Written by Samantha O’Loughlin, Target Malaria
(This is the first of a series of six posts about common gene drive misconceptions)
In my work as a population genetics expert for Target Malaria, I travel to many meetings where I talk to people about our project to develop gene drive mosquitoes for reducing malaria in Africa. A few common misconceptions about gene drive come up again and again. This short series of myth-busting aims to address exactly that, contributing to an informed and open debate about this technology that can potentially help to solve many conservation and public health challenges.
The term ‘gene drive’ is rapidly becoming a household phrase, not just known by scientists but by people in all walks of life. Like most new technologies, especially those with high complexity, gene drive stirs up a lot of worries and suspicions in people’s minds. In this first of six myth-busting posts, I would like to start with some technical explanation: the difference between ‘gene drive’ and ‘CRISPR’: ‘Gene drive’ is not ‘CRISPR’ and ‘CRISPR’ is not ‘gene drive’. The gene editing system CRISPR hit the mainstream media last year when a Chinese scientist announced the birth of CRISPR edited babies. This blatant unethical misuse of the technology was for many people their first encounter with CRISPR. This is a shame, because when used responsibly CRISPR is a useful way of making very precise and accurate genetic changes, which in the past could have taken many years of hit-and-miss selective breeding.
CRISPR can be used in making gene drive organisms, but it is by no means synonymous with gene drive. The actual definition of a gene drive is a genetic construct (a stretch of DNA) that is inherited at a higher than usual rate. Normally genes are inherited by 50% of offspring, but in the case of gene drive this can be up to 100%. This means that the construct can spread rapidly into subsequent generations. Scientists observed this process happening in nature by a variety of different mechanisms, and recognised that it could be harnessed for applications in health and conservation.
One sort of gene drive works by making a special enzyme at the time when gametes (eggs or sperm) are being formed. The enzyme cuts DNA at a specific place and makes use of the cell’s own DNA repair mechanisms to copy itself into the cut site. There are many different types of these enzymes found in nature, of which CRISPR/Cas9 is just one. The reason that CRISPR has become so famous is that it makes it easier for scientists to accurately target a particular DNA sequence of an organism. CRISPR occurs naturally in bacteria, and examples of other similar enzymes that could be used in a gene drive are homing endonucleases, talens and zinc fingers, all of which come from nature.