title: Undifferentiated hematopoietic cells are characterized by a genome-wide undermethylation dip around the transcription start site and a hierarchical epigenetic plasticity.
abstract: Evidence for the epigenetic regulation of hematopoietic stem cells (HSCs) is growing, but the genome-wide epigenetic signature of HSCs and its functional significance remain unclear. In this study, from a genome-wide comparison of CpG methylation in human CD34(+) and CD34(-) cells, we identified a characteristic undermethylation dip around the transcription start site of promoters and an overmethylation of flanking regions in undifferentiated CD34(+) cells. This "bivalent-like" CpG methylation pattern around the transcription start site was more prominent in genes not associated with CpG islands (CGI(-)) than CGI(+) genes. Undifferentiated hematopoietic cells also exhibited dynamic chromatin associated with active transcription and a higher turnover of histone acetylation than terminally differentiated cells. Interestingly, inhibition of chromatin condensation by chemical treatment (5-azacytidine, trichostatin A) enhanced the self-renewal of "stimulated" HSCs in reconstituting bone marrows but not "steady-state" HSCs in stationary phase bone marrows. In contrast, similar treatments on more mature cells caused partial phenotypic dedifferentiation and apoptosis at levels correlated with their hematopoietic differentiation. Taken together, our study reveals that the undifferentiated state of hematopoietic cells is characterized by a unique epigenetic signature, which includes dynamic chromatin structures and an epigenetic plasticity that correlates to level of undifferentiation.
authors.affiliation: Catholic Institute of Cell Therapy & Department of Cellular Medicine, College of Medicine, Catholic University of Korea, Seoul.
authors.forename: Yun Shin
authors.initials: YS
authors.lastname: Chung
authors.forename: Hye Joung
authors.initials: HJ
authors.lastname: Kim
authors.forename: Tae-Min
authors.initials: TM
authors.lastname: Kim
authors.forename: Sung-Hyun
authors.initials: SH
authors.lastname: Hong
authors.forename: Kyung-Rim
authors.initials: KR
authors.lastname: Kwon
authors.forename: Sungwhan
authors.initials: S
authors.lastname: An
authors.forename: Jung-Hoon
authors.initials: JH
authors.lastname: Park
authors.forename: Suman
authors.initials: S
authors.lastname: Lee
authors.forename: Il-Hoan
authors.initials: IH
authors.lastname: Oh
mesh_terms: D000107:Acetylation; D000818:Animals; D018952:Antigens, CD34 / Q000096:biosynthesis; D015153:Blotting, Western; D002454:Cell Differentiation / Q000235:genetics*; D018899:CpG Islands; D019175:DNA Methylation / Q000235:genetics*; D044127:Epigenesis, Genetic / Q000235:genetics; D006412:Hematopoietic Stem Cells / Q000166:cytology* / Q000378:metabolism; D006801:Humans; D051379:Mice; D008810:Mice, Inbred C57BL; D011401:Promoter Regions, Genetic; D024363:Transcription Initiation Site
chemical_list: D018952:Antigens, CD34