In this research proposal we want to evaluate the efficiency and usability of CRISPR-Cas9 for gene editing of mouse and human embryos (i.e. silencing of NANOG and CDX2). We will analyze the effect on early lineage segregation, and extend the culture period by using a recently established peri-implantation model and by the derivation of embryonic stem cells. The present project proposal will improve our understanding of how early human embryonic cells become more specialized during early development. Increasing our knowledge about the role of pluripotency genes and proteins, may provide new insight into the mechanisms of human embryo development. This will also promote advances in the treatment of infertility, or in developing biomarkers of embryonic health which might be used in clinical treatment. As the Med7 expert panel is specialized in research in the reproductive field, we believe this proposal fits in its scope.