title: Influence of the estrous cycle on clock gene expression in reproductive tissues: effects of fluctuating ovarian steroid hormone levels.
abstract: Circadian rhythms in physiology and behavior are known to be influenced by the estrous cycle in female rodents. The clock genes responsible for the generation of circadian oscillations are widely expressed both within the central nervous system and peripheral tissues, including those that comprise the reproductive system. To address whether the estrous cycle affects rhythms of clock gene expression in peripheral tissues, we first examined rhythms of clock gene expression (Per1, Per2, Bmal1) in reproductive (uterus, ovary) and non-reproductive (liver) tissues of cycling rats using quantitative real-time PCR (in vivo) and luminescent recording methods to measure circadian rhythms of PER2 expression in tissue explant cultures from cycling PER2::LUCIFERASE (PER2::LUC) knockin mice (ex vivo). We found significant estrous variations of clock gene expression in all three tissues in vivo, and in the uterus ex vivo. We also found that exogenous application of estrogen and progesterone altered rhythms of PER2::LUC expression in the uterus. In addition, we measured the effects of ovarian steroids on clock gene expression in a human breast cancer cell line (MCF-7 cells) as a model for endocrine cells that contain both the steroid hormone receptors and clock genes. We found that progesterone, but not estrogen, acutely up-regulated Per1, Per2, and Bmal1 expression in MCF-7 cells. Together, our findings demonstrate that the timing of the circadian clock in reproductive tissues is influenced by the estrous cycle and suggest that fluctuating steroid hormone levels may be responsible, in part, through direct effects on the timing of clock gene expression.
authors.affiliation: Department of Psychiatry and Biobehavioral Sciences, University of California Los Angeles, Los Angeles, CA 90024, USA. tnakamura@mednet.ucla.edu
authors.forename: Takahiro J
authors.initials: TJ
authors.lastname: Nakamura
authors.forename: Michael T
authors.initials: MT
authors.lastname: Sellix
authors.forename: Takashi
authors.initials: T
authors.lastname: Kudo
authors.forename: Nobuhiro
authors.initials: N
authors.lastname: Nakao
authors.forename: Takashi
authors.initials: T
authors.lastname: Yoshimura
authors.forename: Shizufumi
authors.initials: S
authors.lastname: Ebihara
authors.forename: Christopher S
authors.initials: CS
authors.lastname: Colwell
authors.forename: Gene D
authors.initials: GD
authors.lastname: Block
mesh_terms: D056930:ARNTL Transcription Factors / Q000235:genetics / Q000378:metabolism; D000818:Animals; D001683:Biological Clocks / Q000235:genetics*; D045744:Cell Line, Tumor; D002940:Circadian Rhythm / Q000502:physiology*; D004967:Estrogens / Q000378:metabolism / Q000494:pharmacology*; D030762:Estrous Cycle / Q000502:physiology*; D005260:Female; D005786:Gene Expression Regulation / Q000187:drug effects*; D006801:Humans; D051379:Mice; D008822:Mice, Transgenic; D010053:Ovary / Q000378:metabolism*; D056950:Period Circadian Proteins / Q000235:genetics / Q000378:metabolism; D011374:Progesterone / Q000378:metabolism / Q000494:pharmacology*; D051381:Rats; D017208:Rats, Wistar
chemical_list: D056930:ARNTL Transcription Factors; D004967:Estrogens; C539022:PER1 protein, human; C421902:PER2 protein, human; C539023:Per1 protein, mouse; C513312:Per2 protein, mouse; D056950:Period Circadian Proteins; D011374:Progesterone