Cells at San Diego Zoo lead to cloning of endangered horse

Meet Kurt the cloned pony: Scientists at San Diego zoo use 40-year-old stallion cells to create endangered horse

  • Kurt is a two-month-old colt who is actually a clone of an Przewalski’s horse
  • He was created from cells taken from a stallion that had sat frozen for 40 years 
  • The small, stocky animals are believed to be extinct in the wild  

Little Kurt looks like any other baby horse as he frolics playfully in his pen. 

He is not afraid to kick or head-butt an intruder who gets in his way and, when he’s hungry, dashes over to his mother for milk.

 But there the similarities  end because Kurt is a clone.

 The 2-month-old colt is a Przewalski’s horse, a species native to central Asia that once went extinct in the wild and is still critically endangered, with only about 2,000 remaining.

San Diego Zoo Global researchers have high hopes that Kurt can help turn things around for his species. 

“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.


This Sept. 1, 2020 photo provided by San Diego Zoo Global shows Kurt, a tiny horse who is actually a clone

 Kurt was cloned from skin cells taken from a stallion in 1980 and safeguarded at the Frozen Zoo, San Diego Zoo Global’s vast repository of 10,000 cell lines from more than 1,100 species and subspecies.

  The rare, endangered Przewalski’s horse was created from cells taken from a stallion that had sat frozen at the San Diego Zoo for 40 years before they were fused with an egg from a domestic horse.

With the egg’s nucleus removed, ensuring Kurt would be basically all Przewalski’s horse, they were implanted in the mare who would become his mom on Aug. 6.

The result, officials say, was the world’s first cloned Przewalski’s horse.

Scientists have cloned nearly two dozen kinds of mammals, including dogs, cats, pigs, cows and polo ponies. 

In 2018, researchers in China created monkeys for the first time using the cloning techniques that produced Dolly the sheep.

Kurt looks like any other baby horse as he frolics playfully in his pen. But the 2-month-old, dun-colored colt was created by fusing cells taken from an endangered Przewalski’s horse at the San Diego Zoo in 1980

The zoo sees Kurt’s birth as a milestone in efforts to restore the population of the horse also known as the Asiatic Wild Horse or Mongolian Wild Horse. 

The small, stocky animals (they stand only about 4 to 5 feet tall at the withers) are believed to be extinct in the wild and number only about 2,000 in zoos and wildlife habitats. 

However, every single animal alive in the world today is descended from one of 12 which were captured from the wild between 1899 and 1902.

This means the species has a very narrow range of genetic diversity, putting them at huge risk of disease and mutations emerging as a result of interbreeding. 

To mitigate this, breeding with as many different animals as possible is highly desirable, even if it is a cloned specimen of an animal which died 22 years ago.   

‘This colt is expected to be one of the most genetically important individuals of his species,’ Bob Wiese, chief life sciences officer at San Diego Zoo Global, which operates the zoo, said in a statement. 

‘We are hopeful that he will bring back genetic variation important for the future of the Przewalski’s horse population.’

Although only two months old, Kurt’s birth was made possible in 1980 when cells were taken from a five-year-old stallion of his species and put in deep freeze at San Diego’s Frozen Zoo facility. 

This stallion died in 1998 and is Kurt’s father. However, both of the animals are genetically identical, which does not occur in traditional births.  

Cloning may have its roots in science fiction but is now a scientific reality, with animals regularly cloned from the genetic material of a donor. 

The process is now relatively simple, DNA is taken from the nucleus of an animal which scientists want to clone. 

A donor egg cell, often from a related species or an experienced mother in captivity, is harvested and has its own genetic material ripped out. 

This barren cell is then injected with the intact nucleus, containing all the necessary DNA for life, from the donor. 

This hybrid cell is then carefully implanted in the uterus of a surrogate, which will become the animal’s adoptive mother, where it grows like a normal pregnancy. 

