Transposons and CRISPR: Rewiring Gene Editing

CRISPR-Cas is driving a gene editing revolution because of its simple reprogramming. Howe v e r , ofl'-target efl'ects and dependence on the double-strand break repair pathways impose important limitations. Because homology-directed repai r acts primarily in actively dividing cells, many of the current gene correction/replacement approaches are restricted to a minority of cel l types. Furthermore, current approaches display low efficiency upon insertion of large DNA cargos (e.g., sequences containing multiple gene circuits with tunable functionalities). Recent research has revealed new l i n k s between CRISPR-Cas systems and transposons providing new scafl'olds that might overcome some of these limitations. Here, we comment on two new transposon-associated RNA-guided mechanisms considering their potential as new gene editing solutions. Initia l l y , we focus on a group of small RNA-guided endonucleases of the IS200/IS605 family of transposons, which likely evolved into class 2 CRISPR efl'ector nucleases (Cas9s and Cas12s). We explore the diversity of these nucleases (named OMEGA, obligate mobile element-guided activity) and analyze their similarities with class 2 gene editors. OMEGA nucleases can perform gene editing in human cells and constitute promising candidates for the design of new compact RNA-guided platforms. Then, we address the co-option of the RNA-guided acti v i t y of difl'erent CRISPR efl'ector nucleases by a specialized group of Tn7-like transposons to target transposon integration. We describe the various mechanisms used by these RNA-guided transposons for target site selection and integration. Finally, we assess the potential of these new systems to circumvent some of the current gene editing challenges.