CRISPR, more formally known as Clustered Regularly Interspaced Short Palindromic Repeats, is a revolutionary take on gene-editing, which has transformed molecular biology and genetics. It has allowed scientists to edit the DNA (Deoxyribonucleic Acid) of living organisms with utmost precision, exceptional accuracy, efficiency, and ease.
The development of CRISPR began in the late 1980s, when a Japanese scientist — Yoshizumi Ishino — and his colleagues discovered unusual repeating sequences in DNA of the bacterium Escherichia coli (E. coli). These patterns, otherwise known as sequences, were later termed as CRISPR — initially thought to be a distinctive feature of bacterial genomes with little to no known function.
However, during the turn of 2005, researchers began to see the true significance of CRISPR. At that time, two researchers — Francisco Mojica and Ruud Jansen — recognized that these repeating patterns/sequences were often joined by unique ‘spacer sequences’. These ‘spacer sequences’ matched sequences from viruses that had previously infected the bacterium, which eventually led the duo to propose the scenario that CRISPR might play a crucial role in bacterial immunity against any viral infection.
Two years later, in 2007, an experimental breakthrough study — conducted by Philippe Horvath and his colleagues — showed that CRISPR had indeed performed as an adaptive immune system in bacteria, incorporating short segments of a viral DNA into their own CRISPR loci during a viral infection — which later functioned as a “memory” of all past infections. This “memory” could then be used to identify viral attacks and commence defense mechanisms by producing RNA (Ribonucleic Acid) molecules that targeted and destroyed the viral DNA.
The true potential of CRISPR, as a gene-editing tool, was discovered in 2012, when Jennifer Doudna and Emmanuelle Charpentier, along with other researchers, published a paper explaining a simple and versatile method for editing DNA with extraordinary precision, using CRISPR. This new method, commonly known as CRISPR-Cas9, involves harnessing the natural system of a bacterium’s immunity and repurposing it to target genome editing in other organisms — which includes humans too!
- The Cas9 protein;
- The ‘guide RNA’ (gRNA).
The Cas9 protein acts as a molecular scissor, capable of cutting DNA at specific locations. A short RNA molecule called a ‘guide RNA’ (gRNA), directs Cas9 to the required target sequence in the genome.
The development of CRISPR-Cas9 has sparked a huge revolution in genetic engineering, thereby offering a powerful tool for a vast range of applications — including basic research, biotechnology, agriculture, and medicine. CRISPR-Cas9’s simplicity, efficiency and versatility has made it widely adopted by scientists across the globe, leading to rapid advancement and innovations within various fields.
Since its introduction, researchers have continued to tweak and expand the CRISPR toolkit by developing new versions (variants) of the Cas9 protein with different properties, as well as other alternative CRISPR systems from other bacterial species. These efforts have led to the development of enhanced gene-editing tools with increased simplicity, efficacy, and flexibility.
On top of its ability in gene-editing, CRISPR has also been underscored in other applications, such as gene-regulation, epigenome editing, and live-cell imaging — further expanding the utility of CRISPR.