Kurt was named for Kurt Benirschke, who played a key role in founding the Frozen Zoo with its extensive research program and cell cultures. 

‘A central tenet of the Frozen Zoo, when it was established by Dr Benirschke, was that it would be used for purposes not possible at the time,’ Dr Ryder added.

The zoo worked in collaboration with the California conservation group Revive & Restore and the Texas-based company ViaGen Equine in creating Kurt.

He was born at a veterinary facility in Texas where he’ll continue to live with his adopted mother for most likely another year.

Scientists inspecting cell cultures at San Diego Zoo Global’s Frozen Zoo, a collection of tissue and genetic material that has been collected by conservation researchers since it was founded in 1972.Cells at the San Diego Zoo have lead to the cloning of an endangered horse

Eventually he’ll be integrated into the zoo’s Przewalski’s horse population, where it’s hoped someday he’ll become a father himself.

Przewalski’s horses take their official name from Russian explorer Nikolai Przewalski, who found a skull and hide of one and shared it with a Russian museum.

At one time they ranged throughout Europe and Asia, according to the Smithsonian’s National Zoo and Biology Conservation Institute. 

Encroaching human population and livestock eventually pushed them out of Europe and east to parts of Asia like the Gobi Desert. 

Outside of zoos, they exist today only in reintroduction sites in Mongolia, China, and Kazakhstan.

According to the Smithsonian, they are the only true wild horses left in the world. 

The institute maintains wild horse herds in North America and Australia don’t count because they are the ancestors of escaped domesticated horses.


What is cloning?

Cloning describes several different processes that can be used to produce genetically identical copies of a plant or animal.

In its most basic form, cloning works by taking an organism’s DNA and copying it to another place.

There are three different types of artificial cloning: Gene cloning, reproductive cloning and therapeutic cloning.

Gene cloning creates copies of genes or parts of DNA. Reproductive cloning creates copies of whole animals.

Therapeutic cloning produces embryonic stem cells for tests aimed at creating tissues to replace injured or diseased tissues.

To create somatic cell nuclear transfer (SCNT) clones, scientists take DNA (red circle) from tissue and insert it into egg cells (yellow) with their DNA (green) removed. The scientists then switch on or off certain genes to help the cells replicate (right)

Dolly the Sheep was cloned in 1996 using a reproductive cloning process known as somatic cell nuclear transfer (SCNT).

This takes a somatic cell, such as a skin cell, and moves its DNA to an egg cell with its nucleus removed. 

Another more recent method of cloning uses Induced pluripotent stem cells (iPSC).

iPSCs are skin or blood cells that have been reprogrammed back into an embryonic-like state.

This allows scientists to design them into any type of cell needed.

Could we ever clone a human? 

Currently there is no scientific evidence that human embryos can be cloned.  

In 1998, South Korean scientists claimed to have successfully cloned a human embryo, but said the experiment was interrupted when the clone was just a group of four cells. 

In 2002, Clonaid, part of a religious group that believes humans were created by extraterrestrials, held a news conference to announce the birth of what it claimed to be the first cloned human, a girl named Eve.

This was widely dismissed as a publicity stunt.  

In 2004, a group led by Woo-Suk Hwang of Seoul National University in South Korea published a paper in the journal Science in which it claimed to have created a cloned human embryo in a test tube. 

Gene cloning creates copies of genes or parts of DNA. Reproductive cloning creates copies of whole animals (stock image)

In 2006 that paper was retracted. 

According to the National Human Genome Research Institute, from a technical perspective cloning humans is extremley difficult.

‘One reason is that two proteins essential to cell division, known as spindle proteins, are located very close to the chromosomes in primate eggs,’ it writes.

‘Consequently, removal of the egg’s nucleus to make room for the donor nucleus also removes the spindle proteins, interfering with cell division.’

The group explains that in other mammals, such as cats, rabbits and mice, the two spindle proteins are spread throughout the egg. 

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