Circadian rhythms in the mouse reproductive axis during the estrous cycle and pregnancy

Mar 5, 2020Journal of neuroscience research

Daily biological rhythms in the mouse reproductive system during the reproductive cycle and pregnancy

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Abstract

Changes in peak times of reproductive tissue rhythms occurred during the estrous cycle and late pregnancy.

The phase relationships of circadian rhythms in the SCN, pituitary, uterus, and ovary were altered throughout the estrous cycle and late pregnancy.
PER2::LUC period changes were observed in the SCN, uterus, and ovary during these reproductive stages.
Progesterone was found to increase Per2-luciferase expression in specific brain cells and to shorten the PER2::LUC period in uterine tissue during pregnancy.
Activity levels in PER2::LUC mice decreased during pregnancy, with a delayed onset of activity.
The altered locomotor activity onset did not correspond with changes in PER2::LUC period in the SCN or arcuate nucleus.

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Molecular and behavioral timekeeping is regulated by the circadian system which includes the brain's suprachiasmatic nucleus (SCN) that translates environmental light information into neuronal and endocrine signals aligning peripheral tissue rhythms to the time of day. Despite the critical role of circadian rhythms in fertility, it remains unexplored how circadian rhythms change within reproductive tissues during pregnancy. To determine how estrous cycle and pregnancy impact phase relationships of reproductive tissues, we used PER2::Luciferase (PER2::LUC) circadian reporter mice and determined the time of day of PER2::LUC peak (phase) in the SCN, pituitary, uterus, and ovary. The relationships between reproductive tissue PER2::LUC phases changed throughout the estrous cycle and late pregnancy and were accompanied by changes to PER2::LUC period in the SCN, uterus, and ovary. To determine if the phase relationship adaptations were driven by sex steroids, we asked if progesterone, a hormone involved in estrous cyclicity and pregnancy, could regulate Per2-luciferase expression. Using an in vitro transfection assay, we found that progesterone increased Per2-luciferase expression in immortalized SCN (SCN2.2) and arcuate nucleus (KTAR) cells. In addition, progesterone shortened PER2::LUC period in ex vivo uterine tissue recordings collected during pregnancy. As progesterone dramatically increases during pregnancy, we evaluated wheel-running patterns in PER2::LUC mice. We confirmed that activity levels decrease during pregnancy and found that activity onset was delayed. Although SCN, but not arcuate nucleus, PER2::LUC period changed during late pregnancy, onset of locomotor activity did not correlate with SCN or arcuate nucleus PER2::LUC period.

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Circadian rhythms in the mouse reproductive axis during the estrous cycle and pregnancy

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