title: Epigenetic modifiers are necessary but not sufficient for reprogramming non-myelinating cells into myelin gene-expressing cells.
abstract: BACKGROUND
  Modifications on specific histone residues and DNA methylation play an essential role in lineage choice and cellular reprogramming. We have previously shown that histone modifications or combinatorial codes of transcription factors (TFs) are critical for the differentiation of multipotential progenitors into myelinating oligodendrocytes. In this study we asked whether combining global manipulation of DNA methylation and histone acetylation together with the expression of oligodendrocyte-specific TFs, was sufficient to switch the identity of fibroblasts into myelin gene-expressing cells.
  
  
  RESULTS
  Transfection of six oligodendrocyte-specific TFs (Olig1, Olig2, Sox10, Mash1, E47 and Nkx2.2) into NIH3T3 fibroblasts was capable of inducing expression of myelin gene promoter-driven reporters, but did not activate endogenous myelin gene expression. These results suggested the existence of a transcriptionally incompetent chromatin conformation in NIH3T3 fibroblasts. Using chromatin immunoprecipitation (ChIP) analysis, we compared the histone code on the conserved regions of myelin genes (i.e. Mbp and Mag) in differentiating oligodendrocyte progenitors and NIH3T3 fibroblasts. Chromatin at myelin gene loci was characterized by the presence of repressive histone modifications (me3K9H3 and me3K27H3) in NIH3T3 fibroblasts and active histone marks (me3K4H3 and AcH3) in oligodendrocyte lineage cells. To induce a transcriptionally competent chromatin signature, NIH3T3 fibroblasts were treated with 5-azadeoxy-citidine (5-AzaC) to decrease DNA methylation, and trichostatin A (TSA) or sirtinol, to favor histone acetylation. Treatment with 5-AzaC/TSA but not sirtinol, resulted in the detection of endogenous myelin gene transcripts in fibroblasts, although not to the levels detected in myelinating cells. Transfection of oligodendrocyte-specific TFs after 5-AzaC/TSA treatment did not further increase myelin gene expression, nor did it reprogram the transcriptional network of NIH3T3 fibroblasts into that of oligodendrocytes.
  
  
  CONCLUSIONS
  These results suggest that reprogramming of fibroblasts into myelin gene-expressing cells not only requires transcriptional activation, but also chromatin manipulations that go beyond histone acetylation and DNA methylation.
authors.affiliation: Department of Neuroscience, Mount Sinai School of Medicine, New York, New York, United States of America.
authors.forename: Jia
authors.initials: J
authors.lastname: Liu
authors.forename: Juan
authors.initials: J
authors.lastname: Sandoval
authors.forename: Sung Tae
authors.initials: ST
authors.lastname: Doh
authors.forename: Li
authors.initials: L
authors.lastname: Cai
authors.forename: Gerardo
authors.initials: G
authors.lastname: López-Rodas
authors.forename: Patrizia
authors.initials: P
authors.lastname: Casaccia
mesh_terms: D000107:Acetylation; D000818:Animals; D002454:Cell Differentiation; D002460:Cell Line; D019070:Cell Lineage; D002478:Cells, Cultured; D002843:Chromatin / Q000235:genetics / Q000378:metabolism; D019175:DNA Methylation; D044127:Epigenesis, Genetic; D005347:Fibroblasts / Q000166:cytology* / Q000378:metabolism; D015870:Gene Expression; D006657:Histones / Q000235:genetics / Q000378:metabolism; D000090322:Homeobox Protein Nkx-2.2; D051379:Mice; D039902:Multipotent Stem Cells / Q000166:cytology / Q000378:metabolism; D009185:Myelin Proteins / Q000235:genetics* / Q000378:metabolism; D041681:NIH 3T3 Cells; D009836:Oligodendroglia / Q000166:cytology* / Q000378:metabolism; D051381:Rats; D014157:Transcription Factors / Q000235:genetics / Q000378:metabolism
chemical_list: D002843:Chromatin; D006657:Histones; D000090322:Homeobox Protein Nkx-2.2; D009185:Myelin Proteins; C000715627:Nkx2-2 protein, mouse; C000715628:Nkx2-2 protein, rat; D014157:Transcription Factors