High-resolution analysis of the human placental DNA methylome in early gestation

We communicate high-read-depth bisulfite sequencing analysis of the chorionic villus (CV) DNA methylome from samples obtained between 11 and 13 weeks gestation and samples of gestationally age-matched maternal blood cells (MBC).

This was achieved through solution-phase targeted region capture (84 Mb) of bisulfite converted human DNA.

We identified biphasic distribution of methylation in CV and MBC genomes. We found greater numbers of intermediate methylated sites (20%-80% methylated) in CV and greater number of high methylation sites in MBC and investigated distributions of these in promoters, introns, exons, CpG islands, CpG islands shores, and enhancers. We identified differentially methylated sites distinguishing CV and MBC. These are less likely to occur in CpG islands (CGIs), particularly those that exist outside promoters, exons, and introns. We found that gene promoter and gene body methylation patterns are associated with mRNA transcriptional profiles in CV. Despite the relative hypomethylation of CV genomes, we found that these contain DM regions that are more likely to be hypermethylated in CV relative to MBC.

Our data provide novel insight into the structure and organization of the CV epigenome, which may inform future studies of placental biology and noninvasive prenatal phenotyping.