MGA, L3MBTL2 and E2F6 determine genomic binding of the non-canonical Polycomb repressive complex PRC1.6

PLoS Genet. 2018 Jan 30;14(1):e1007193. doi: 10.1371/journal.pgen.1007193. eCollection 2018 Jan.

Abstract

Diverse Polycomb repressive complexes 1 (PRC1) play essential roles in gene regulation, differentiation and development. Six major groups of PRC1 complexes that differ in their subunit composition have been identified in mammals. How the different PRC1 complexes are recruited to specific genomic sites is poorly understood. The Polycomb Ring finger protein PCGF6, the transcription factors MGA and E2F6, and the histone-binding protein L3MBTL2 are specific components of the non-canonical PRC1.6 complex. In this study, we have investigated their role in genomic targeting of PRC1.6. ChIP-seq analysis revealed colocalization of MGA, L3MBTL2, E2F6 and PCGF6 genome-wide. Ablation of MGA in a human cell line by CRISPR/Cas resulted in complete loss of PRC1.6 binding. Rescue experiments revealed that MGA recruits PRC1.6 to specific loci both by DNA binding-dependent and by DNA binding-independent mechanisms. Depletion of L3MBTL2 and E2F6 but not of PCGF6 resulted in differential, locus-specific loss of PRC1.6 binding illustrating that different subunits mediate PRC1.6 loading to distinct sets of promoters. Mga, L3mbtl2 and Pcgf6 colocalize also in mouse embryonic stem cells, where PRC1.6 has been linked to repression of germ cell-related genes. Our findings unveil strikingly different genomic recruitment mechanisms of the non-canonical PRC1.6 complex, which specify its cell type- and context-specific regulatory functions.

Publication types

  • Research Support, Non-U.S. Gov't

MeSH terms

  • Animals
  • Basic Helix-Loop-Helix Transcription Factors / genetics
  • Basic Helix-Loop-Helix Transcription Factors / physiology*
  • Cells, Cultured
  • DNA / metabolism*
  • E2F6 Transcription Factor / genetics
  • E2F6 Transcription Factor / physiology*
  • Gene Expression Regulation
  • Gene Knockdown Techniques
  • HEK293 Cells
  • Human Embryonic Stem Cells / physiology
  • Humans
  • Mice
  • Mouse Embryonic Stem Cells / physiology
  • Nuclear Proteins / genetics
  • Nuclear Proteins / physiology*
  • Polycomb Repressive Complex 1 / metabolism*
  • Protein Binding / genetics
  • Transcription Factors / genetics
  • Transcription Factors / physiology*

Substances

  • Basic Helix-Loop-Helix Transcription Factors
  • E2F6 Transcription Factor
  • E2F6 protein, human
  • L3MBTL2 protein, human
  • MGA protein, human
  • Nuclear Proteins
  • Transcription Factors
  • DNA
  • Polycomb Repressive Complex 1

Grants and funding

This work was supported by a grant of the Deutsche Forschungsgemeinschaft (DFG) to GS (TRR81-A06). The funders had no role in study design, data collection and analysis, decision to publish, or preparation of the manuscript.