GENOMIC manipulation, whether due to its connotations of ‘futuristic mad scientist’ or what appears as sheer complexity of patterns of heredity, is consistently associated with words such as ‘dangerous’ and ‘worrying’. However, since 2013, a new technique called clustered regularly interspaced short palindromic repeats, or more simply known by the acronym CRISPR, has turned up as the new kid on the block, and it is starting to make friends in the genetics world.
CRISPR is rapidly becoming one of the most exciting new opportunities for research scientists and doctors alike, a welcome alternative to the then-current protein-based gene-targeting methods known as TALEN and Zinc Finger that were customisable DNA-binding proteins requiring the generation of new proteins for every genomic target site. Instead, the new system uses sort lengths of the genetic material RNA to guide a restriction enzyme to the DNA target site.
arguably the most exciting breakthrough in modern medicine!
One could argue that CRISPR technology, unlike the development of antibiotic-resistant bacteria, is an evolutionary success story. Akin to humans having lymphocytes to minimise the effect of pathogens, bacteria and most Archaea adapted an acquired immune system based on CRISPR, acting as a defence against foreign, or non-self DNA.
For CRISPR to be used in genetic engineering two fundamentals are required: a short, synthetic length of RNA acting as a guide – RNA is a single-stranded polynucleotide – and a non-specific CRISPR-associated endonuclease called Cas9. Cas9 is an enzyme that cuts a twenty-nucleotide sequence of DNA, so long as this region is immediately upstream of a PAM, a Protospacer Adjacent Motif – a necessary binding site for the enzyme – and if the twenty base-pair sequence is unique to the rest of the genome.
In simple terms, if DNA was a road with a broken or faulty section , Cas9 would be the machinery that pulls up the road surface ready for fixing and the RNA would be the project manager.
Source: marius walter, wikicommons
Like a lock for a key, proteins, such as enzymes, have highly specific shapes which allow them to perform their function. Equivalent to putting the key in the lock to open the door, gRNA activates the Cas9 enzyme, such that there is a conformational change, whilst a “spacer” sequence of the gRNA remains free to attach itself to the DNA target. If conditions are right, within the DNA target region there will be double strand break. When such a break occurs, there is an automatic repair pathway, resulting in mutations of the DNA sequence which are small changes to the gene.
With such powerful techniques at our fingertips, it is almost unfathomable to think of the possibilities posed by this genome manipulation tool. Whilst its benefits may be seen immediately in treatments requiring the removal of cells from the patient before putting them back in, the most potential is with the editing of cells within the body itself, enabling a whole host of opportunities to treat conditions like liver disease, muscular dystrophy and even cancer.
CRISPR has turned up as the new kid on the block, and is starting to make friends in the genetics world.
Cleverly manipulating the fact that CRISPR is a feature of the acquired immune system of bacteria and archaea, earlier this year researchers at the Memorial Sloan Kettering Cancer Center, New York, modified immune cells, T lymphocytes, to express proteins on their surfaces that could both recognise and attack the proteins on the surface of cancerous cells, the corresponding antigens that fit complementary to the proteins on the surface of the T cells.
What makes using CRISPR so beneficial for such a treatment is the high specificity; researchers could deliver the gene required to a precise locus on the T-cell genome, reducing the chance of subsequent mutation, that could cause further tumours.
Where CRISPR could really make its mark in the future of health-care is by delivering gene manipulation like a conventional drug, straight to the site where it is required at.
For several decades now, scientists have been investigating how to deliver big molecules, such as the CRISPR machinery, to the correct sites. At Intellia Therapeutics of Cambridge, Massachusetts, researchers are looking into the use of fatty particles to deliver the CRISPR components to treat liver disease; similarly, they are working on a cure for hepatitis B, which also affects the liver.
Who would have thought that what could arguably be the most exciting breakthrough in modern medicine would originate from something that has actually been sitting quietly there all along: the not-so-humble bacteria.
To read more about genes and the leaps and bounds being made in the field try this where science editor Luke Smith explores revolutionary technology from Microsoft using DNA to store data!
