Researchers at Seoul National University in South Korea have created the world's first transgenic dog.
Cloned beagle named Ruppy - short for Ruby Puppy - and four other beagles all produce a fluorescent protein that glows red under ultraviolet light.
The research team led by Byeong-Chun Lee created the dogs by cloning fibroblast cells that express a red fluorescent gene produced by sea anemones, reports New Scientist.
Team member CheMyong Ko of the University of Kentucky in Lexington said: "The next step for us is to generate a true disease model."
Scientists 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 week 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.
For researchers the challenge to create transgenic dogs is controlling where in the nuclear DNA a foreign gene lands.
To solve this problem, 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.
The study has been published in the journal genesis.