Chromatin proteins and RNA are associated with DNA during all phases of mitosis.

Kathryn L Black,Jeffrey L Caplan,Tyler K Fenstermaker,Svetlana Petruk,Jacob W Hodgson,Alexander Mazo,Hugh W Brock

doi:10.1038/celldisc.2016.38

Abstract

Mitosis brings about major changes to chromosome and nuclear structure. We used recently developed proximity ligation assay-based techniques to investigate the association with DNA of chromatin-associated proteins and RNAs in Drosophila embryos during mitosis. All groups of tested proteins, histone-modifying and chromatin-remodeling proteins and methylated histones remained in close proximity to DNA during all phases of mitosis. We also found that RNA transcripts are associated with DNA during all stages of mitosis. Reduction of H3K27me3 levels or elimination of RNAs had no effect on the association of the components of PcG and TrxG complexes to DNA. Using a combination of proximity ligation assay-based techniques and super-resolution microscopy, we found that the number of protein–DNA and RNA–DNA foci undergoes significant reduction during mitosis, suggesting that mitosis may be accompanied by structural re-arrangement or compaction of specific chromatin domains.

Highlights

DNA replication [1, 2] and mitosis [3,4,5] are the two phases of the cell cycle during which epigenetic marks must be inherited
We show that RNAs and multiple chromatin proteins, including PcG and TrxG histonemodifying enzymes, chromatin-remodeling factors and major forms of methylated histones remain associated with a limited number of foci on DNA during all phases of mitosis
Using Chromatin Association Assay (CAA), we asked whether modified histones are associated with DNA during mitosis

Summary

Introduction

DNA replication [1, 2] and mitosis [3,4,5] are the two phases of the cell cycle during which epigenetic marks must be inherited. Mitosis is accompanied by genome-wide cessation of transcription [7] at early mitotic stages [8] and is associated with global phosphorylation of transcription factors and histone H3 (H3Thr and H3Ser10) [9, 10], as well as deacetylation of histones [11]. Epigenetic bookmarking during mitosis is thought to include modified histones, histone modifiers, nucleosome remodeling and transcriptional machineries, transcription factors and non-coding (nc) RNAs [12,13,14,15]. Some of these proteins dissociate during all or some stages of mitosis, while others remain on mitotic chromosomes. We showed that in human lymphoblast cells RNAs are stable through all stages of mitosis [16]

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Conclusion