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Abstract
Precise timing in hormone release from the hypothalamus, the pituitary and ovary is
critical for fertility. Hormonal release patterns of the reproductive axis are regulated
by a feedback loop within the hypothalamic-pituitary-gonadal (HPG) axis. The timing
and rhythmicity of hormone release and tissue sensitivity in the HPG axis is regulated
by circadian clocks located in the hypothalamus (suprachiasmatic nucleus, kisspeptin
and GnRH neurons), the pituitary (gonadotrophs), the ovary (theca and granulosa cells),
the testis (Leydig cells), as well as the uterus (endometrium and myometrium). The
circadian clocks integrate environmental and physiological signals to produce cell
endogenous rhythms generated by a transcriptional-translational feedback loop of transcription
factors that are collectively called the “molecular clock”. This review specifically
focuses on the contribution of molecular clock transcription factors in regulating
hormone release patterns in the reproductive axis, with an emphasis on the female
reproductive system. Specifically, we discuss the contributions of circadian rhythms
in distinct neuronal populations of the female hypothalamus, the molecular clock in
the pituitary and its overall impact on female and male fertility.