Chimeric proteins to improve CRISPR-Cas9 gene targeting

Abstract

The discovery of Clustered Regions of Interspersed Palindromic Repeats (CRISPR), a defence system against viruses found in bacteria, launched a new era in gene targeting. The key feature of this technique is the guiding of the endonuclease Cas9 by single guide RNAs (sgRNA) to specific sequences, where a DNA lesion is introduced to trigger DNA repair. The CRISPR/Cas9 system may be extremely relevant for gene therapy, but the technique needs improvement to become a safe and fully effective tool. The induced DSB is repaired by one of two pathways, the error-prone NHEJ or the high-fidelity HDR. Shifting the repair of the DSB to HDR is challenging, given the efficiency of NHEJ. In this thesis, novel engineered proteins and shRNA-mediated knock-down approaches are presented to increase knock in efficiency, focused on key features influencing the choice of the repair pathway: the stage of the cell cycle, the nature of the DSB end and the interplay between NHEJ and HDR proteins. Chimeric proteins favouring repair by HDR are described and the strategy for NHEJ suppression was successfully demonstrated. These approaches have been tested separately. The preliminary results are encouraging to pursue this line of research and eventually publish a genome editing protocol combining the different approaches.