by Nessa Carey
It’s not a complete free pass for all gene-edited varieties. It won’t apply to pest plants, or to genetic material from pest plants, reasonably enough.
One concern of many anti-GM activists in the past was that the expensive technologies required to produce GM crops would put too much power in the hands of multinational corporations. The criticism was also levelled that such corporations tended to focus their efforts on expensive commercial crops, not the ones that actually feed the poorest in society. Cassava, for example, is a staple for around 700 million people, but investment into improving this crop was a fraction of the amount spent on wheat. The latest ruling from the US Department of Agriculture may actually incentivise efforts to improve these neglected crops through gene editing.
That’s because some of the hurdles that made the original GM crops difficult and expensive to develop were the long and costly trials that were required, and the expensive regulatory applications. The latest ruling wipes out a lot of this expense, and coupled with the relative ease of gene editing, may democratise the production of better crops, bringing these orphans into the lab and then out to the fields.
The statement from the US Department of Agriculture made it very clear that promoting innovation was an important knock-on effect in its ruling. This in itself will stimulate more research by scientists wanting to improve crops. No one wants to work hard to create a better variety, only to find it can never be grown or eaten because of regulatory constraints.
All the signs were that the European Union would make a similar decision to the United States. This would represent a strong break with the past, as member states such as the United Kingdom had imposed draconian restrictions on GM crops, largely as a consequence of intense lobbying and campaigning by pressure groups. In January 2018 the European Court of Justice indicated that it was likely to decide that crops created by gene editing would not be covered by the regulations put in place in 2001 for GM plants.32
But in July 2018 the entire plant research community in Europe was appalled when the final decision was made. Plants created by gene editing are covered by the 2001 regulations.
Built within these European regulations is a quite extraordinary inconsistency. It is perfectly within the law for plant breeders to irradiate plants, or use chemicals, to create random mutations. If the effect of these mutations results in a useful characteristic, the breeders can propagate, produce and sell that plant. Let’s imagine one such mutation results in tomatoes with a sweeter flavour than usual. The irradiation or chemicals almost certainly caused other mutations in the plant, unintended ones that didn’t have any noticeable effect. It’s perfectly fine to grow and sell the resulting tomato plant and its fruits in Europe.
If, however, you use gene editing to create the one mutation that leads to the sweeter tomato, you can’t propagate, grow or sell the plant or its fruits in Europe. There is absolutely no difference at the DNA level between the mutation created by irradiation and the mutation created by gene editing, if we look at the relevant gene associated with sweetness. The plants derived from irradiation will likely have more mutations elsewhere in the genome than the edited plants, and there will have been no control at all over where they are or what they are.
The pressure group Friends of the Earth welcomed the ruling, but has stayed strangely quiet on the implicit support for irradiation this creates. So Europe is now in a looking-glass situation where a technology in which it’s impossible to control the outcome (irradiation) is preferred to one with exquisite fine-tuning (gene editing). It appears the law is as hopeless at understanding risk as most humans.
Notes
1. For a terrifying update on world human populations check out http://www.worldometers.info/world-population/
2. https://esa.un.org/unpd/wpp/
3. https://www.cia.gov/library/publications/the-world-factbook/geos/xx.html
4. http://data.un.org/Data.aspx?q=world+population&d=PopDiv&f=variableID%3A53%3BcrID%3A900
5. http://data.un.org/Data.aspx?d=PopDiv&f=variableID%3A65
6. https://www.cia.gov/library/publications/the-world-factbook/geos/xx.html
7. https://www.ons.gov.uk/peoplepopulationandcommunity/birthsdeathsandmarriages/lifeexpectancies/bulletins/nationallifetablesunitedkingdom/2014to2016
8. https://www.ons.gov.uk/peoplepopulationandcommunity/birthsdeathsandmarriages/lifeexpectancies/articles/howhaslifeexpectancychangedovertime/2015-09-09
9. http://www.fao.org/docrep/005/y4252e/y4252e05b.htm
10. House of Commons briefing paper 3336 on Obesity Statistics, 20 March 2018.
11. https://www.niddk.nih.gov/health-information/health-statistics/overweight-obesity
12. http://www.fao.org/save-food/resources/keyfindings/en/
13. Feng, Z., Zhang, B., Ding, W., Liu, X., Yang, D.L., Wei, P., et al. ‘Efficient genome editing in plants using a CRISPR/Cas system’. Cell Res. (2013); 23: 1229–1232.
