Tamed

by Alice Roberts

  While the ovulated hen’s ovum measures about 2.5cm across, a human egg is just 0.14 millimetres in diameter. But that’s actually a very large cell, compared with the size of other cells in the body. It contains enough cytoplasm – the stuff inside the cell – to get embryonic development under way after fertilisation. The fertilised human egg is able to divide itself up into a ball of cells, without actually growing in size. In comparison, the hen’s unfertilised egg is huge. It’s the size of the yolk in a laid egg – and that’s exactly what most of it is. One huge cell, stuffed full of yolk nutrients to support the developing embryo, with a tiny, tiny bit of cytoplasm at one end – it’s there on your breakfast plate if you bother to look for it. In that cytoplasm are the chromosomes that represent the female genetic contribution to the embryo. The male genetic component is delivered to the egg by the sperm. And that’s when things start to get interesting. Whereas mammal eggs divide slowly, with the first cell division, into just two cells, complete after approximately twenty-four hours, the fertilised chicken egg doesn’t hang around. By the time the hen lays the egg – twenty-four hours after fertilisation – a disc of around 20,000 cells has already formed. If you opened up the egg immediately, you’d see it – a whitish disc on one side of the yellow egg yolk. If the laid, fertilised egg is kept nicely warm, the blastodisc (those 20,000 cells) continues to grow, multiply and develop into a chick embryo.

  At just four days after being laid, the blastodisc has already rolled itself up into what will become the body of the chick. The developing eye is clearly visible and the chick embryo’s heart is already beating. (The human embryo only reaches an equivalent stage of development a full four weeks after fertilisation.) A network of blood vessels has also developed around the chick embryo by this point, reaching out around the yolk of the egg. If you shine a light through a four-day-old, fertilised and incubated hen’s egg, you can see these blood vessels quite clearly, radiating out like spidery red tendrils from a central red spot which is the embryo itself. If you were able to make an opening in the egg, and insert a tiny needle into one of those embryonic blood vessels at this stage, you’d be able to draw out a minute sample of blood. Within that sample there will be early blood cells – but also some extremely important stem cells. These are the primordial germ cells – which would eventually settle in the gonad of the developing chick, ready to make eggs or sperm, depending on the sex of the chicken.

  Mike McGrew is working on taking blood from slightly younger embryos, only two and a half days old. At this stage, just a tiny sample contains 100 germ cells. The next trick he’s pulled off is to get the cells to grow in culture, away from the embryo, for months and months. That gives him the opportunity to edit their genes – using a new technique to make precise modifications, cutting out some pieces of DNA and splicing new ones in.

  Having made those adjustments, the primordial germ cells can then be injected into a chick embryo that has already been genetically manipulated so that it doesn’t produce any of its own germ cells. Amazingly, development then proceeds as normal – the genetically altered primordial germ cells migrate to the ovary or testis of the developing chick. When that chick hatches and grows up into a hen or cockerel, that bird will be producing eggs or sperm which all contain the adjusted DNA.

  The instrument which is allowing the geneticists to make precise adjustments to genomes is called CRISPR – the sharpest new tool in the genetic-engineering, neo-Neolithic toolbox. It’s much more refined than the traditional, viral vector method, but it’s also borrowed from nature, and based on years of painstaking research into the ways in which viruses and bacteria wage war on each other.

  Some bacteria have a clever method of defending themselves against viral attack – a system which essentially provides them with immunity against viruses. When bacteria are exposed to viruses they copy a section of the viral genetic code into their own genome. It seems foolish – aiding and abetting the virus in this way – but it’s not. It means they can ‘remember’ the pathogen and fight it off effectively the next time. The piece of pathogen DNA is flanked by strange, repeating sections of genetic code: bookmarks for the bacterium. These bookmarks that are known as CRISPR: Clustered Regularly Interspaced Short Palindromic Repeats. When the bacterial cell becomes infected, it looks up the bookmark and reads the short section of pathogen DNA – copying that sequence, using a slightly different molecule, RNA (which stands for ribonucleic acid, whereas DNA is deoxyribonucleic acid). That copy, the RNA ‘guide’, links up with a DNA-cutting enzyme in the bacterial cell which acts like a molecular pair of scissors. The RNA guide homes in and locks on to DNA arriving with an invading pathogen – and the enzyme neatly cuts it up, disabling it. So, if you wanted to make a very precise cut in a piece of DNA, you can specify your own target by creating an RNA guide – then giving it to the scissor-enzyme, to make a snip exactly where you wish. You can make as many cuts as you like, where you like.

