Various strategies of effector accumulation to improve the efficiency of genome editing and derivative methodologies

CRISPR-Cas9 is a sophisticated tool in which Cas9/sgRNA complexes bind to the programmed target sequences and induce DNA double-strand breaks (DSBs) enabling highly efficient genome editing. Moreover, when nuclease-inactive Cas9 (dCas9) is employed, its specific DNA-binding activity provides a variety of derivative technologies such as transcriptional activation/repression, epigenome editing, and chromosome visualization. In these derivative technologies, particular effector molecules are fused with dCas9 or recruited to the target site. However, there had been room for improvement, because both genome editing and derivative technologies require not only the DNA-binding tools but also the additional components for their efficient and flexible outcomes. For genome editing, DSB repair molecules and knock-in donor templates need to act at the DSB sites. Derivative technologies also require their various effector domains to be gathered onto the target sites. Recently, many groups have developed and utilized inventive platforms to accumulate these additional components to the target sequence by modifying Cas9 protein and/or sgRNA. Here, we summarize the strategies of CRISPR-based effector accumulation and the improved methodologies using these creative platforms.