TSRI Scientists Work to Revive Species in 'Frozen Zoo'

By Madeline McCurry-Schmidt

They don’t roar, chirp or growl—yet.

Members of the Frozen Zoo^®, a biobank run by the San Diego Zoo Institute for Conservation Research, belong to a collection of living animal cells held in suspended animation. In collaboration with Professor Jeanne Loring’s lab at The Scripps Research Institute (TSRI), researchers are working to use these cells to bring species back from the edge of extinction.

The cells live in culture plates and frozen vials. The hope is that these cells, which often come from small skin samples, might one day be reprogrammed into stem cells, which could then be used to rescue endangered or recently extinct species.

“It’ll take a true melding of all our expertise to get this to work,” said Marisa Korody, a professional scientific collaborator at TSRI and postdoctoral fellow at the San Diego Zoo.

TSRI and San Diego Zoo scientists still have a long road ahead, but their work has already led to a better understanding of how stem cells might save species and even advance human health.

During a recent campus visit, Marisa Korody (left) and Thomas Nguyen (center) show a group of students a vial of frozen stem cells. (Photo by Cindy Brauer.)

A Roadmap for Rhinos

Of the more than 1,000 species in the Frozen Zoo^®, the project’s poster child is the northern white rhino. With only three northern white rhinos left in the world, researchers are racing to save the species.

The species also presents a scientific challenge. Northern white rhino cells have proven difficult to manipulate in the laboratory, providing an opportunity for scientists to overcome important obstacles in handling cells.

“Everything that we learn from rhinos, we can use for other animals,” said Korody.

The collaboration began as a conversation nine years ago between Loring and Oliver Ryder, director of Genetics at the San Diego Zoo Institute for Conservation Research. The Loring lab is investigating safe, effective techniques for turning adult cells into induced pluripotent stem cells (iPSCs), which can then differentiate into any cell type. The goal for the rhino cells is develop them into the sperm and eggs needed to create a new fertilized egg.

Stem cell reprogramming to produce new individuals is a strategy that has worked before—in mice—but scientists are finding that techniques that work in mice don’t work for all species. Just as different animals need different diets, different animal cell culture lines require different nutrients and conditions. Researchers have found that bird cells like to be kept at a higher temperature than reptile cells, for example. Amphibian cells like it even colder.

Korody said efforts to culture rhino cells took a step forward when the researchers developed a nutrient source, or “medium,” that allowed rhino cells to thrive. In 2011, researchers from the Loring lab reported a way to turn the zoo’s rhino cells into iPSCs. In 2016, the journal Zoo Biology published a new roadmap for the project, developed by Loring, Ryder, and other collaborators from four continents.

Hope for All Species

The researchers hope to someday implant a northern white rhino embryo into a surrogate mother, a southern white rhino. This new rhino won’t be a clone, but a new individual. “No two sperm are the same, and no two eggs are the same,” explained Thomas Nguyen, a researcher in the Loring lab who is supported by the California Institute for Regenerative Medicine (CIRM).

The researchers have samples from 12 northern white rhinos to draw from. This will still leave a limited gene pool, but genetic sequencing has shown that the southern white rhino population bounced back after an even worse genetic bottleneck.

In addition to the moral imperative to save these animals—poaching and habitat destruction by humans is what killed them off—the scientists see this as a chance to advance biomedical research.

“Every little thing that we learn helps us understand more about ourselves,” said Nguyen.

In other projects, the lab’s stem cell reprogramming techniques are being applied to human diseases, including Parkinson’s disease and multiple sclerosis. iPSCs have also opened up new studies into autism and Fragile X syndrome, and the studies into rhino reproductive cycles have the potential to help people struggling with infertility.

Inspiring Future Conservation

The project has also given scientists an opportunity to share conservation biology and biomedical research with the public.

On a recent Tuesday afternoon, a group of elementary- and middle school-aged students from Heschel Day School in Los Angeles visited TSRI for a tour of the Loring lab.

The researchers have given themselves a timeline of 15 to 20 years to breed a northern white rhino using stem cell techniques. With that timeline, these students might be among the generation of scientists who brings the northern white rhino back.

The students and their teachers put on lab coats and posed for a group photo between two lab benches. Korody held up a vial of stem cells.

“Do the cells have a name?” one teacher asked.

“These are Angalifu,” said Korody. Angalifu was the second-to-last male northern white rhino alive in the world (“In the universe,” Nguyen noted). He died in 2014, but his cells live on.

The students grinned for their photo. “Say Angalifu!” said their teacher.

“Angalifu!” they yelled.

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