Fluorescent Mice Herald Gene-Transfer Breakthrough

D.L. Parsell
National Geographic News
January 11, 2002

By using an innocuous virus derived from HIV, scientists at the California Institute of Technology have developed a new way of giving animals genes from other organisms to produce specific traits.

Termed transgenic animals, they are important to progress in biological research and have a wide range of potential benefits in human health, agriculture, and many other fields.

Animals that have been "engineered" to acquire certain medical conditions, for example, serve as good surrogates for studying human diseases and testing potential treatments and cures. In the future, cows might be given genes that enable them to produce milk containing therapeutic human proteins, or there may be transgenic chickens that can produce eggs low in cholesterol.

Since the first transgenic animal, a mouse, was created more than two decades ago, different methods of development have been tried, but met with mixed success. The new method announced by the researchers at Caltech has some advantages over other techniques.

Today, transgenic animals are generally created by injecting "foreign" genes into the nucleus of animal cells—a procedure that is costly and requires a high degree of precision and expertise. The new technique entails using a powerful virus, much like the one that causes AIDS, to deliver the genes into the cells and insert them into an animal's genome.

"It's surprising how well it works," said David Baltimore, a Nobel Prize-winning biologist who led the research team. "This technique is much easier and more efficient than the procedure now commonly in use, and the results suggest that it can be used to generate other transgenic animal species."

Green Glow

The development of the new method, which was reported January 10 on the Web site Science Express, drew on Baltimore's pioneering research in the genetic makeup of viruses. Baltimore is now the president of Caltech.

In the Caltech experiments, the researchers stripped an HIV virus of its disease-causing elements and used it to virally infect single-cell embryos of mice with a gene from a jellyfish.

Any number of different genes could have been selected. For the purpose of the studies, the researchers chose a specific jellyfish gene that could serve as a "marker" to indicate whether the gene transfer was successful. The gene produces a protein that gives the jellyfish a green fluorescence.

When the mice were born, they carried the jellyfish gene in their own genes. Under fluorescent light, all their major tissues and organs—including skin, bones, muscles, lungs, liver, kidney, stomach, brain, and retina—emitted a green glow.

The trait became a permanent feature of the mice's genome and was passed along to many of their offspring.

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