A NuRD Complex from Xenopus laevis Eggs Is Essential for DNA Replication during Early Embryogenesis

Christo P Christov,Kevin S Dingwell,Mark Skehel,Helen S Wilkes,Julian E Sale,James C Smith,Torsten Krude

doi:10.1016/j.celrep.2018.02.015

Christo P Christov, Kevin S Dingwell + Show 5 more

Open Access

https://doi.org/10.1016/j.celrep.2018.02.015

Copy DOI

Abstract

SummaryDNA replication in the embryo of Xenopus laevis changes dramatically at the mid-blastula transition (MBT), with Y RNA-independent random initiation switching to Y RNA-dependent initiation at specific origins. Here, we identify xNuRD, an MTA2-containing assemblage of the nucleosome remodeling and histone deacetylation complex NuRD, as an essential factor in pre-MBT Xenopus embryos that overcomes a functional requirement for Y RNAs during DNA replication. Human NuRD complexes have a different subunit composition than xNuRD and do not support Y RNA-independent initiation of DNA replication. Blocking or immunodepletion of xNuRD inhibits DNA replication initiation in isolated nuclei in vitro and causes inhibition of DNA synthesis, developmental delay, and embryonic lethality in early embryos. xNuRD activity declines after the MBT, coinciding with dissociation of the complex and emergence of Y RNA-dependent initiation. Our data thus reveal an essential role for a NuRD complex as a DNA replication factor during early Xenopus development.

Highlights

Accurate replication of chromosomal DNA is essential for cell proliferation, development, and homeostasis of multicellular organisms
A Y RNA-Independent Initiation Activity from Xenopus Egg Extracts The initiation step of chromosomal DNA replication can be reconstituted in a human cell-free system in which late G1 phase template nuclei are incubated in a cytosolic extract from proliferating cells (Krude, 2000)
Of the 17 proteins that were enriched in both experimental replicates, we identified four subunits of the nucleosome remodeling and deacetylation complex NuRD: MTA2, GATAD2/p66, CHD4, and RBBP4/p48 (Figure 2C)

Summary

Introduction

Accurate replication of chromosomal DNA is essential for cell proliferation, development, and homeostasis of multicellular organisms. The principles of chromosomal DNA replication are evolutionarily conserved in eukaryotes, but regulation of the initiation of DNA replication changes considerably during early vertebrate development. In Xenopus laevis, the mid-blastula transition (MBT) marks a turning point for several features of DNA replication (Hyrien et al, 1995; Lemaitre et al, 1998; Montag et al, 1988; Newport and Kirschner, 1982a, 1982b). In activated eggs and pre-MBT embryos, cell divisions alternate and even partly overlap with very short S phases, during which tens of thousands of replication forks are established without site specificity and in the absence of transcription. After the MBT, bulk transcription of zygotic genes occurs, and DNA replication initiates at defined replication origins, which often overlap with transcription start sites. S phase and mitosis become separated by G1 and G2 phases, and the duration of S phase extends to several hours

Results

Discussion

Conclusion