The new CRISPR-Cas system: RNA-guided genome engineering to efficiently produce any desired genetic alteration in animals

The CRISPR-Cas system is the newest targeted nuclease for genome engineering. In less than 1 year, the ease, robustness and efficiency of this method have facilitated an immense range of genetic modifications in most model organisms. Full and conditional gene knock-outs, knock-ins, large chromosomal deletions and subtle mutations can be obtained using combinations of clustered regularly interspaced short palindromic repeats (CRISPRs) and DNA donors. In addition, with CRISPR-Cas compounds, multiple genetic modifications can be introduced seamlessly in a single step. CRISPR-Cas not only brings genome engineering capacities to species such as rodents and livestock in which the existing toolbox was already large, but has also enabled precise genetic engineering of organisms with difficult-to-edit genomes such as zebrafish, and of technically challenging species such as non-human primates. The CRISPR-Cas system allows generation of targeted mutations in mice, even in laboratories with limited or no access to the complex, time-consuming standard technology using mouse embryonic stem cells. Here we summarize the distinct applications of CRISPR-Cas technology for obtaining a variety of genetic modifications in different model organisms, underlining their advantages and limitations relative to other genome editing nucleases. We will guide the reader through the many publications that have seen the light in the first year of CRISPR-Cas technology.