A cloned beagle named Ruppy – short for Ruby Puppy – is the world’s first transgenic dog. She and four other beagles all produce a fluorescent protein that glows red under ultraviolet light.
A team led by Byeong-Chun Lee of Seoul National University in South Korea created the dogs by cloning fibroblast cells that express a red fluorescent gene produced by sea anemones.
Lee and stem cell researcher Woo Suk Hwang were part of a team that created the first cloned dog, Snuppy, in 2005. Much of Hwang’s work on human cells turned out to be fraudulent, but Snuppy was not, an investigation later concluded.
This new proof-of-principle experiment should open the door for transgenic dog models of human disease, says team member CheMyong Ko of the University of Kentucky in Lexington. “The next step for us is to generate a true disease model,” he says.
However, other researchers who study domestic dogs as stand-ins for human disease are less certain that transgenic dogs will become widespread in research.
Dogs already serve as models for diseases such as narcolepsy, certain cancers and blindness. And a dog genome sequence has made the animals an even more useful model by quickening the search for disease-causing genes. Most dog genetics researchers limit their work to gene scans of DNA collected from hundreds of pet owners.
Making a glowing dog
Lee’s team created Ruppy by first infecting dog fibroblast cells with a virus that inserted the fluorescent gene into a cell’s nucleus. They then transferred the fibroblast’s nucleus to another dog’s egg cell, with its nucleus removed. After a few hours dividing in a Petri dish, researchers implanted the cloned embryo into a surrogate mother.
Starting with 344 embryos implanted into 20 dogs, Lee’s team ended up with seven pregnancies. One fetus died about half way through term, while an 11-week-old puppy died of pneumonia after its mother accidentally bit its chest. Five dogs are alive, healthy and starting to spawn their own fluorescent puppies, Ko says.
Besides the low efficiency of cloning – just 1.7 per cent of embryos came to term – another challenge to creating transgenic dogs is controlling where in the nuclear DNA a foreign gene lands. Lee’s team used a retrovirus to transfer the fluorescent gene to dog fibroblast cells, but they could not control where the virus inserted the gene.
This would seem to prevent researchers from making dog “knockouts” lacking a specific gene or engineering dogs that produce mutant forms of a gene. These knockout procedures are now commonly done in mice and rats, and three researchers earned a Nobel prize in 2007 for developing this method, called “gene targeting”.
No bright future?
Ko is working to adapt a procedure used so far in pigs, cows and other animals to target genes in cloned dogs. His lab hopes to knock out a specific oestrogen receptor in dogs to understand the hormone’s effects on fertility.
The long lifespan of dogs and their reproductive cycle could make them more relevant to human fertility than mice, he says. “I think these dogs will be a very useful model for our research.”
Greg Barsh, a geneticist at Stanford University who studies dogs as models of human disease, says creating a transgenic dog is “an important accomplishment”, showing that cloning and transgenesis can be applied to a wide range of mammals.
“I do not know of specific situations where the ability to produce transgenic dogs represents an immediate experimental opportunity,” Barsh adds. But transgenic dogs will give researchers another potential tool to understand disease.
However, Nathan Sutter, a geneticist specialising in dogs at Cornell University in Ithaca, New York, says “transgenesis is labourious, expensive and slow”.
Add the expense of caring for laboratory-reared dogs and negative public perceptions and it could mean few researchers turn to transgenic dogs like Ruppy, he says: “it’s not on my horizon as a dog geneticist at all.”
Journal reference: genesis (DOI: 10.1002/dvg.20504)
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