Placental Chromatin Enrichment and Sequencing

Placental chromatin isolation and sample preparation was performed as described previously^{26 (link)}. Briefly, chromatin was isolated from halved placentas following six 5 min rounds on sonication on ice, using Dynabeads Protein G (Life Tech) and an H3K27me3 antibody (Millipore 07–449; 1:15). Multiplexed libraries were prepared from 10 ng of chromatin using the Illumina TruSeq ChIP Sample Preparation Kit. Libraries were sequenced (50-bp single end) on an Illuminia NextSeq500; fastq files were aligned to the genome using Bowtie2^{58 (link)}, enriched peaks relative to input for H3K27me3 were calculated using HOMER^{59 (link)}, and these peak counts were then used for subsequent analyses in DESeq^{60 (link)}.