Genomic association of the imprinting maintenance factor ZFP57 and associated chromatin regulators in murine embryonal stem cells at imprinted and non imprinted loci and its expression in the developing mouse embryo

Several lines of evidence have provided clues for the pivotal role played by the KRAB-containing zinc finger protein ZFP57 in the maintenance of the parent of origin-dependent epigenetic state, DNA methylation and histone tails specific modifications, of the hundreds imprinted loci in mouse which include several non coding RNAs. ZFP57 associates with KAP1, a general co-repressor of the abundant KRAB-ZFPs family, which acts as a scaffold for the recruitment of chromatin modifiers that include the histone H3 methyltransferase SETDB1 and heterochromatin protein-1 (HP1) isoforms, thus promoting H3 trimethylation at lysine9 and chromoproteins recruitment at targeted sites. DNA methyltransferases are also present in KAP1 complexes. This finding correlates with the requirement for ZFP57 to maintain DNA methylation at imprinting control regions (ICRs). In this work we established the genome wide occupancy of ZFP57, along with associated chromatin modifiers KAP1, Hp1 and tri-methyl H3K9 and correlated it with the DNA methylation profile in murine embryonal stem cells (ESC). The data show that the majority of ZFP57 bound sites reside at DNA methylated non-imprinted loci, of which several encompass non-coding RNAs, implying a wider role for this factor in the shaping of the epigenome, notably at germ-line DNA methylated CpG islands and repeated retrotrasposons. Further, we show that ZFP57, while strongly expressed in ES cells and down regulated during differentiation, is also expressed at several sites during embryo development. The strong and sustained expression in the nervous system of the developing murine embryo is paralleled by association of the factor to ICRs extending its potential role beyond that of imprints maintenance at pre-implantation. We will report also on data suggesting a potential role for ZFP57 in the in vitro differentiation of ES cells toward the neural fate.