Functional analysis of AEBP2, a PRC2 Polycomb protein, reveals a Trithorax phenotype in embryonic development and in ESCs.

Anne Grijzenhout,Dorota Szumska,Benedikt M Kessler,Shoumo Bhattacharya,Haruhiko Koseki,Michal Ryszard Gdula,Joanna F Mcgouran,Jonathan Godwin,Neil Brockdorff,Sarah Cooper

doi:10.1242/dev.123935

Abstract

The Polycomb repressive complexes PRC1 and PRC2 are key mediators of heritable gene silencing in multicellular organisms. Here, we characterise AEBP2, a known PRC2 co-factor which, in vitro, has been shown to stimulate PRC2 activity. We show that AEBP2 localises specifically to PRC2 target loci, including the inactive X chromosome. Proteomic analysis confirms that AEBP2 associates exclusively with PRC2 complexes. However, analysis of embryos homozygous for a targeted mutation of Aebp2 unexpectedly revealed a Trithorax phenotype, normally linked to antagonism of Polycomb function. Consistent with this, we observe elevated levels of PRC2-mediated histone H3K27 methylation at target loci in Aebp2 mutant embryonic stem cells (ESCs). We further demonstrate that mutant ESCs assemble atypical hybrid PRC2 subcomplexes, potentially accounting for enhancement of Polycomb activity, and suggesting that AEBP2 normally plays a role in defining the mutually exclusive composition of PRC2 subcomplexes.

Highlights

Polycomb group proteins, which were initially identified for their role in heritable silencing of Hox gene clusters in Drosophila melanogaster, are highly conserved in vertebrates (Simon and Kingston, 2009)
We suggest that perturbance of this function in Aebp2 mutant embryonic stem cells (ESCs) may lead to aberrant PRC2 activity, which could account for the observed increase of H3K27me3 at PRC2 targets and the Trithorax phenotype
Removal of AEBP2 in mice leads to a Trithorax phenotype To investigate the role of AEBP2 within the PRC2 complex, we established a knockout mouse model that truncates Aebp2 transcripts for both the long and short isoforms before exon 2 (Aebp2tr), resulting in a protein that does not contain the conserved zinc-finger and KR domains (Fig. 1A; Fig. S1A)

Summary

Introduction

Polycomb group proteins, which were initially identified for their role in heritable silencing of Hox gene clusters in Drosophila melanogaster, are highly conserved in vertebrates (Simon and Kingston, 2009). Polycomb proteins confer epigenetic repression by modification of chromatin. The Trithorax group proteins act to antagonise Polycomb function and have a role in developmental gene activation (Steffen and Ringrose, 2014).

Methods

Results

Conclusion