At Last: Gene Editing in Human Embryos to Understand Human Development Albert Ruzo, Ali H. Brivanlou  Cell Stem Cell  Volume 21, Issue 5, Pages 564-565 (November 2017) DOI: 10.1016/j.stem.2017.10.008 Copyright © 2017 Terms and Conditions

Figure 1 Therapeutic versus Non-therapeutic Use of Gene Editing in Human Embryos (Top) In their attempt to maximize the efficiency of correction of a disease mutation in human embryos, Mitalipov and colleagues (Ma et al., 2017) injected Cas9 protein and sgRNA as early as possible, which is together with the sperm, at the time of fertilization. With this approach, they were able to correct 45% of the mutant embryos completely, with no mosaicism and no detectable off-targets. In the remaining 55% of the embryos, the gene was destroyed by non-homologous end-joining (NHEJ) repair mechanism, which renders it useless. (Bottom) In a recent report by Niakan and colleagues (Fogarty et al., 2017), they harnessed the highly efficient NHEJ mechanism to ablate the OCT4 gene in ∼90% of the injected embryos and demonstrated that OCT4 has different functions in human embryogenesis compared with other animal models. Cell Stem Cell 2017 21, 564-565DOI: (10.1016/j.stem.2017.10.008) Copyright © 2017 Terms and Conditions