An essential prerequisite for normal embryo development is the activation of transcription from the new embryonic genome created at fertilization. This process, known as embryonic genome activation, occurs at a specified time after fertilization and is independent of the cell-cycle. This first round of embryonic transcription converts the transcriptome inherited from the gametes into one that encodes the totipotent state of the early embryo. Errors in the fidelity of this process compromises embryo development and post-natal health.
Several processes of remodeling of the embryo are required to achieve embryonic genome activation. These include: (1) remodeling nuclear chromatin from a transcriptionally repressive to a permissive state; (2) epigenetic reprogramming at the genic level to foster transcription of the totipotent transcriptome; (3) the assembly and nuclear localization of transcriptional machinery; and (4) the activation of the zygotic clock that coordinates these processes.
While many aspects of these processes remain unresolved, this presentation will review recent progress in our understanding of these essential requirements for embryonic genome activation. Gaps in our current understanding of this key developmental transition will also be highlighted.