Development of a cloning technique to produce genetically-modified cats will help medical research in both cats and humans, scientists say.
US researcher Eric Poeschla produced three transgenic cats with cells that resist infection from a virus that leads to a feline form of AIDS, by inserting monkey genes — that block the virus — into feline eggs, or oocytes, before they were fertilised.
This method of genetic modification is simpler and more efficient than traditional cloning techniques, and results in fewer animals being needed in the process. The scientists also inserted jellyfish genes that made the modified cells glow green in some lighting — making it easier to see if the genetic engineering was successful and whether the effect was patchy or over most of the animal.
Dr Poeschla, of the Mayo Clinic in Rochester, Minnesota, reported his results in the journal Nature Methods and said that studies of the domestic cat had contributed to many scientific advances, including the present understanding of the mammalian cerebral cortex. “A practical capability for cat transgenesis is needed to realise the distinctive potential of research on this neurobehaviorally complex, accessible species for advancing human and feline health”.
Both humans and cats were afflicted with pandemic AIDS viruses that were susceptible to species-specific restriction factors, and one such set of genes — encoding rhesus macaque TRIMCyp — were inserted in a cat’s germ cells, with genetic material that may be passed to offspring. “The method establishes gamete-targeted transgenesis for the first time in a carnivore,” he said.
Feline immunodeficiency virus [FIV], is a close relative of HIV, the cause of AIDS in humans, and scientists hope that the use of genetically modified cats as models for the human disease will help research in both species understand how to confer resistance.
The UK Science Media Centre gathered reaction to the research, including the following comments:
Dr Robin Lovell-Badge, Head of Developmental Genetics, MRC National Institute For Medical Research, said:
“When carrying out research with animals, it is important to consider the most appropriate species for the questions to be addressed, and to adopt methods that are the least harmful, are efficient, and are likely to generate valuable data. The work on transgenic cats, by Wongsrikeao, Poeschla and colleagues, satisfies all of these requirements.
“They use a gene expressing green fluorescent protein, which, although it gives dramatic pictures, is important as it allows them to rapidly assess the success of the methods in live embryos and animals, while simultaneously introducing a gene (TRIMcyp) that may confer resistance to AIDS type viruses. This latter is the main purpose of the experiments. Cats are one of the few animal species that are normally susceptible to such viruses, and indeed they are subject to a pandemic, with symptoms as devastating to cats as they are to humans. Understanding how to confer resistance is therefore, as the authors point out, of equal importance to cat health as it is to human health.
“They needed to develop methods to introduce the genes, and they chose to use a lentivirus (in fact a type of virus related to that that causes HIV) to carry them. These are known from work in mice and other animals to be very efficient. The authors found that it was best to infect unfertilised eggs, which were then fertilised in vitro. Because they can obtain eggs and sperm from ovaries and testes of cats being neutered, and because they can study the early embryos in vitro, they could develop the methods without using any animals.
“They defined conditions that were very efficient (about 90%, which is extremely high) and used these to obtain several liveborn kittens – losing relatively few along the way. Both the fluorescent protein and the viral resistance gene were active in the animals, and importantly in their offspring, moreover they show that white blood cells from the animals are resistant to feline immunodeficiency virus (FIV).
“This is a methods paper, and the authors convincingly show that these work. Future experiments will address whether the resistance gene will work in whole animals and to establish ways to protect cats, and humans, from infection by SIV and HIV. For such experiments, mice are not such a good model – so a rare case where Tom trumps Jerry. The methods are of even broader importance, however. They allow genetic manipulation to be used as a tool to explore other aspects of cat biology, which may bring better understanding of neurobiology and vision and of ways to treat other problems affecting not just domestic cats, but all the wild cat species that we care so much about, but have endangered.”
Dr Laurence Tiley, Senior Lecturer in Molecular Virology, University of Cambridge, said:
“This technology can be applied to a wide range of species, for many of which there are clear applications and potential benefits. It will be interesting to see how enthusiastically this capability in cats is received and adopted by the HIV and neurobiological research communities and what other research opportunities it offers. A representative non-primate animal model would be a fantastic new tool for studying HIV pathogenesis.”
Professor Helen Sang and Professor Bruce Whitelaw, The Roslin Institute, University of Edinburgh, said:
“This report on a novel method for producing genetically-modified cats is an advance on previous studies using somatic cell nuclear transfer (cloning) in cats, where technical inefficiencies in the method limit application. This report describes the use of viral vectors to introduce genes into oocytes, a method that has already been shown to be very efficient in a range of other mammalian species, including pigs and sheep. The method described here is shown to be relatively effective in cats, reducing the number of experimental animals that are needed, although the embryological technologies are not yet as successful as in livestock.
“Cats are susceptible to feline immunodeficiency virus (FIV), a close relative of HIV, the cause of AIDS. The application of this new technology suggested in this paper is to develop the use of genetically-modified cats for the study of FIV, providing valuable information for the study of AIDS. This is potentially a valuable application but the uses of genetically modified cats as models for human diseases are likely to be limited and only justified if other models, for example in more commonly used laboratory animals, like mice and rats, are not suitable.”
Professor Ian Jones, Professor of Virology, University of Reading said:
“The findings from the Minnesota group demonstrate the ability to create transgenic cats. The genetic modification is in the germline so it is passed to offspring offering the possibility of producing a colony of identical animals. Although this is new for cats, it is has been done before for non-human primates and it remains to be seen which of these animal species will prove to be the more useful for human medical research, primates because of their similarity to man or cats because they are easier to breed. The authors suggest the technology will be useful for AIDS research but no data directly showing their utility is presented. What the authors do show is that cats can be made resistant to a natural cat virus, Feline Immunodeficiency Virus, which has some similarities to the AIDS virus. The data show very directly how a complex organism is simply the product of its genes and it is likely that transgenic cats will have a place in medical research going forward. However the benefit to AIDS research, while possible, is subject to more experimentation. The release of transgenic, perhaps disease resistant, cats, into the companion animal market is not discussed.
“The transgenic cat described was made resistant to virus infection leading to the possibility of breeding disease resistant animals in the future.
“This technology, which follows similar developments in the marmoset and monkey, may provide a useful animal model for a range of human diseases.”