Jun 26, 2012
Current developments in transgenic animals
Fish, pigs and mosquitoes: Genetic engineering in animals
No genetically modified animals are currently used in agriculture. However, there are a number of animals under development that have been genetically engineered to achieve faster growth rates or better disease resistance, and transgenic insects are being developed to combat plant pests and diseases.
Size comparison: The GM AquAdvantage salmon (background) and a conventional Atlantic salmon (foreground). The fish are the same age.
Source: Aqua Bounty Technologies
Enviropigs: GM pigs with improved phosphate utilization at the University of Guelph research institute.
Sorce: University of Guelph
The Aedes aegypti mosquito transmits dengue and yellow fever.
Source: University of California, Davis
Genetically modified fish: Accelerated growth and glowing colours
People have been developing transgenic fish (e.g. salmon, trout, carp and cichlids) for aquaculture for over 15 years, especially in the USA, Canada, Japan, Taiwan, Norway and the UK. However, the only GM fish close to being introduced onto the market are those with accelerated growth. Aqua Bounty, a US company, has applied to America’s Food and Drug Administration (FDA) for approval of its AquAdvantage salmon. This is a genetically engineered Atlantic salmon containing an additional growth hormone gene sourced from a Pacific salmon, and a special regulatory element which ensures that the hormone is produced even in the winter. This causes the fish to grow at about twice the usual rate.
Aquaculture and the optimisation of fish for fish farming have been booming for years. With wild fish populations suffering from overfishing, 50 million tonnes of fish and crabs are now farmed in this way.
Biotechnology and genetic engineering methods are being developed in addition to the conventional breeding methods, although none of these is currently used commercially. Besides growth acceleration, genetic engineering is being used to produce the following traits:
- Acceleration of muscle growth by inhibiting myostatin. This protein normally slows down muscle growth. Muscle mass can be increased by up to 20 per cent in these fish.
- Resistance to disease pathogens. Pathogens are often a problem in aquaculture because of the high population density.
- Cold tolerance: By transferring e.g. ‘antifreeze’ genes from fish in polar regions, farmed fish like salmon can be adapted to colder fish-farming regions.
Transgenic fish have to undergo a food safety assessment before a marketing authorisation can be issued. However, there is some debate about the potential negative environmental impacts in particular. Opponents fear that if the genetically engineered fish were to escape from the fish farms, they could displace wild populations as a result of their new traits.
The FDA has delayed approval of the fast-growing AquAdvantage salmon for more than ten years. The fish have been declared safe for human health, according to the FDA’s assessment, since the middle of 2010. According to an FDA report, they are no different from conventional salmon in terms of their nutrient and vitamin composition. Neither can the fish spread to wild populations because Aqua Bounty intends to market only sterile female fish. As an additional safety measure, the fish would only be farmed inland, and not in fish farms at sea.
For a short time in the summer of 2010 it looked as if the AquAdvantage salmon would be approved. First, though, the FDA held a public hearing, at which environmental and consumer organisations expressed their views. The hearing was accompanied by fierce public debates and protests. Experts then recommended carrying out further research before authorising the GM fish.
Transgenic zebra fish containing fluorescence genes are already commercially available for basic research. The fluorescent fish serve as model organisms for research into e.g. organ development. The fish are also available in the USA and Taiwan as glowing ornamental fish for private aquariums. Fluorescent angelfish and convict cichlids will probably be available from 2012.
Pigs that utilise phosphorus efficiently
Since 1999, scientists at the University of Guelph in Canada have been working on the development of a genetically engineered pig that can digest the phosphorus in its feed more easily. Pigs normally have difficulty digesting the phosphate contained in their feed grains. Most of the phosphorus is present in the form of phytate. Mineral phosphate or the enzyme phytase is therefore very often added to pig fodder to break down the phytate. However, this leads to high amounts of phosphates entering the environment through slurry and pig manure. High levels of phosphates in the drinking water make it unusable, and excessive phosphate levels in rivers and lakes lead to algae growth and secretion of toxic metabolites from the algae.