  The potential applications for this new tool are myriad. With this new gene-editing technology, it’s possible to snip out particular genes much more precisely than ever before, creating a ‘knockout’ embryo. As this embryo develops it will reveal what the function of that gene would have been, by demonstrating what happens in its absence. Understanding embryological development better will help us tackle diseases in the future – not only in chickens, but in vertebrates more generally, including in us humans. CRISPR could also be used therapeutically – to remove damaged DNA in living organisms. It’s already been employed, in the lab, to remove cancer-causing pieces of viral DNA from human cells. In fact, the technique is so refined that it can be used to snip out a single base pair – effectively just one nucleotide ‘letter’ on a chromosome – from a genome. But it’s not all about removing DNA – CRISPR makes it possible to precisely remove a section of DNA, and to splice in another. Cells are never happy about having their DNA snipped up. Molecular machinery will swing into action to repair the damage. The cell will usually look at the other chromosome in the pair to help it reconstitute the damaged DNA. But you can make a suggestion to the cell, by introducing your own piece of template DNA for it to copy instead. This has already been done – in the lab – to modify yeasts to make biofuels, to alter crop strains, to engineer mosquitoes resistant to malaria. The American Association of the Advancement of Science branded this new gene-editing technique the scientific breakthrough of the year in 2015. The field is moving fast – the range of potential applications is dramatic – but ethical questions abound.

  Helen Sang has been studying vertebrate development and using genetic-modification techniques for more than forty years. She’s still interested in uncovering the fine detail of embryological development, but she’s also worked on chickens to genetically modify them to produce valuable proteins – things they never normally manufacture. Helen had done this with hens’ eggs and human interferon, a protein made naturally in the human body but also used as a drug to help fight viral infections. The egg white that hens make contains the protein ovalbumin. If you take the regulatory sequence, the ‘on-switch’ for ovalbumin, and join that up with the human interferon gene, you can stick that package into hens and they’ll start to make interferon alongside ovalbumin. So it’s possible to modify chickens to make it easier to study their development, as Adam had done with his green fluorescent protein in the lymphoid cells, and it’s also possible to get chickens to make other useful proteins for you, in their eggs – such as that interferon.

  But in recent years, the focus of Helen’s research at Roslin had moved to looking at ways of modifying the chickens we eat. She was interested in something of immediate, real world relevance – promoting disease resistance in chickens. She was excited by the potential of CRISPR to achieve results precisely and quickly. She explained how it could work. You’d start by screening birds for disease resistance – to avian flu, for example – and then looking for genes associated with that resistance. That gene may only differ by a few nucleotides from the s
equence in another bird, but those tiny differences can be crucial. Having identified a useful gene, you can use CRISPR to cut out the equivalent in another bird, and then replace it with the one you know will be beneficial. Using the technique in this way, you’d simply be spreading a genetic variant which already existed in chickens through a flock, without having to go through the laborious process of selective breeding. But of course there is another possibility: as well as introducing a variant of a gene from the same species, the same technique can be used to bring in a gene from a separate species. ‘We can move genetic information from anywhere to anywhere,’ Helen said, quietly in awe of the technique. ‘I think that’s a possibility which causes more worry – the idea that you move genetic information across the species boundary,’ I observed. ‘Well, it’s all DNA,’ replied Helen, ‘and anyway we know that DNA gets around – you can find things in us which have come in from other species.’ And that’s true, you can – especially from viruses, which love to go sticking their genetic oar into other genomes.

