What is CRISPR/Cas9?

In recent years, the development of genome editing technology has revolutionised genomic research of both animals and plants. CRISPR/Cas9 is just one example of genome editing Repetitive DNA sequences, called CRISPR (Clustered Regulatory Interspaced Short Palindromic Repeats) were observed in bacteria with DNA sequences, ‘spacers’, between the repeats that directly matched viral sequences. Consequently, it was discovered that bacteria transcribe these DNA sequences to RNA following viral infection. This RNA then guides Cas9 nuclease (protein that cleaves DNA) to the viral DNA to cut it and therefore provide protection against the virus.

In 2012, it was demonstrated that RNAs could be designed to guide the Cas nuclease to any specific DNA sequence via complementary base-pairing. The ability to design specific guide RNA improves the likelihood that the cut will be made at the specific site and nowhere else in the genome. The double-strand break activates cellular DNA repair mechanisms. If no homologous repair template is present, error-prone non-homologous end-joining (NHEJ) pathway is activated, introducing random insertions/deletions or substitutions to disrupt gene function. In the presence of donor DNA template, homologous to sequence surrounding the double-strand break site, error-free homology-directed repair (HDR) pathway is triggered. This results in mutations that perform precise gene modifications such as deletion, mutation, or gene knock-in.

Mechanism of CRISPR

The mechanism is very versatile, being able to work quite well in all cell types. This one method of gene editing has significantly changed genomic research, considerably reducing the time and costs required and is now routinely used in mice. There are many potential applications to improve human health as well as development of novel crops that are so desperately needed to sustain food security. Adopted in nearly 20 crop species so far, CRISPR technology has the ability to increase disease resistance and tolerance to abiotic stressors that will increase with climate change.