27 Apr 2017

We need to talk about gene drives and gene editing

From Our Changing World, 9:06 pm on 27 April 2017

Imagine a New Zealand without introduced wasps, rats and possums, and a world where diseases such as malaria and heritable blindness have been eliminated.

This is a future that recent genetic breakthroughs could soon make possible – and scientists say we should be having a national conversation now about how willing we are to go there.

This brave new world will be possible through gene editing and gene drives – so what are they, how do they work, and what do they make possible?

Common wasp

Introduced European wasps are a significant problem in New Zealand beech forests - could a gene drive be a way of getting rid of them? Photo: CC BY 2.0 Sid Mosdell / Flickr

Gene editing

“Gene editing is a technology for changing parts of a genome,” says University of Otago geneticist Peter Dearden. "And it’s a very precise tool, which allows us to change individual base pairs in a genome that is made up of sometimes billions of base pairs."

The potential is enormous, says Dearden – we can change a gene, delete a gene or just turn it off.

Dearden points out that until now genetic modification has involved adding DNA from other organisms. Gene editing is different – “it’s merely changing the DNA of the organism in front of us.”

Precise gene editing has been made possible by the CRISPR/Cas9 system, which works like ‘molecular scissors’.

Another University of Otago geneticist, Neil Gemmell, compares it to word processing on a computer, and says it’s like replacing a single wrong letter in a sentence with the correct letter, or replacing a letter or a word in a way that changes the meaning of a sentence.

“So any traits [such as eye colour] that we know are governed by relatively simple genetic changes, we can edit those,” says Gemmell.

As an example, Gemmell talks about heritable blindness caused by a single-point mutation, which is an error in a single base pair. “There is now a programme in China targeted at the idea of using gene technologies to cure that.”

He says that at the moment this type of research is just being done with human embryos in the first few days of development, but in the future it could be a permanent fix that was passed down between generations.

And he says that because that future is already possible right now, “we need to discuss how that technology is used in humans right now, because in a year’s time we will be thinking about gene edited people.”

Brushtail possum

We are still a long way from being able to develop gene drives for possums - but it will happen. Photo: CC BY 2.0 G= / Flickr]

Gene drives

Gene drives are a way of spreading genetic change through an entire population.

Humans all have two copies of their genome in each cell. Both copies can be the same, but if the two copies of a gene are different, then that gene is heterozygous and your children have a 50% chance of inheriting either one of those genes.

“A gene drive,” says Dearden, “is a way of ensuring that every one of my children receive the same copy of my gene.” In their turn, all the offspring also pass on the same gene, and the gene quickly spreads through the population.

“A gene drive is a way of perpetuating gene editing within a genome,” says Gemmell. As an example, researchers are trying to use a gene drive to make all male offspring in mice, just by altering a single gene. If there are no females, it won’t take many generations before that mouse population collapses.

This would be a great form of pest control, but it’s also where it gets messy.

“Gene drives,” says Dearden “use gene editing, but they are also a normal genetic modification.” And the idea of genetic modification, or GM, makes many people throw their hands up in horror.

One way sign

Are gene drives reversible? Photo: CC BY-NC 2.0 Thomas Hawk / Flickr

Is a gene drive reversible?

A simple gene drive is irreversible, but researchers are investigating ways of limiting them so that they spread through most of a population but then cause their own extinction.

Gene drives in action

New Zealand is interested in using gene drives as part of its tool kit for Predator Free New Zealand 2050.

There is an international programme currently underway to create a gene drive to try and eliminate the mosquito-borne disease dengue, and it is also being considered for other diseases such as malaria. Neil thinks these programmes will offer the first international proof-of-concept for gene drives, but “New Zealand might not be far behind with respect to wasps and perhaps rodents.”

Despite all the hype, however, Dearden says we are not yet able to create gene drives in most organisms. “We are nowhere near that except in some lab animals …. in yeast and in Drosophila, the little fruit fly.”

Two gene drives have been published for mosquitoes, but they haven’t worked effectively, and they highlight a flaw in gene drives that apply to most organisms.

‘There’s a probability that these gene drives will be quite effective, but the view that they will be a miracle that will wipe out entire populations is not quite the case,” says Dearden.

Both Dearden and Gemmell say that apart from mice, there is little immediate prospect of gene drives being developed for the pest species that are of interest to New Zealand, namely wasps, rats, possums and stoats.

A national conversation about genetic technologies

This is a rapidly changing field, and to stay ahead of the game both men say we should be having a conversation as a country about how we might use these powerful genetic tools in the future.

The Royal Society Te Aparangi is working on a position paper to help start this and geneticists are wondering whether New Zealand should perhaps consider holding another Royal Commission, as it did for genetic modification in 2000, to consider potential risks and benefits.

Predator Free New Zealand 2050

In 2016 the New Zealand Government announced an ambitious plan to remove introduced rats, stoats and possums from New Zealand by 2050.

Here are a number of related stories that have featured on Our Changing World:

Conservation summit on Predator Free NZ 2050

The science of predator-free New Zealand

New Zealand leads world in island conservation

Trojan Females – a novel idea for pest control