Ring1-mediated ubiquitination of H2A restrains poised RNA polymerase II at bivalent genes in mouse ES cells.
Changes in phosphorylation of the carboxy-terminal domain (CTD) of RNA polymerase II (RNAP) are associated with transcription initiation, elongation and termination. Sites of active transcription are generally characterized by hyperphosphorylated RNAP, particularly at Ser 2 residues, whereas inactive or poised genes may lack RNAP or may bind Ser 5-phosphorylated RNAP at promoter proximal regions. Recent studies have demonstrated that silent developmental regulator genes have an unusual histone modification profile in ES cells, being simultaneously marked with Polycomb repressor-mediated histone H3K27 methylation, and marks normally associated with gene activity. Contrary to the prevailing view, we show here that this important subset of developmental regulator genes, termed bivalent genes, assemble RNAP complexes phosphorylated on Ser 5 and are transcribed at low levels. We provide evidence that this poised RNAP configuration is enforced by Polycomb Repressor Complex (PRC)-mediated ubiquitination of H2A, as conditional deletion of Ring1A and Ring1B leads to the sequential loss of ubiquitination of H2A, release of poised RNAP, and subsequent gene de-repression. These observations provide an insight into the molecular mechanisms that allow ES cells to self-renew and yet retain the ability to generate multiple lineage outcomes.
Nuclear Organisation, MRC Clinical Sciences Centre, Imperial College School of Medicine, Hammersmith Hospital Campus, Du Cane Road, London W12 0NN, UK.
Julie K
JK
Stock
Sara
S
Giadrossi
Miguel
M
Casanova
Emily
E
Brookes
Miguel
M
Vidal
Haruhiko
H
Koseki
Neil
N
Brockdorff
Amanda G
AG
Fisher
Ana
A
Pombo
D000818:Animals; D002478:Cells, Cultured; D004268:DNA-Binding Proteins / Q000502:physiology*; D053595:Embryonic Stem Cells; D018507:Gene Expression Regulation, Developmental; D006657:Histones / Q000378:metabolism*; D056484:Jumonji Domain-Containing Histone Demethylases; D051379:Mice; D018345:Mice, Knockout; D010089:Oxidoreductases, N-Demethylating / Q000378:metabolism; D010766:Phosphorylation; D063150:Polycomb Repressive Complex 1; D063146:Polycomb-Group Proteins; D012319:RNA Polymerase II / Q000502:physiology*; D012097:Repressor Proteins / Q000502:physiology; D014158:Transcription, Genetic; D044767:Ubiquitin-Protein Ligases; D054875:Ubiquitination
D004268:DNA-Binding Proteins; D006657:Histones; D063146:Polycomb-Group Proteins; D012097:Repressor Proteins; D056484:Jumonji Domain-Containing Histone Demethylases; C523761:Kdm6b protein, mouse; D010089:Oxidoreductases, N-Demethylating; D063150:Polycomb Repressive Complex 1; C489840:Ring1 protein, mouse; C489842:Rnf2 protein, mouse; D044767:Ubiquitin-Protein Ligases; D012319:RNA Polymerase II