Transcriptional and epigenetic control in mouse pluripotency: lessons from in vivo and in vitro studies.

Pluripotent cells were first derived from mouse blastocysts several decades ago. Since then, our knowledge of the molecular events that occur in the pre-implantation embryo has been vastly progressing. The emergence of epigenetics has revolutionized stem cell and developmental biology and further deepened our understanding of the underlying molecular mechanisms controlling the early embryo development. In particular, the emergence of massive parallel sequencing technologies has opened new avenues and became indispensable tools in modern biology. Additionally, development of new and exciting techniques for genome manipulation (TALEN and CRISPR/Cas9) and in vivo imaging provide unique opportunities to perturb and trace biological systems at very high resolution. Finally, recent single-cell - omics combined with sophisticated computational methodologies allow accurate, quantitative measurements for deconvolution of cellular variation in complex cell populations. Collectively, these achievements enabled the detailed characterization and monitoring of various cell states and trajectories during early stages of embryonic development. Here we review recent studies of the transcriptional and epigenetic changes during very early stages of mouse embryo development and compare these with pluripotent cells grown in vitro under different culture conditions. We discuss whether the in vitro cell states have an 'epi-phenocopy' in the embryo and refine our understanding of the circuitries controlling pluripotency and lineage commitment during early stages of mouse development.