title: Active DNA demethylation in human postmitotic cells correlates with activating histone modifications, but not transcription levels.
abstract: BACKGROUND
  In mammals, the dynamics of DNA methylation, in particular the regulated, active removal of cytosine methylation, has remained a mystery, partly due to the lack of appropriate model systems to study DNA demethylation. Previous work has largely focused on proliferating cell types that are mitotically arrested using pharmacological inhibitors to distinguish between active and passive mechanisms of DNA demethylation.
  
  
  RESULTS
  We explored this epigenetic phenomenon in a natural setting of post-mitotic cells: the differentiation of human peripheral blood monocytes into macrophages or dendritic cells, which proceeds without cell division. Using a global, comparative CpG methylation profiling approach, we identified many novel examples of active DNA demethylation and characterized accompanying transcriptional and epigenetic events at these sites during monocytic differentiation. We show that active DNA demethylation is not restricted to proximal promoters and that the time-course of demethylation varies for individual CpGs. Irrespective of their location, the removal of methylated cytosines always coincided with the appearance of activating histone marks.
  
  
  CONCLUSIONS
  Demethylation events are highly reproducible in monocyte-derived dendritic cells from different individuals. Our data suggest that active DNA demethylation is a precisely targeted event that parallels or follows the modification of histones, but is not necessarily coupled to alterations in transcriptional activity.
authors.affiliation: Department of Hematology, University Hospital Regensburg, Franz-Josef-Strauss-Allee 11, 93042 Regensburg, Germany.
authors.forename: Maja
authors.initials: M
authors.lastname: Klug
authors.forename: Sven
authors.initials: S
authors.lastname: Heinz
authors.forename: Claudia
authors.initials: C
authors.lastname: Gebhard
authors.forename: Lucia
authors.initials: L
authors.lastname: Schwarzfischer
authors.forename: Stefan W
authors.initials: SW
authors.lastname: Krause
authors.forename: Reinhard
authors.initials: R
authors.lastname: Andreesen
authors.forename: Michael
authors.initials: M
authors.lastname: Rehli
mesh_terms: D002454:Cell Differentiation; D049109:Cell Proliferation; D019175:DNA Methylation / Q000235:genetics*; D003713:Dendritic Cells / Q000166:cytology / Q000378:metabolism; D020869:Gene Expression Profiling; D005786:Gene Expression Regulation; D006657:Histones / Q000235:genetics / Q000378:metabolism*; D006801:Humans; D008264:Macrophages / Q000166:cytology / Q000378:metabolism; D008938:Mitosis / Q000235:genetics*; D008957:Models, Genetic; D009000:Monocytes / Q000166:cytology* / Q000378:metabolism*; D020411:Oligonucleotide Array Sequence Analysis; D011401:Promoter Regions, Genetic / Q000235:genetics; D011499:Protein Processing, Post-Translational / Q000235:genetics*; D012333:RNA, Messenger / Q000235:genetics / Q000378:metabolism; D014158:Transcription, Genetic
chemical_list: D006657:Histones; D012333:RNA, Messenger