To determine if the changes in promoter DNA methylation of PcG genes suggested by the arrays are accompanied by altered gene expression, we focused our attention on the PcG complex and measured by quantitative (q) PCR the mRNA abundance of most members of this complex in the MBH at the time of puberty. We observed that only expression of two PcG genes required for appropriate PcG function 29, 32, the PRC1 member Cbx7 and the PRC2 member Eed (not represented in the DNA arrays), decreases at LJ, i.e., at the time when puberty is initiated in the female rat 2. This reduction was maintained throughout puberty (Fig. 3a), seemingly unaffected by the peripubertal increase in serum estradiol levels (Fig. 3b), but was prevented by the administration of Aza (Fig. 3a). Among the other members of the PcG complex examined, only Yy1 mRNA levels decreased significantly at puberty, but this decrease occurred much more gradually (Supplementary Fig. 3). No reduction in mRNA levels of any member of the PcG complex, including Cbx7 and Eed, was seen in the preoptic area (POA) region during puberty (Supplementary Fig. 3), indicating that the pubertal decrease in Cbx7 and Eed expression is MBH-specific.
