San Diego's Frozen Zoo stores cells of endangered species such as the white rhino, but it's a controversial procedure that hasn't yielded optimal results
For a northern white rhinoceros, Angalifu has a pretty sweet life. The two-ton rhino can roam freely through a 213-acre habitat that resembles the African savannah. Still, Angalifu and his pal Nola, an elderly female at the zoo, are two of eight northern white rhinos believed to be left on the planet. "These beautiful animals are on the brink," says Oliver Ryder, the chief geneticist at the San Diego Zoo's Institute for Conservation Research. "There are a few left, but it's not clear they're capable of reproducing."
Ryder oversees the Frozen Zoo, a lab where skin cells and DNA from 12 white rhinos and 8,400 other animals—a total of some 800 species—are stored at -280F. The hope is that scientists can use the cells to create cloned animals and replenish endangered species.
The lab was founded in 1972, but technology needed to make use of the cells is just now being developed. This winter researchers at the Scripps Research Institute used tissue from the Frozen Zoo to create stem cells from the silver-maned drill, Africa's most endangered monkey. On June 1 the stem cells morphed into brain cells. "I thought, 'We've done it!' " says Jeanne Loring, who led the research. "It gives me hope we can help save species from extinction."
The next step will be to use the stem cells in some variation of the method used to clone Dolly the sheep. In 1996, Scottish scientists made Dolly by transferring the nucleus from an adult sheep cell into a developing egg cell that had its nucleus removed. They used embryonic stem cells in that process; Loring would use the stem cells she developed from the drill's skin since embryos from endangered animals are hard to come by. Loring and her team may also try mixing the drill cells with a three- to four-day-old embryo for a similar animal that's in plentiful supply, like a baboon. Offspring from this mix could be selectively mated to breed out the nondrill genes, in theory leaving a pure drill.
The cell-transformation technique, developed three years ago by Shinya Yamanaka of Japan's Kyoto University, uses a harmless virus to carry genes into skin cells—and change them into stem cells. Although the technique worked for the drill, it fell short when used with white rhino cells, so Loring is hoping to map the rhino's genome to get clues about which of its genes may reprogram cells.
Scientists have harvested stem cells from embryos for more than a decade, but Yamanaka's technology is important because embryos aren't always available for endangered species. Attempts to clone endangered animals, though, have led to aborted pregnancies and deformed offspring. In 2000, cells from the Frozen Zoo were used to clone two endangered types of cattle—a gaur and a banteng—using the Dolly method. Two of the three calves died shortly after birth. The surviving banteng lived at the San Diego Zoo for seven years, less than half its normal life span, and died in April.
Some scientists say those examples show the moral complexity of cloning. The benefit may be limited if only a handful of animals are created and live in zoos, says Autumn M. Fiester, a senior fellow at the Center for Bioethics at the University of Pennsylvania. "There has been a lot of suffering with these early deaths and malformations," Fiester says.
Ryder acknowledges the problems. "We would only engage in these efforts if there were no other way to prevent extinction," he says. For Ryder, the only rationale for cloning is to create new animals that could mate with existing ones, boosting their population and genetic diversity. With the white rhino, though, he and Loring are up against a deadline: Angalifu is pushing 40, and rhinos generally don't live past 50.
The bottom line: Clones made from skin cells may help revive endangered species, but some experts say cloning is the wrong solution to the problem.