With only two female northern white rhinoceros left on Earth, conventional breeding techniques to bring them back from the brink of extinction are no longer an option. Scientists, now turning to advanced reproductive technology to save the species, have completed a key step: mapping the creature’s entire genome, they report in the journal Proceedings of the National Academy of Sciences.
With that information in hand, scientists can now use it to evaluate the health of previously developed stem cells. Stem cells can be biologically coached into becoming many other cell types — an ability scientists refer to as pluripotency. The hope is to goad the preserved pluripotent stem cells into both sperm and egg, fertilize the egg in vitro, then implant it into a surrogate mother. If successful, this approach could be applied to other endangered species.
“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,” Jeanne Loring, an emeritus professor at the Scripps Research Institute in San Diego and an author of the paper, said in a press release. “This is great progress not only for white rhinos, but for the entire field of animal conservation.”
Preventing White Rhino Extinction
Having a “reference genome” in hand is essential for quality control in a project that has little room for error; the researchers have a finite number of white rhino stem cells. The genetic blueprint now allows scientists to screen stem cells for mutations they may have picked up during growth in the label. Researchers have seen harmful mutations emerge before in both human and animal lab-grown stem cells.
They have already found one such problematic cell line by comparing the reference gene to that of the lab-created cell line. In doing so, the researchers learned that one of the most promising stem cell lines was missing more than 30 million base pairs affecting over 200 genes — including some involved in reproduction. They can now provide the same type of analysis to the other eight cell lines they’ve created
“If we hadn’t built this genome, we wouldn’t have known that,” Loring said in the release. “We thought we had a good stem cell line, but it turns out it had a mutation that could have made it unsafe to use for reproduction. Now we can go back and screen all the others. This becomes the gold standard for deciding which cells to move forward with.”
The scientists also compared northern and southern white rhino genomes. Earlier data suggested that DNA differences between the two might make it risky to implant northern white rhino embryos into southern white rhinos. Now that they know that the two species genomes are quite similar, the scientists are more confident about their approach.
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Preservation Instead of De-Extinction
Unlike some de-extinction approaches, the strategy to preserve the northern white rhinos involves using existing DNA from a still-living subject, rather than trying to genetically engineer a close living relative using genetic information from an extinct one.
“That means we’re not trying to recreate a species from scraps of ancient, damaged DNA,” Loring said in the release. “We have the real thing.”
If this approach works in the northern white rhino, it could be applied to hundreds of species who already have had their stem cell seeds frozen and placed in a biobank.
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Article Sources
Our writers at Discovermagazine.com use peer-reviewed studies and high-quality sources for our articles, and our editors review for scientific accuracy and editorial standards. Review the sources used below for this article:
Proceedings of the National Academy of Sciences. Genomic map of the functionally extinct northern white rhinoceros (Ceratotherium simum cottoni)
Before joining Discover Magazine, Paul Smaglik spent over 20 years as a science journalist, specializing in U.S. life science policy and global scientific career issues. He began his career in newspapers, but switched to scientific magazines. His work has appeared in publications including Science News, Science, Nature, and Scientific American.