14. Li, J., Norville, J.E., Aach, J., McCormack, M., Zhang, D., Bush, J., et al. ‘Multiplex and homologous recombination-mediated genome editing in Arabidopsis and Nicotiana benthamiana using guide RNA and Cas9’. Nat. Biotechnol. (2013); 31: 688–691.
15. Xie, K., and Yang, Y. ‘RNA-guided genome editing in plants using a CRISPR/Cas system’. Mol. Plant (2013); 6: 1975–1983.
16. Gil, L., et al. ‘Phylogeography: English elm is a 2,000-year-old Roman clone’. Nature (28 October 2004); 431: 1053.
17. Waltz, E. ‘Gene-edited CRISPR mushroom escapes US regulation’. Nature (21 April 2016); 532: 293.
18. Sánchez-León, S., Gil-Humanes, J., Ozuna, C.V., Giménez, M.J., Sousa, C., Voytas, D.F., Barro, F. ‘Low-gluten, nontransgenic wheat engineered with CRISPR/Cas9’. Plant Biotechnol. J. (April 2018); 16(4): 902–910.
19. Denby, C.M., Li, R.A., Vu, V.T., Costello, Z., Lin, W., Chan, L.J.G., Williams, J., Donaldson, B., Bamforth, C.W., Petzold, C.J., Scheller, H.V., Martin, H.G., Keasling, J.D. ‘Industrial brewing yeast engineered for the production of primary flavor determinants in hopped beer’. Nat. Commun. (20 Mar 2018); 9(1): 965.
20. http://ricepedia.org/rice-as-food/the-global-staple-rice-consumers
21. Miao, C., Xiao, L., Hua, K., Zou, C., Zhao, Y., Bressan, R.A., Zhu, J.K. ‘Mutations in a subfamily of abscisic acid receptor genes promote rice growth and productivity’. Proc. Natl. Acad. Sci. USA (5 June 2018); 115(23): 6058–6063.
22. Shrivastava, P., Kumar, R. ‘Soil salinity: A serious environmental issue and plant growth promoting bacteria as one of the tools for its alleviation’. Saudi J. Biol. Sci. (March 2015); 22(2): 123–31.
23. http://www.un.org/en/events/desertification_decade/whynow.shtml
24. https://www.theguardian.com/environment/2014/feb/09/global-water-shortages-threat-terror-war
25. Shi, J., Gao, H., Wang, H., Lafitte, H.R., Archibald, R.L., Yang, M., Hakimi, S.M., Mo, H., Habben, J.E. ‘ARGOS8 variants generated by CRISPR-Cas9 improve maize grain yield under field drought stress conditions’. Plant Biotechnol. J. (February 2017); 15(2): 207–216.
26. http://www.isaaa.org/resources/publications/briefs/49/executivesummary/default.asp
27. http://www.who.int/nutrition/topics/vad/en/
28. Humphrey, J.H., West, K.P. Jr, Sommer, A. ‘Vitamin A deficiency and attributable mortality among under-5-year-olds’. Bull. World Health Organ. (1992); 70(2): 225–232.
29. Ye, X., Al-Babili, S., Klöti, A., Zhang, J., Lucca, P., Beyer, P., Potrykus, I. ‘Engineering the provitamin A (beta-carotene) biosynthetic pathway into (carotenoid-free) rice endosperm’. Science (14 January 2000); 287(5451): 303–305.
