There are two female northern white rhinos left in the world, and that is it. With no more males, this subspecies is on the very brink of extinction. But a long-dead rhino’s cells might allow scientists to bring these animals back from the edge.
Over a decade ago, skin cells were taken from Angalifu, a male northern white rhinoceros. These cells were then cryopreserved by San Diego Zoo's Frozen Zoo, with the hope that they might prove useful to future conservation efforts.
Using the latest genomic methods, an international team of scientists at Scripps Research, the San Diego Zoo Wildlife Alliance, Max Planck Institute for Molecular Genetics, and other collaborators have created an incredibly detailed northern white rhino genome.
From this genome, researchers have gleaned important pieces of information that may help save the subspecies, with the insights being published in PNAS.
Gene mapping the northern white rhino
First of all, the genome shows that the northern white rhino is not hugely different from the much more numerous southern white rhino. This means that a northern white rhino embryo could probably be carried to term by a southern white rhino surrogate.
"What's so exciting about this milestone is that we're getting closer to being able to rescue animals that otherwise might go extinct during our lifetimes," says co-senior author Jeanne Loring, professor emeritus at Scripps Research and a research fellow at the San Diego Zoo Wildlife Alliance. "This is great progress not only for white rhinos, but for the entire field of animal conservation."
This has only been possible as the Frozen Zoo froze cells actually belonging to the northern white rhino – known as biobanking.
"That means we're not trying to recreate a species from scraps of ancient, damaged DNA. We have the real thing," says Loring.
New hope for northern white rhinos
Ultimately, the goal is to grow healthy embryos and implant them into surrogate mothers, then raise the resulting calves in protected environments. It's not Jurassic Park, Loring is quick to point out, and it doesn't depend on gene editing or engineering.
"We're not resurrecting a mystery species – we're restoring one we still know intimately," she adds. "The rhino is big, gentle and unforgettable. It's the perfect symbol for what science can do to fight extinction."
But with no males of the northern white rhino subspecies left, where would this embryo come from?
Scientists have been growing northern white rhino stem cells in the lab. Stem cells are special cells because they are ‘undifferentiated’, which means they can turn into any kind of cell. The researchers hope to turn these stem cells into eggs and sperm, which can then be used to create a northern white rhino embryo.
But stem cell DNA is prone to picking up mutations in the lab. The new genome allows scientists to see what healthy rhino DNA should look like, and by comparing the stem cell DNA to the genome, they can therefore see which stem cells carry harmful mutations and which do not. By choosing the healthiest stem cells to create sperm and eggs, the scientists have the best chance of creating a viable embryo.
Find out more about the study: Genomic map of the functionally extinct northern white rhinoceros (Ceratotherium simum cottoni)
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Main image: one of the last female northern white rhinos, Fatu, grazes at the Ol Pejeta Conservancy in Nanyuki.
