A search for such repressors using DNA methylation arrays suggested that the initiation of puberty was accompanied by changing promoter methylation of several members of the PcG repressive complex and genes encoding proteins that interact with the PcG system. If this change is predictive of opposite changes in gene expression, one would expect to find decreased hypothalamic expression of PcG genes either during puberty or immediately antedating the initiation of this event. Measuring the expression of most PcG components in the MBH by qPCR demonstrated an early decrease in Cbx7 and Eed mRNA abundance preceding the initiation of puberty, and a significant drop in Yy1 expression at mid-puberty. EED is a PRC2 component required for PcG action 32. The decrease in Cbx7 and Eed expression occurred independently from changes in ovarian estrogen output, as it was essentially complete before the pubertal increase in circulating estrogen levels.