30. http://supportprecisionagriculture.org/nobel-laureate-gmo-letter_rjr.html
31. https://www.usda.gov/media/press-releases/2018/03/28/secretary-perdue-issues-usda-statement-plant-breeding-innovation
32. https://www.theguardian.com/science/2018/apr/07/gene-editing-ruling-crops-plants
4
EDITING THE ANIMAL WORLD
Many of the problems faced by arable farmers
– how to keep their crops free of disease and produce great yields without the need for hugely increased inputs – have exact parallels in the livestock industry. So it’s no surprise that gene editing techniques are already under development to address some of these issues. In all these applications, the technology is used to create animals where every cell in their body has the edited DNA, and they will pass this on to their offspring. Creating the original edited individuals is tricky, as it relies on complex developmental biology approaches including implanting embryos into receptive females. But as long as the offspring are healthy, they will breed and pass on their edited DNA and new characteristics just as any animal would.
Essentially the gene editing is straightforward, but the rest of the process requires the same types of techniques that were used when the very first cloned mammal was produced. These are very specialist, so although lots of labs can edit the genomes of agricultural species in the test tube, only a much smaller proportion can go on to generate live animals from these laboratory experiments. The Roslin Institute in Edinburgh is one of the relatively small number that can, as it has the skilled staff and the facilities required for both gene editing and for cloning livestock. This isn’t surprising. The very first cloned mammal, Dolly the Sheep, was created at the Roslin Institute in 1996. She was cloned from a mammary cell, and named after the country music singer Dolly Parton. Technology and culture have moved on. The Roslin Institute is now headed by Eleanor Riley and one hopes that any future breakthroughs might result in rather less juvenile naming strategies.
There is a virus that affects pigs called Porcine Reproductive and Respiratory Syndrome Virus (PRRSV). It’s been a problem in the pig industry since the 1980s and in the US alone it causes losses of over half a billion dollars a year. If a pregnant sow is infected, all her piglets may be stillborn. Infected piglets that survive the pregnancy have severe diarrhoea and life-threatening respiratory infections. If a sow passes on the virus to her piglets in her milk, four out of five of them die. Animals that are infected after weaning grow slowly and don’t put on weight easily.
In order to wreak all this havoc, the virus has to find a way to get into the cells of the pig, especially certain specialised cells in the lung. It does this by hijacking a protein that is present on the surface of these cells, binding to a very specific region of it. Scientists at the Roslin Institute reasoned that they could use gene editing to change the region that the virus binds to. If the virus can’t bind, it can’t enter the cells, and it will die.
We can think of the region that the virus binds to as a damaged pearl in an otherwise flawless pearl necklace. A good jeweller can remove the one damaged piece and then re-link the ones on either side so that the owner still has a perfect pearl necklace. The scientists performed the equivalent gene editing manoeuvre to remove the virus-binding site on the pig protein, while leaving everything else intact and joined up.
The piglets they produced were healthy, and the protein carried out all its normal roles. Except PRRSV can no longer bind to it, so the pigs can’t be infected by, or pass on, this virus.1
The Roslin Institute is working with a breeding company called Genus PIC to create a pedigree herd of pigs that can be used as breeding stock. These will be able to transmit the resistance to their offspring, who will also be able to pass it on. The scourge of PRRSV could conceivably be wiped out.2
Pigs aren’t the only animals where gene editing is under development for the prevention of infectious diseases. Researchers at A&F University in Shaanxi in China have taken the first steps towards creating cattle that are resistant to bovine tuberculosis.3 It’s an area where we can expect to see many more announcements in the next few years.
Maxing the muscle
It’s great for livestock producers if animals can avoid infections. But they also need them to have other characteristics. Consumer demand for meat is increasing all the time, and particularly for lean meat. Meat producers want animals that can gain weight quickly, converting feed into lean protein efficiently, and getting to market quicker. Once again, gene editing has stepped up to the challenge.
Every year about a billion pigs are slaughtered in our seemingly unending appetite for pork and bacon. About half of these are in China so it’s perhaps no surprise that a research facility in China focused its gene editing efforts on this species. In doing so, they solved two problems for pig farmers simultaneously.
About 20 million years ago the ancestors of modern pigs were happily wallowing about in the tropical and sub-tropical climes of the prehistoric world. When you live in that kind of climate, you really don’t need a system to warm up quickly, as you’re probably at more risk of overheating. Perhaps as a consequence of this, the piggy ancestor lost a gene that is found in most other mammals. This gene is called UCP1, and it codes for a protein that can burn fat very quickly to generate heat. The protein is usually expressed in a tissue called brown adipose tissue. Pigs don’t have a functioning copy of UCP1, in fact they don’t even have any brown adipose.
