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

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.

The stoichiometry and interactome of the Nucleosome Remodeling and Deacetylase (NuRD) complex are conserved across multiple cell lines

“…It has been suggested that gene regulatory complexes such as the COMPASS , PRC2 and the BAP1 complexes can play cytoplasmic roles. Indeed, enzymatically active subcomplexes of NuRD have also been observed in the cytosol . However, SLC25A5 has also been convincingly shown to be present in the nucleus .…”

Genome wide decrease of DNA replication eye density at the midblastula transition ofXenopus laevis

“…In support of this model it has been shown, though at only one stage post-MBT, that overexpression of four replication initiation factors (Treslin, RecQ4, Drf1, TopBP1) delays the onset of the MBT in Xenopus laevis and reduces replication track distances [21]. Other factors such as protein phosphatase 2A [22], non-coding Y RNAs [23], the chromatin remodeling complex xNuRD [24], histones [25], Rap1 interacting factor (Rif1) [26] and dNTP pools have also been linked to the change of DNA replication program or the DNA:cytoplasm ratio at the MBT. Injection of dNTPs into early embryos leads to extra cleavage cycles [27], and early embryos treated with the ribonucleotide reductase (RNR) inhibitor hydroxyurea (HU) are arrested at the MBT [28].…”

Preserving Genome Integrity during the Early Embryonic DNA Replication Cycles

“…Recently, a requirement for early cleavages DNA replication of a large chromatin remodeling complex xNuRD, has been highlighted in early Xenopus embryos. Before MBT, this complex seems to ensure the function of small non coding Y-RNAs in replication initiation observed after MBT [21,22], however the molecular mechanism involved remains currently unclear [23]. Furthermore, while Y-RNAs function appears to be conserved in somatic human cells, NuRD activity is not shared.…”