More Evidence That We Have Much To Learn From Microbes

This month, I wanted to use blog to highlight another humbling example of a biotechnology breakthrough heralding from the ‘humble’ microbe. The specific example is that of CRISPR, an enzyme identified in microbes (prokaryotes) which possess a unique mechanism of action that scientists could potentially leverage for a wide range of roles. In brief, the CRISPR enzyme allows for the targeted editing of genomic material, and despite being first identified in microbes, the enzyme’s capabilities remain functional when handling eukaryotic DNA as well. To date, researchers have used CRISPR in a broad range of settings, but some of the most exciting have been those in medical fields; for example, scientists have recently repaired defective DNA in mice, curing them of specific genetic disorders. Plant scientists have also used CRISPR to edit genes in crops, raising hopes that they can engineer a better food supply. Some researchers are trying to rewrite the genomes of elephants, with the ultimate goal of re-creating a woolly mammoth. Writing last year in the journal Reproductive Biology and Endocrinology, Motoko Araki and Tetsuya Ishii of Hokkaido University in Japan predicted that doctors will be able to use CRISPR to alter the genes of human embryos “in the immediate future.”

Thanks to the speed of CRISPR research, the accolades have come quickly. Last year MIT Technology Review called CRISPR “the biggest biotech discovery of the century.” And there have been suggestions that the research team behind CRISPR’s discovery could be awarded a possible Nobel Prize in the future.

Even the pharmaceutical industry, which is often slow to embrace new scientific advances, is rushing to get in on the act. New companies developing CRISPR-based medicine are opening their doors. In January, the pharmaceutical giant Novartis announced that it would be using CRISPR technology for its research into cancer treatments, where it plans to edit the genes of immune cells so that they will attack tumors. CRISPR technology is seen as the potential second wave of DNA Editing technology to be used to treat cancer, following in the footsteps of Chimeric Antigen Receptor T-cell therapy (CAR-T) technology.

But to circle back to the specific science, how does CRISPR work? Microbes have been using these enzymes to edit their own DNA for millions of years, and today they continue to do so all over the planet, from the bottom of the sea to the recesses of our own bodies. In brief, the mechanism works as follows:

• The CRISPR-Cas9 system consists of two key molecules that can introduce a change into the DNA. These are:
• An enzyme called Cas9. This acts as a pair of ‘molecular scissors’ that can cut the two strands of DNA at a specific location in the genome so that bits of DNA can then be added or removed.
• A piece of RNA called guide RNA (gRNA). This consists of a small piece of pre-designed RNA sequence (about 20 bases long) located within a longer RNA scaffold. The scaffold part binds to DNA and the pre-designed sequence ‘guides’ Cas9 to the right part of the genome. This makes sure that the Cas9 enzyme cuts at the right point in the genome.
• The guide RNA is designed to find and bind to a specific sequence in the DNA. The guide RNA has RNA bases that are complementary to those of the target DNA sequence in the genome. This means that, at least in theory, the guide RNA will only bind to the target sequence and no other regions of the genome.
• The Cas9 follows the guide RNA to the same location in the DNA sequence and makes a cut across both strands of the DNA.
• At this stage the cell recognises that the DNA is damaged and tries to repair it.
• The DNA repair machinery in a cell is not 100 per cent perfect and often there will be a few bases that are lost around the site of the cut when it is repaired.
• This loss of bases represents a permanent change (mutation) in the genome and will affect the activity of the gene in which it is located. This may mean the gene doesn’t function properly or doesn’t function at all.
• Scientists can use CRISPR-Cas9 to target and mutate one or more genes in the genome of a cell of interest.