The odds aren’t great for male northern white rhinos looking for love. Only two females are left on the planet, and imminent extinction does not seem to make rhinos particularly horny: the last time this captive population produced a baby was in 2000. Now, there may be a way to save this and other endangered species – with stem cells rather than sex.
For the first time researchers have turned frozen skin cells from two highly endangered species – the northern white rhino and the baboon-like drill – into stem cells that can become any cell in the body, including sperm and eggs. These could be used to impregnate animals through techniques similar to in vitro fertilisation (IVF).
Stem cells have already been created from ordinary cells in people, rhesus monkeys and mice. Jeanne Loring of the Scripps Research Institute in La Jolla, California, and her team has now done the same for a rhino and the drill (Mandrillus leucophaeus), a primate closely related to the mandrill, using frozen samples.
Loring’s work is made possible by a menagerie on ice called The Frozen Zoo, a collection of skin cells from more than 8600 animals representing around 800 species at the San Diego Zoo Institute for Conservation Research, California.
The two species chosen are among the most endangered animals in the world. Bushmeat hunting and habitat destruction threaten the drill, which is found only in Nigeria, south-western Cameroon and Equatorial Guinea: between 3000 and 8000 remain in the wild. The northern white rhino (Ceratotherium simum cottoni) is on the brink of extinction: 2230 individuals were alive in 1960 but only seven remain today – five males and two females, all in captivity.
Using viruses, the researchers introduced four genes that are highly expressed in human embryonic stem cells into the skin cells. This reverted the animals’ skin cells to their embryonic state. A few weeks later the researchers had colonies of induced pluripotent stem cells (iPSCs) for both drills and rhinos.
The researchers now hope to turn the drill iPSCs into sperm cells and the rhino iPSCs into egg cells, which could help preserve the species through techniques similar to IVF. They wouldn’t need a living drill or northern white rhino to carry the pregnancy – another primate could be a surrogate mother for a drill embryo, for instance.
But turning iPSCs into gametes will be difficult. Researchers have had some success in coaxing stem cells from mice and people to become primordial germ cells – the progenitors of sperm and eggs – but producing normal germ cells is hit and miss.
“It’s a huge next step to get from iPSCs to functional gametes,” says Debra Mathews of Johns Hopkins University in Baltimore, Maryland.
Nevertheless, says Loring, “what we’ve done is create a resource and sparked an idea. People in the conservation world would never have thought of this on their own.”
Journal reference: Nature Methods, DOI: 10.1038/nmeth.1706