GSE123942
Epigenetic regulation of unique genes and repetitive elements by KRAB zinc finger protein ZFP57 in embryonic stem cells
KRAB-zinc finger proteins (KZFPs) represent one of the largest families of DNA binding proteins in vertebrate genomes and appear to have evolved to silence transposable elements (TEs) including endogenous retroviruses through sequence-specific targeting of repressive chromatin states. However, one member, ZFP57, is required to maintain the post-fertilization DNA methylation memory of parental-origin at genomic imprints. We have conducted RNA-seq and ChIP-seq analyses in normal and ZFP57 mutant ES cells to characterize the targets of ZFP57 in more detail. Over 80% of ZFP57 targets are TEs. However, mutants indicate that ZFP57 is not essential for their repression in ES cells. The remaining targets lie within unique imprinted and non-imprinted sequences. Though loss of ZFP57 influences imprinted genes as expected, the majority of unique gene targets lose H3K9me3 with little effect on DNA methylation and with very few exhibiting alterations in expression. Furthermore, comparison with DNA methyltransferase-deleted ES cells (TKO) identifies remarkably similar losses of H3K9me3 and changes in expression, defining regions where H3K9me3 is secondary to DNA methylation. We determine that ZFP57 is the principal methylation-sensitive KZFP recruiting KAP1 and H3K9me3 in ES cells. Finally, like imprints, other unique targets of ZFP57 are enriched for germline-derived DNA methylation including oocyte-specific methylation that is resistant to post-fertilisation epigenetic reprogramming. Our analyses suggest the evolution of a DNA methylation sensitive KZFP, that may serve to reinforce the silenced state at TEs, but whose primary function is to maintain DNA methylation and repressive histone marks at imprinted regions. Overall design: ChIP-seq using WT and ZFP57 KO ESCs for ZFP57, KAP1 and H3K9me3. RNA-seq using the same WT and KO ESCs. Additional ChIP-seq for H3K9me3 using hybrid ES cells with maternal zygotic ZFP57 deletion. Sequencing was performed using Illumina HiSeq 2000 and HiSeq 4000 platforms. All data were mapped to mm10.