Genome organization and stability in mammalian pre-implantation development.

A largely stable genome is required for normal development, even as genetic change is an integral aspect of reproduction, genetic adaptation and evolution. Recent studies highlight a critical window of mammalian development with intrinsic DNA replication stress and genome instability in the first cell divisions after fertilization. Patterns of DNA replication and genome stability are established very early in mammals, alongside patterns of nuclear organization, and before the emergence of gene expression patterns, and prior to cell specification and germline formation. The study of DNA replication and genome stability in the mammalian embryo provides a unique cellular system due to the resetting of the epigenome to a totipotent state, and the de novo establishment of the patterns of nuclear organization, gene expression, DNA methylation, histone modifications and DNA replication. Studies on DNA replication and genome stability in the early mammalian embryo is relevant for understanding both normal and disease-causing genetic variation, and to uncover basic principles of genome regulation.