The genetically modified Yorkshire pig, called Enviropig, contains a bacterial phytase gene with a regulatory element taken from mice. This means that the pig produces the enzyme phytase in its salivary glands. When it chews, the enzyme is mixed with the feed, which means that phosphorus is released from phytate in the animal’s stomach. It can then digest the phosphorus efficiently. This means that the amount of phosphate excreted by the transgenic animals is up to 65 per cent lower than in conventional pigs. The pigs are also cheaper to feed.
In 2010, the Canadian authorities gave their approval for the development of a whole herd of these pigs to be used exclusively for research purposes and kept under strict confinement. The University of Guelph has also already applied for approval for use of the meat as food in the USA and Canada. A decision on this is not expected for a few years. The scientists see no problems from an animal rights perspective because the animals’ health indicators, such as vitality, growth and number of progeny, are no different from those of conventional pigs. The researchers conclude from this that the animals do not suffer in any way from the genetic modification.
The new gene could, the researchers believe, be transferred to other breeds through normal breeding methods. A narrowing of the genetic diversity of domestic pigs and higher susceptibility to diseases and other overbreeding phenomena would therefore not be expected.
Transgenic insects: Reducing harmful insect populations
There are also plans to use genetically engineered insects to combat plant pests and pathogens. The transgenic insects that have already been used in release trials are based on improved Sterile Insect Technology (SIT), reducing populations of harmful insects by releasing sterile insects from the same species into the wild.
SIT was first use on a large scale in the USA in the 1960s and 70s to combat a species of blowfly that had been causing huge problems for cattle. Millions of flies that had been bred in the laboratory and sterilised using radioactive irradiation were released on several occasions. When these flies mated with their wild relatives, there were no progeny. Using this method it was possible to wipe out the fly population almost entirely. However, sterile flies have had to be released every year since then, although on a smaller scale. The technology has been used many times since then, and is still used now, for instance to combat tsetse flies and fruit flies. In December 2010, Nature Biotechnology published the results of a successful four-year study that examined the repeated release of sterile cotton bollworm moths in Arizona as an alternative to the refugia
Scientists are now trying to insert a transgen into the genome of the harmful insect that will produce a substance that will kill the insects at the larval stage, instead of sterilising the insects using radioactive radiation. Oxitec, a British firm, has inserted a gene of this kind into Aedes aegypti, a species of mosquito that transmits dengue and yellow fever. In 2009 and 2010 the company conducted release trials with these mosquitoes on the Cayman Islands, a British territory. At the turn of the year (2010/2011), a release trial was conducted in a sparsely populated forested area in Malaysia. In both cases, environmental and citizen’s groups accuse Oxitec and the governments concerned of not providing the public with enough information.
Opponents warn that ecological niches resulting from the disappearance of insect populations could be occupied by other insects. This could, they claim, cause unforeseeable and uncontrollable changes to the ecosystem in question, such as the spread of new pathogens or new plant pests. Scientists developing transgenic insects argue that the insect pests are not usually native insects, and that the method is also species-specific and does not harm other insects.
Another, more recent, approach takes account of the fact that diseases like malaria, yellow fever and dengue fever are not themselves caused by the insects that bite people; the insects only transmit the pathogens. In 2012, scientists at the Institut Pasteur and the University of California succeeded in genetically modifying anopheles mosquitoes so that they produced antibodies that target the malaria pathogen Plasmodium falciparum. In the research conducted to date, plasmodia have not been able to develop and reproduce in these mosquitoes.
There are not yet any international regulations on the release of genetically modified insects. In 2006 a report was published by the International Atomic Energy Agency, which researches, among other things, the use of sterile insect technology in plant protection in collaboration with the Food and Agriculture Organization of the United Nations (FAO). The United States Department of Agriculture (USDA) published an opinion statement on genetically engineered plant pests in 2008. A comprehensive report on the status of research into transgenic insects and criteria for environmental risk assessments was produced in 2010 on behalf of the European Food Safety Authority (EFSA).