Ride the Tide: Observing CRISPR/Cas9 genome editing by the numbers

Targeted genome editing has become a powerful genetic tool for modification of DNA sequences in their natural chromosomal context. CRISPR RNA-guided nucleases have recently emerged as an efficient targeted editing tool for multiple organisms. Hereby a double strand break is introduced at a targeted DNA site. During DNA repair genomic alterations are introduced which can change the function of the DNA code. However, our understanding of how CRISPR works is incomplete and it is still hard to predict the CRISPR activity at the precise target sites. The highly ordered structure of the eukaryotic genome may play a role in this. The organization of the genome is controlled by dynamic changes of DNA methylation, histone modification, histone variant incorporation and nucleosome remodelling. The influence of nuclear organization and chromatin structure on transcription is reasonably well known, but we are just beginning to understand its effect on genome editing by CRISPR