Woolly mammoths’ closest living relatives are Asian elephants, which could be genetically engineered to have mammoth-like traits.Credit: Mark Garlick/Science Photo Library via Alamy
Scientists have finally managed to put elephant skin cells into an embryonic state.
The breakthrough — announced today by the de-extinction company Colossal Biosciences in Dallas, Texas — is an early technical success in Colossal’s high-profile effort to engineer elephants with woolly mammoth traits.
Eighteen years ago, researchers showed that mouse skin cells could be reprogrammed to act like embryonic cells1. These induced pluripotent stem (iPS) cells can differentiate into any of an animal’s cell types. They are key to Colossal’s plans to create herds of Asian elephants (Elephus maximus) — the closest living relative of extinct woolly mammoths (Mammuthus primigenius) — that have been genetically edited to have shaggy hair, extra fat and other mammoth traits.
“I think we’re certainly in the running for the world-record hardest iPS-cell establishment,” says Colossal co-founder George Church, a geneticist at Harvard Medical School in Boston, Massachusetts, and a co-author of a preprint describing the work, which will soon appear on the server bioRxiv.
But the difficulty of establishing elephant iPS cells — in theory, one of the most straightforward steps in Colossal’s scheme — underscores the huge technical hurdles the team faces.
Endangered species
In 2011, Jeanne Loring, a stem-cell biologist at the Scripps Research Institute in La Jolla, California, and her colleagues created iPS cells from a northern white rhinoceros (Ceratotherium simum cottoni) and a monkey called a drill (Mandrillus leucophaeus), the first such cells from endangered animals2. Embryonic-like stem cells have since been made from a menagerie of threatened species, including snow leopards (Panthera uncia)3, Sumatran orangutans (Pongo abelii)4 and Japanese ptarmigans (Lagopus muta japonica)5. However, numerous teams have failed in their attempts to establish elephant iPS cells. “The elephant has been challenging,” says Loring.
A team led by Eriona Hysolli, Colossal’s head of biological sciences, initially ran into the same problems trying to reprogram cells from an Asian elephant calf by following the recipe used to make most other iPS cell lines: instructing the cells to overproduce four key reprogramming factors identified by Shinya Yamanaka, a stem-cell scientist at Kyoto University in Japan, in 20061.
When this failed, Hysolli and her colleagues treated elephant cells with a chemical cocktail that others had used to reprogram human and mice cells. In most cases, the treatment caused the elephant cells to die, stop dividing or simply do nothing. But in some experiments, the cells took on a rounded shape similar to that of stem cells. Hysolli’s team added the four ‘Yamanaka’ factors to these cells, then took another step that turned out to be key to success: dialling down the expression of an anti-cancer gene called TP53.
The researchers created four iPS-cell lines from an elephant. The cells looked and behaved like iPS cells from other organisms: they could form cells that make up the three ‘germ layers’ that comprise all a vertebrate’s tissues.
“We’ve been really waiting for these things desperately,” says Church.
Technological leaps
Colossal’s plan to create its first gene-edited Asian elephants involves cloning technology that does not require iPS cells. But Church says the new cell lines will be useful for identifying and studying the genetic changes needed to imbue Asian elephants with mammoth traits. “We’d like to pre-test them before we put them in baby elephants,” Church says. Elephant iPS cells could be edited and then transformed into relevant tissue, such as hair or blood.
But scaling up the process would require numerous other leaps in reproductive biology. One path involves transforming gene-edited iPS cells into sperm and egg cells to make embryos, which has been accomplished in mice6. It might also be possible to convert iPS cells directly into viable ‘synthetic’ embryos.
To avoid the need for herds of Asian elephant surrogates to carry such embryos to term, Church imagines that artificial wombs, derived in part from iPS cells, would be used. “We do not want to interfere with the natural reproduction of endangered species, so we’re trying to scale up in vitro gestation,” he says
Time and effort
Loring, who last year co-organized a conference on iPS cells from endangered animals, says adding elephants to the list is important, but not game-changing. “It will be useful for others who are having challenges reprogramming the species they’re interested in,” she says.
Sebastian Diecke, a stem-cell biologist at the Max Delbrück Center for Molecular Medicine in the Helmholtz Association in Berlin, would like to see more evidence that iPS cell lines grow stably and can be transformed into different kinds of tissues, for instance, by making brain organoids with them. “There are still steps before we can call them proper iPS cells,” he says.
Vincent Lynch, an evolutionary geneticist at the University at Buffalo in New York, has been trying — and failing — to make elephant iPS cells for years. He plans to attempt the method Hysolli and her colleagues developed, as part of his lab’s ongoing efforts to understand why elephants seem to develop cancer only rarely.
The myriad technologies needed to grow an iPS cell into a mammoth-like elephant might not be even close to ready yet. But given enough time and money, it should be possible, Lynch says. “I just don’t know the time frame and whether it’s worth the resources.”