CRISPR/Cas System: An Introduction

The process of altering genetic code to modify DNA precisely and efficiently within a cell is known as genome editing. All techniques used for changing a gene in a cell are based on cutting of double-stranded DNA through DNA endonucleases at specific site. DNA nucleases used for genome editing are composed of programmable DNA binding domains to bind with target sequence followed by DNA cleavage domain to break double-stranded DNA that excites error prone non-homologous end joining (NHEJ) or homology-directed repair (HDR) at specific genome locations. Programmable nucleases enabled researchers to manipulate practically any genomic sequence, provided opportunities to create cell lines and animal models to study human diseases, and also promoting new possibilities of treating human diseases by gene therapy. Four genome editing technologies, meganucleases, zinc-finger nucleases (ZFNs), transcription activator-like effector nucleases (TALENs), and clustered regularly interspaced short palindromic repeats (CRISPR/Cas9) based on the above-mentioned principle have been developed so far and have been used successfully for the correction of disease-causing mutations, for addition of therapeutic gene and the deletion of specific genes from the specific sites in the genome. Genome editing revolutionized the scientific world and have intense impact on various fields of biotechnology, such as biopharmaceutical production, agriculture, creation of transgenic organisms and cell lines, regulation and function of the genome, etc. All four genome editing techniques, their history, principles, advantages, disadvantages, and applications, with a special focus on CRISPR/Cas, have been discussed in this chapter.