Large-scale H3.1/H3.2 - H3K9me3 deposition defines the epigenetic signature of extraembryonic lineage cells [ATAC-seq]

The extraembryonic lineage in mammals is unique in its unipotent differentiation ability and gestation-limited development. Here we identified the epigenomic characters of mouse trophoblast stem cells (TSCs) focusing on the genome-wide enrichment of histone H3.1/H3.2 and H3K9me3. Comparative ChIP-sequencing (ChIP-seq) analysis of TSCs and embryonic stem cells (ESCs) revealed that the TSC genome uniquely contained large (over 1Mb) H3.1/H3.2-H3K9me3 domains in the intergenic regions. This feature was common to extraembryonic cells in mice and humans. Depletion of CAF1, a H3.1/H3.2 chaperone, led to downregulation of TSC marker genes such as Cdx2 and Elf5 and ectopic expression of Oct3/4, an ESC marker. Nuclear transfer cloning using TSCs resulted in extremely poor embryonic development, but removal of H3K9me3 from their genome resulted in birth of the first TSC-cloned mice. Thus, the signature of the extraembryonic epigenome is safeguarded by the H3.1/H3.2-H3K9me3 enrichment, which protects the genome from cell fate transition. Overall design: ATAC-seq analysis of ESCs and TSCs.