  In fact, it isn’t just naturally occurring genes that geneticists could move from one species to another; they can now make entirely novel, artificial genes. It sounds extraordinary, but it’s already bearing fruit in chickens, if that’s not too mixed a metaphor. Geneticists are already exploring this avenue, designing artificial genes – specifically designed to throw a spanner in the works of viral replication – from scratch. One promising gene has induced chicken cells to make a small RNA molecule which caused problems for viruses, but Helen’s experiments have shown that it doesn’t confer complete resistance – there’s clearly still much more work to be done in the lab before a geneedited, flu-resistant chicken is a reality. What I was convinced of at Roslin is that it’s certainly on its way, and not too far over the horizon.

  Working on aspects of biology which have such obvious benefits as disease resistance may encourage acceptance of the use of genetic modification in livestock and crop development. Helen thought that CRISPR itself may help to allay some fears. The precision of the technique meant that you could insert a gene somewhere where it wouldn’t derail any other operations in the cell – geneticists call such locations ‘safe harbours’ – while at the same time maximising its chances of being read, or expressed, by cells. With traditional modification, using viral vectors, you couldn’t predict where the gene would be inserted – though of course you can check afterwards. But with CRISPR, you can go straight in and make sure that gene is placed exactly where you want it.

  Helen was eloquent on public perceptions of GM. She believes that the debate has been hijacked by certain lobbying groups with rigid agendas, and that the public in general isn’t being given the chance to choose: to accept the technology – or not. ‘At the moment, GM isn’t a choice. You can’t go to a supermarket and buy a GM chicken. We don’t sell anything that’s genetically modified. It’s very unusual to have a whole technology which is excluded, rather than giving people a choice.’

  Helen told me that when she first started working in this area of science, and told people what she was doing, the reaction was generally positive – ‘They thought it was really neat, a great idea. Then suddenly it became anathema as far as food goes.’ I asked her if she thought that it all went back to the debacle that ensued when the biotech company Monsanto tried, controversially, to introduce its GM soy to Europe in the 1980s – and she does think that this played a significant role. Somehow, the debate over GM became hopelessly entangled with concerns about the domination of big, multinational companies. But this is something that worries Helen, too. ‘There are many things that I would be just as concerned about as somebody from Friends of the Earth, about where our food is coming from,’ she said, somewhat surprisingly, ‘but I think it’s a complete distraction to focus on GM. It’s a technology which has something to contribute. And we should be able to find a way of allowing that to happen, and allowing people to make their own choices. GM’s been used to epitomise bad, big business – whereas it’s actually just another tool.’

  Not only is the conflation of GM and big business unhelpful to working out how, as a society, we feel about this technology, Helen also believes that it’s become a positive distraction from the real issues facing us about the future of food production. ‘There’s a smaller and smaller number of very large companies controlling food production. That’s not a scientific problem – it’s a political and economic one,’ she explained. ‘And it’s a tricky one. You have to accept that it’s been very efficient. We do need to feed a lot of people. But we need to have more sophisticated conversations about how we can take advantage of those efficiencies while protecting the environment and feeding the financial reward back to society.’ In some ways, the concern over GM, and the ensuing, incredibly tight regulations placed on this technology, only makes that problem worse. The cost of meeting the regulators’ demands is so high that it is effectively prohibitive. Only big multinationals can really afford to invest in GM – it’s stifling innovation and placing it solely in the hands of a small number of huge companies.

  I asked Helen a difficult question: what did she think might happen over the next decade? Was it possible that GM would become more acceptable? She thought so. Younger people seem less likely to reject the idea out of hand. ‘But then, in the States, we’re seeing a backlash,’ she said. There have been moves in some US states to enforce labelling on GM foods – something they’ve never done previously. The idea of labelling something ‘GM’ is strange in many ways, especially if you’re only going to include enzyme-induced modifications, and not the ones created by irradiating organisms. There’s no risk to human health from eating GM food, even if you disagree with the methods used to produce it. And what does a ‘GM’ label tell you anyway? To be even moderately informative, it needs to describe what the modification is, and what its consequences are. ‘But on the other hand, if people want to know, then they have the right to know,’ said Helen. ‘It’s a really tricky argument.’

