Studies of alteration in histone methylation at whole-genome scale bring insight into gene regulation. Global changes in histone H3 are emerging as a new biomarker in malignant transformation [2, 3]. Likewise, histone-modifier enzymes control dynamic transcription of gene expression in normal and cancer cells, enabling key physiopathological processes to take place [4, 5]. Polycomb-group proteins (PcGs) are involved in silencing gene expression, particularly during development and differentiation stages [6, 7], and also play the major role in nuclear reprogramming and chromatin remodeling . PcGs are organized into two main polycomb-repressive complexes (PRCs), PRC1 and PRC2, that control gene silencing through post-translational histone modifications [9, 10].