY1 were localized similarly in the nuclei of GV oocytes and 1- to 4-cell stage embryos. Since CRY1 is known to interact with the CLOCK-ARNTL complex to suppress transcription-promoting activity of the complex for genes such as Wee1, Cry2, Per1, Per2, and Per3 in cells having the ticking circadian clock, we hypothesized that if the circadian clock functions in GV oocytes and 1- to 4-cell stage embryos, CLOCK, ARNTL and CRY1 might suppress the transcription of these genes in GV oocytes and 1- to 4-cell stage embryos as well. As a result, knockdown of CRY1 in GV oocytes by RNA interference did not affect the transcription levels of Wee1, Cry2, Per1, Per2, and Per3 but reduced maturation ability. Thus, it seems that circadian genes are not involved in circadian clock regulation in mouse oocytes and preimplantation embryos but are involved in physiologies such as meiosis.
Expression regulated by
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Ovarian localization
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Circadian Clock Gene Expression in the Ovary: Effects of Luteinizing Hormone. Karman BN et al. A molecular device that measures time on a daily, or circadian, scale is a nearly ubiquitous feature of eukaryotic organisms. A core group of clock genes, whose coordinated function is required for this timekeeping, is expressed both in the central clock and within numerous peripheral organs. We examined expression of clock genes in the rat ovary. Transcripts for core oscillator elements (Arntl, Clock, Per1, Per2, Cry1) were present in the ovary as indicated by quantitative real-time RT-PCR. Rhythmic expression patterns of Arntl and Per2 transcripts and protein products were out-of-phase with respect to the central oscillator and in complete anti-phase to each other. Expression of Arntl was significantly elevated after the LH surge on the day of proestrus. Finally, human chorionic gonadotropin (hCG) treatment induced cyclic expression of both Arntl and Per2 gene products in hypophysectomized, immature rats primed with pregnant mares serum gonadotropin (eCG). Collectively, these data suggest that the core underpinnings of the transcriptional/translational feedback loop that drives circadian rhythmicity is present in the rat ovary. Furthermore, the study identifies luteinizing hormone (LH) as a potential regulator of circadian clock gene rhythms in the ovary.
Expression analysis of circadian genes in oocytes and preimplantation embryos of cattle and rabbits. Amano T et al. We previously showed that circadian genes clock, bmal1, cry1, cry2, per1, and per2 are expressed and function as maternal mRNA regulating events in the oocytes and preimplantation embryos of mice. Recent evidence indicates however that either or both expression profiles of circadian genes in some tissues, and transcript sequences of circadian genes, differ to generate the physiological differences between diurnal and nocturnal species. We therefore investigated the expression profiles of circadian genes in oocytes and preimplantation embryos of species other than mice, namely cattle and rabbits, representing diurnal and nocturnal species, respectively, and determined the protein sequences of circadian genes in these species. Quantitative real-time PCR revealed that all circadian genes considered in this study were present in the oocytes and preimplantation embryos of both species, and the transcript amounts of clock, cry1 and per1 contained in oocytes were significantly higher than in preimplantation embryos of both species. The transcripts of clock, cry1, and per1 of cattle and rabbits were determined by primer walking, and functional domains in the estimated amino acid sequences were compared between cattle and rabbits and with those of humans and mice. The sequences of clock, cry1, and per1 in cattle and rabbits closely resembled those in mice (85-100% homologies), and no difference based on diurnality or nocturnality was observed. These findings suggest that circadian genes in the oocytes and preimplantation embryos of mammals fulfill the same functions across species as maternal mRNA.