  We discussed Golden Rice – a GM form of rice with enhanced levels of vitamin A, designed to combat dietary deficiency – which has provoked such a variable response from the public. Some accept it as a genuine philanthropic effort, and believe that it could really help to reduce vitamin A deficiency, particularly in some of the poorer countries of the world. Others see it as merely a poster child, something the ‘GM industry’ has bought into, simply as a tool of persuasion – the acceptable face of GM and the thin end of the wedge. It seems entirely reasonable to distrust the motives of some large companies who are trying to sell more of their own herbicide off the back of selling GM crops. But perhaps we should be more trusting of efforts to help the poorest farmers and communities – as Bt Brinjal, a disease-resistant GM aubergine produced as an entirely not-for-profit exercise, has already done. ‘If we want to be producing food efficiently and sustainably, we shouldn’t cut ourselves off from some of the ways we can do that,’ Helen concluded.

  Perhaps it’s too easy to be cynical. It seems a shame that this technology wasn’t first developed and implemented by universities or not-for-profit enterprises. I have no doubt that there wouldn’t have been such a backlash and a collapse of trust if that alternative historical scenario had played out. But genetic modification has become so tainted by its connection with big business and questionable motives. It’s hard to shake that off – even where research is now being carried out by publicly funded, university research institutes.

  For Mike McGrew at the Roslin Institute, one of the most exciting prospects for gene editing, if it is ever allowed out of the lab into the real world, lies in its potential for promoting disease resistance in farmed animals, particularly in developing countries. ‘We’re working with the Bill Gates Foundation in Africa,’ Mike told me, with undisguised pride. ‘Anything that would make these commercial chickens survive and thrive better over there, and actually lay eggs in a non-ideal climate, would be such a huge benefit.’ But Mike’s not just interested in the
potential of these new techniques for breeding better commercial poultry, particularly in Africa, but in possible applications amongst wild birds too.

  ‘This is the thing I really care about: conservation biology. Think about the honeycreeper that lives on the Hawaiian Islands. We effectively brought in avian malaria to Hawaii, and the native honeycreeper has no resistance, because it’s never seen avian malaria before.’ All the birds living at lower altitudes have been killed off. The only ones left are those high up in the mountains, where it’s cooler and the mosquitoes don’t survive. But now, with global warming and rising temperatures, the mosquitoes are starting to reach higher altitudes, placing honeycreepers under increased threat of extinction. ‘So imagine if we were smart and we knew the genes responsible for resistance to avian malaria,’ Mike mused. ‘Could we could go into these wild populations, edit their genes, then release them? So there would now be disease resistance and the honeycreepers would thrive. Just imagine doing that.’

  Mike understands the antipathy to GM when it’s focused on food in developed countries. ‘But if you’re able to do something useful for the human race, for the planet – there are a lot of different things we can use this technology for – I think people will start to recognise and welcome the potential.’ He spoke with real passion, but without any hype. ‘We need more education,’ he said. ‘Not fake news on the internet or in tabloids. People think DNA is the essence or the soul of an animal – and we’re changing its soul. But when they understand what DNA actually is, and what this technology is, they stop being scared.’ And yet it seems unlikely that the first GM chickens will hatch out of the broiler industry. The commercial firms are too sensitive to lobbyists. And with the Food and Drug Administration in the United States now keen to label any genetic modification – even to a single base pair – as requiring the same level of regulation as a new drug, the technology is unlikely to take off in America. So where did Mike think the first genetically modified chickens would finally enter the human food chain? ‘It’ll be China,’ he said. ‘China without a doubt. They have the genetics. And they have bird flu.’ If I was the betting type, I’d also be putting money on that immediately. I’m sure Mike will be proven right. If not in 2018, then very, very soon.