To search for potential repressor genes that may become more methylated in the hypothalamus at puberty, we used DNA methylation arrays to interrogate the MBH at different pubertal stages (EJ, LJ and LP) (data available at http://www.ncbi.nlm.nih.gov/gds/?term=GSE38505). EJ and LJ were defined earlier; the LP (late proestrus) phase of puberty corresponds to the day of the first preovulatory surge of gonadotropins, which in the rat can be considered as mid-puberty 2. Using the bioinformatics methods described in the on-line Supplementary Information section, we observed that genes with a pattern of changing methylation at either the LJ or LP phases of puberty were functionally enriched for a cluster of chromatin/histone modification terms. Several of these genes are components of a common regulatory domain as they were either members of the PcG silencing complex (Cbx7, Cbx8, Phc3, Ring1B/Rnf2, and Yy1) or encoded proteins that interact with PcG proteins (Rybp, Csnk2b, Kdm2b). With the exception of Ring1B/Rnf2, all of these genes exhibited a general pattern of increased promoter methylation at puberty (Supplementary Fig. 2), suggesting that the PcG silencing complex may undergo functionally important epigenetic changes with the advent of puberty.
