Marsupial embryos lack the epigenetic reset seen in placental mammals

Biochemical ‘DNA methylation’ marks are found across the genome in vertebrate animals, but in the early embryos of placental mammals, such as mice and humans, they are largely erased in a ‘system reset’. Surveying DNA methylation in opossum embryos reveals that, in marsupials, such marks are retained. DNA-methylation marks remain stable in early-stage opossum embryos.