Scientists at San Diego Zoo clone endangered Przewalski’s horse

Kurt looks and acts like any other young horse. He scurries and strides on springy legs and tests their strength. When it’s time to recharge, he snuggles up to his mother for some nutritious milk.

But Kurt is no ordinary colt. Kurt is a clone.

The 2 month old is a Przewalski horse, a species native to Central Asia that has become extinct in the wild and is still critically endangered. Only about 2,000 are left.

Researchers at San Diego Zoo Global, the nonprofit that runs the San Diego Zoo, sincerely hope that Kurt can help change things for his species. It was cloned from the skin cells of a stallion in 1980 and protected in the Frozen Zoo, the organization’s repository with 10,000 cell lines from more than 1,100 species and subspecies.

“By ‘bringing cells to life’, if you will, making an animal out of a cell, we can bring back a portion of the gene pool that would otherwise be lost,” said Oliver Ryder, director of genetics at San Diego Zoo Global.

It is the first time anyone has successfully cloned a Przewalski horse. This is only the third species that San Diego Zoo Global has ever cloned – along with Gaur and Banteng, two endangered species of cattle that were cloned in the early 2000s.

Kurt, the very first Przewalski horse clone.

(Scott Stine)

Gallop poll

Each living Przewalski horse is related to 12 wild ancestors. This limited gene pool is not a good sign for the species as genetic diversity is required to adapt to habitat changes and ward off new diseases.

So the researchers were excited to find a stallion with bits of DNA that the rest of his species largely lacked.

Think of it this way: each of your parents passed half of their genetic material on to you, which means you didn’t get half from each. If you have a sibling, that person likely has at least part of the missing half. And the more siblings you have, the more DNA your parents have passed on to future generations.

This stallion’s ancestors hadn’t reproduced as well as other Przewalski’s horses, so he had rare pieces of DNA that would be lost forever if not passed down in some way.

That realization started a partnership between the San Diego Zoo, the Bay Area Conservation Group Revive & Restore, and ViaGen Equine, a Texas-based company that has experience in horse cloning.

For 40 years, the stallion’s cells sat frozen at minus 320 degrees Fahrenheit – colder than an evening on Mercury. The researchers revived the cells and fused one with an unfertilized egg from a domestic horse. Since scientists had removed the nucleus of the egg, the part that contained its DNA, almost all of the genetic material came from the stallion.

The team then planted the egg back in the horse that served as the surrogate mother. It is the same method known to have been used to clone Dolly sheep in 1996 and has since been used to clone cattle, cats, deer and horses, among others.

Dr.  Barbara Durrant uses forceps to pick up vials of frozen sperm, eggs, ovarian and testicular tissue of various types.

Dr. Barbara Durrant of the San Diego Zoo Global uses tongs to pick up vials of frozen sperm, eggs, and ovarian and testicular tissue from various bird, mammal and reptile species.

(Hayne Palmour IV / San Diego Union-Tribune)

Horse game

Kurt was born on August 6th at a Texas veterinary center owned by a partner of ViaGen Equine. He’s still there. It was named after the late Dr. Kurt Benirschke, a UC San Diego geneticist who was instrumental in creating the Frozen Zoo.

It is planned to eventually take Kurt to the San Diego Zoo Safari Park, where he will join the park’s 14 Przewalski horses as part of a conservation and breeding program.

However, according to Ryder, the facility won’t be phasing him out anytime soon. That’s because Kurt needs at least another year with his surrogate mother. At this point he has to learn how to handle other young horses. Only then will it be taken to Safari Park, where researchers hope it will produce healthy offspring who may one day be returned to the wild.

These kinds of efforts will take generations, says Megan Owen, director of conservation science at San Diego Zoo Global, but are vital.

“The genetic diversity associated with these breeding programs is critical for these small populations in the wild,” she said.

Wosen writes for the San Diego Union-Tribune.

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