Polycomb Repressive Complex 2 in Eukaryotes-An Evolutionary Perspective.

María Guadalupe Trejo-Arellano,Mallika Vijayanathan,Iva Mozgová

doi:10.3390/epigenomes6010003

Abstract

Polycomb repressive complex 2 (PRC2) represents a group of evolutionarily conserved multi-subunit complexes that repress gene transcription by introducing trimethylation of lysine 27 on histone 3 (H3K27me3). PRC2 activity is of key importance for cell identity specification and developmental phase transitions in animals and plants. The composition, biochemistry, and developmental function of PRC2 in animal and flowering plant model species are relatively well described. Recent evidence demonstrates the presence of PRC2 complexes in various eukaryotic supergroups, suggesting conservation of the complex and its function. Here, we provide an overview of the current understanding of PRC2-mediated repression in different representatives of eukaryotic supergroups with a focus on the green lineage. By comparison of PRC2 in different eukaryotes, we highlight the possible common and diverged features suggesting evolutionary implications and outline emerging questions and directions for future research of polycomb repression and its evolution.

Highlights

DNA in the eukaryotic nucleus winds around octamers of histones, forming nucleosomes, the basic units of chromatin
As histone modifications introduced by polycomb repressive complexes (PRCs) are heritable during mitotic cell divisions, PRCs provide an epigenetic memory system required for stable cell identity, for an adequate response to external cues, and even for stable repression of genomic repeats
In line with its function in cell identity maintenance in animals, Polycomb repressive complex 2 (PRC2) dysfunction is frequently associated with cancer development and PRC2 is a potent target for anticancer therapy

Summary

Introduction

DNA in the eukaryotic nucleus winds around octamers of histones, forming nucleosomes, the basic units of chromatin. PRC1 was long considered to be animal specific since a homolog of Polycomb (Pc), the Drosophila PRC1-defining protein subunit [23], is missing in plants. PRC1 is present in plants, its core composition differs from animals and may have originated through convergent evolution (reviewed in the work of [28,29,30]). Homologs of Drosophila PRC2 subunits are conserved in mammals, fungi, plants, red algae, and diatoms (Figure 1, Table 1, Supplementary Table S1) ([60,61,62,63,64,65], reviewed in the work of [66,67,68,69]). The molecular structures have been determined for Drosophila, human, mouse, and the fungus Chaetomium thermophilum PRC2 (Figure 2) ([60,77,78,79,80], reviewed in the work of [34,81,82,83,84])

PRC2 in Ophithokonts

PRC2 Targeting to Repeats and Regions of Constitutive Heterochromatin

Findings

Emerging Patterns and Questions in PRC2 Evolution