Genome activation and architecture in the early mammalian embryo.

Over the last decade, our understanding of how the genome is packaged in three dimension within the nucleus has grown considerably. This is largely due to advances in high-throughput genomics assays to study higher order chromatin organization. Our knowledge of the structures adopted by the chromatin has far preceded our understanding of function and mechanism. An outstanding question has been how are such structures established. Recently, a suite of genomics assays has been adapted for low-input material, making it possible to apply them to the pre-implantation mammalian embryo. For the first time, chromatin topology and associations with the nuclear lamina have been described in the earliest stages of murine development. These studies have revealed the dynamics with which higher-order chromatin architecture is established in vivo. Additionally, they have yielded some intriguing findings that will pave the way for futures studies into the mechanisms underlying the establishment of three dimensional genome organization. Here, we discuss findings on how embryonic chromatin is dynamically organized within the nucleus throughout preimplantation development, and the outline a number of outstanding questions that will be exciting to address in the future.