The evolving epigenome

Epigenetic studies include the investigation of DNA methylation, histone modifications, chromatin remodeling and gene regulation by noncoding RNAs (ncRNAs). Epigenetic alterations are critical for early developmental processes, the silencing of the inactive X-chromosome and tissue-specific gene regulation. A comprehensive picture of epigenetic patterns in normal cells is now emerging; these patterns are disturbed in human diseases such as cancer. In this review, we highlight some of the most recent advances and discoveries in the field. First, while DNA methylation is known for many years, we are just beginning to learn about novel modifications of the DNA such as 5-hydroxymethylation and the enzymes that establish and remove these marks (e.g. TET1, TET2, TET3). Furthermore, altered epigenetic patterns in diseases might be linked to recurrent mutations within enzymes required for the establishment, maintenance and editing of these patterns. Examples are mutations in the gene encoding chromatin remodeling factor SMARCB1 in rhabdoid tumors or mutations in one of the three histone H3.3-encoding genes, H3F3A, in pediatric glioblastomas. A further focus in this review will be on recent findings in the field of ncRNAs as exemplified by the long noncoding RNA CTBP1-AS involved in prostate cancer and circular RNA CDR1as which captures and negatively regulates microRNA mir-7. Finally, we will highlight some of the novel technologies that have recently emerged in the field and will help in the profiling of disease genomes by allowing the use of small cell numbers and a higher resolution.