Figure 5.

Chronology of epigenetic regulation during the circadian rhythm and menstrual cycle. The regulation of biological cycles like the Circadian rhythm and Menstrual cycle in females has been shown to work through epigenetic regulatory mechanisms. (The figure is relative and not accurate to scale). (A) The gene Bmal1 is the master regulator of the circadian rhythm. The graph represents the relative density of the two active histone marks H3K3me and H3K4me on Bmal1 through a 26-hour period. ZT is Zeitgeber Time where ZT0 corresponds to light on and ZT12 to light off. The peaks represent the maxima of the two-histone marks with respect to ZT, similarly, the dips represent the minima. This shows differential expression of the gene with respect to time, which has an epigenetic regulatory basis. (B) The graph represents the global acetylation profile from endometrial tissue through the 28-day menstrual cycle. The peaks represent the maxima and the dips represent the minima of the histone marks with respect to time. Global changes in the histone acetylation profile show that these marks contribute to the induction of different genes during different stages of the cycle. Hence they are responsible for the variable morphology of the endometrium through the 28-day period. These epigenetic changes are thus the basis for changes in the endometrial morphology like regeneration (1–7 days), proliferation (7–14 days), ovulation (13–17 days), differentiation (15–22 days), degradation (22–28 days) during the proliferative phase and secretory phase.