Jaenisch’s team employed CRISPR to achieve the same feat in just one month, using a simple, streamlined protocol: microinjection of CRISPR components directly into one-cell embryos, followed by implantation of the gene-edited embryos into a female’s womb. Moreover, they showed that CRISPR could be programmed with not just one RNA guide, but multiple different guides, directing Cas9 to cut up and edit several DNA sequences in mouse embryos simultaneously. This kind of one-step, multiplex gene editing had never before been performed in mice.