But these days most pigs aren’t wallowing around in tropical or sub-tropical zones of the world. They are living in more temperate regions, and probably feeling the chill a bit. When they live somewhere particularly nippy, neonatal fatality can reach 20% in response to cold stress. Pig farmers have to spend a lot of money to keep pigs warm, and in some regions this can account for 35% of the overall energy costs of raising the animals.
Although gene editing can be used to make exquisitely delicate changes to the genome, it can also be used to insert whole genes into a cell. Gene editing has advantages over the traditional GM methods, even for a change as large as this. You can control exactly where in the genome the gene is placed, and you can create animals that contain only the extra gene and nothing else, no annoying additional sequences. Because of these advantages, the Beijing researchers used gene editing to put a UCP1 gene back into pigs. It wasn’t a trivial piece of work. They created more than 2,500 embryos in the lab, and implanted these into sows. Eventually twelve piglets were born, with functioning UCP1 genes. Once again, creating the edited embryos was essentially the easy bit. Production of living animals is still very difficult, and has success rates as low as when Dolly was produced in 1996.
The scientists bred the edited males once they matured and as expected, they passed the edited-in UCP1 on to their offspring. The edited pigs were able to maintain their body temperature in the cold much better than unedited pigs. There was also about a 5% drop in body fat, making this a positive double whammy all around.4
Pigs aren’t the only animal where farmers and consumers would like to have a larger amount of lean meat. However, most farm animals already have a functioning UCP1 gene so we can’t use this approach to increase their lean muscle mass. The alternative approach that is under development for a number of livestock species is to manipulate expression of a gene that acts as a brake on muscle development.
There is a common system of checks and balances that operates in mammals to regulate the size of the skeletal muscles. One set of signals encourages muscle growth, and another set holds it back. If we can find a way of tilting the scales in favour of the signals that encourage muscle growth, we should get chunkier, more muscled animals, with less fat. Gene editing is under development to do exactly this – tipping the scales by decreasing the brakes on muscle growth rather than trying to increase directly the signals that promote it.
A key gene in this process is called myostatin. The myostatin protein holds back muscle growth, and experimental studies using GM animals showed many years ago that decreasing the activity of this protein creates animals which are extraordinarily well-muscled. The animals have so much muscle and so little fat that they look quite bizarre – think Arnold Schwarzenegger in his late 1960s Mister Universe pomp.
Once again, gene editing is a much better approach than the original GM methods to produce individuals with very specific changes in their myostatin gene, and no other alterations. The technology
has already been applied to pigs, goats, sheep and rabbits,5 and seems to work particularly well in sheep, goats and rabbits. Importantly, the increased muscle growth occurs after birth.6, 7 This is significant because too much growth pre-natally can result in difficult deliveries.
One of the groups has speculated that this might be a useful approach to employ in Merino sheep. Merino wool is long and fine, and outdoor enthusiasts pay ridiculous amounts of money for socks and base-layers made from this fabric. But the sheep aren’t much use for meat production, as they lay down muscle too slowly and in too small an amount to be of commercial value. It should be perfectly feasible to perform gene editing on their myostatin gene to produce Merino sheep that still produce great wool but can also yield a decent amount of meat when they are finally slaughtered.
Another group has used a dual approach to turn average goats into ones with exactly this combined benefit. They edited both the myostatin gene and a gene that inhibits hair growth. Ten kids were born with the dual edits in their genes and the expected changes in gene expression. So far they haven’t published any pictures of the animals, but if all goes well as the animals mature, we may soon see very muscled, super-fluffy goats, looking like bouncers in Big Bird suits.8
Meat you can’t eat
It’s already very clear that it is going to be feasible to use gene editing to produce livestock with enhanced characteristics such as faster weight gain, leaner meat and resistance to disease. What is not at all clear is when, or even if, these will ever reach the consumer, or if the consumer will eat them.