Frozen Zoo Cells May Let Scientists Clone Endangered Beasts
(Correct spelling of scientist’s name in fourth paragraph of story published June 10.)
For a northern white rhinoceros, Angalifu has a pretty sweet life. The two-ton rhino can roam freely through a 213-acre habitat designed to mimic an African savannah. Still, Angalifu and Nola, an elderly female, are two of just eight northern white rhinos known to be left on earth.
“These beautiful animals are on the brink,” says Oliver Ryder, 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 at the institute where skin cells and DNA from 12 white rhinos and 8,400 other animals -- about 800 species in all -- are stored at -280 degrees Fahrenheit. The hope is that the cells can one day be used to create cloned animals and replenish endangered species. This winter, Scripps Research Institute scientists in La Jolla, California, 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, proving their viability, Bloomberg Businessweek reports in its June 14 issue.
“I thought, ‘We’ve done it!’” Jeanne Loring, who led the research, said in an interview. “It gives me hope we can help save species from extinction.” The next step, she said, will be to use the stem cells in some variation of the method used to clone Dolly the sheep.
In 1996, Scottish researchers made Dolly by transferring the nucleus of an adult sheep cell into a developing egg cell whose own nucleus had been removed. They used embryonic stem cells in that process. Loring would use the stem cells she developed from the drill’s skin, she said, since embryos from endangered animals are hard to come by.
Loring might also try mixing stem cells from the drill with a three- to four-day-old embryo from a similar animal that’s in plentiful supply, like a baboon, she said. Offspring from this mix could be selectively mated to breed out the non-drill genes, in theory leaving a pure drill.
While the Frozen Zoo was founded in 1972 -- long before “Jurassic Park” sent a back-from-the-dead Tyrannosaurus Rex snarling across movie screens -- the technology needed to make good use of the stored cells is just now being developed. Loring used a technique developed in 2007 by Shinya Yamanaka of Kyoto University in Japan that uses a harmless virus to carry genes into skin cells to change them into stem cells.
Scientists have harvested stem cells from embryos for more than a decade. 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, about half its normal life span, and died in April.
“There has been a lot of suffering with these early deaths and these malformations,” Fiester said in a telephone interview. While preserving endangered species might be a worthy goal, the benefit may be limited if only a handful of animals are created and they live in zoos, she said.
Ryder acknowledges the problems. “We would only engage in these efforts if there were no other way to prevent extinction of a species,” he says.
Loring’s team, led by postdoctoral scientist Inbar Friedrich Ben-Nun, now plan to map the rhino’s genome to gain clues about which genes to use to reprogram cells. In the meantime, they’re focused on the drill.
There are three ways stem cells might be used to create clones, Loring said, and none of them will be easy.
One way would be to mimic the process that created Dolly. Another would mix stem cells from the drill with the early embryo cell of a similar animal.
Eventually, she’d like to figure out how to turn stem cells into the most elusive and potent cells of all -- sperm and egg. If she could do this, Loring said, the cells could come together in a petri dish in an act of in-vitro fertilization.
Loring will present her work June 17 at the annual meeting of the International Society for Stem Cell Research in San Francisco.
In December, conservationists working to save the northern white rhino released four of them in a wildlife conservancy in Kenya in a last-ditch effort to encourage them to breed in the wild.
For Ryder, the only rationale for cloning is to create new animals that could mate with existing ones, boosting their population and genetic diversity. Even if cloning efforts don’t succeed, the creation of stem cells from endangered animals may lead to new therapies for conditions like diabetes, which many drill suffer from -- the same payoffs researchers hope for in humans.
Loring and Ryder are racing against time. Angalifu is about 40, and northern white rhinos generally don’t live past 50.