New paper helps unlock the mysteries of the mammalian placental epigenome

Placental epigenomics paperanimal_cartoon_cover_v1 A new paper featuring the work of Professor Janine LaSalle and Dr. Diane Schroeder from the Genome Center was published today in the journal PLOS Genetics. The paper, which features contributions from other scientists at UC Davis, the University of Texas, and Texas A&M University, describes the patterns of methylation in the genomes of cells taken from the placentas of a wide range of mammals (eight species including human, cow, and dog). DNA methylation is an important biological process in which some cytosine nucleotides (one of the four 'letters' of DNA) become chemically modified. This process differs from tissue to tissue, and leads to formation of genomic regions which can be classified as highly- or partially methylated. There are several known roles for DNA methylation, and it has been shown to be important for normal development of the placenta and embryo. By comparing the patterns of placental methylation across different species, Schroeder et al., could detect patterns that may be conserved across millions of years of evolution. They found that genes that were active tended to have relatively higher levels of methylation and this phenomenon was conserved across the species that they studied. Because one of those species was the opossum, which has a primitive placenta, the authors concluded that higher methylation in these active genes predated the existence of placental mammals.Placental epigenomics paper Commenting on the conservation of methylation patterns, Professor La Salle observed:
What is conserved across mammalian species is that expressed genes are more highly methylated than the surrounding genomic regions, and that this pattern of high gene body methylation is true for oocytes and preimplantation embryos. Understanding the methylation rules in early life is important for future studies in identifying epigenetic biomarkers in placenta (an accessible tissue usually discarded at birth) and in cancer, where the methylome is more similar to placenta than normal somatic tissues.
She also remarked on the nature of working with data from so many species:
This was the first time that my lab stepped out of our comfort zone of just working on humans and mice and it gave us a chance to collaborate with colleagues in the Vet School and Animal Sciences on finding placenta and oocyte samples from other species. It’s amazing what evolution can teach us about what’s important in the genome and epigenome!
Details of the full paper can be found on the PLOS Genetics website: