August 7, 2003

A new entry has slipped into the equine cloning derby. Prometea, a Haflinger foal, was born to her genetically identical mother on May 28, 2003, in Cremona, Italy.

The first cloned equine, a mule named Idaho Gem, was born May 4, 2003. Two other mule clones have been born since the birth of Prometea, one in June and the other in July of this year, but Prometea is the first cloned horse.

Prometea, the first cloned horse, with her genetically identical surrogate mother. Courtesy C. Galli

“She’s growing up very well, without any problems,” says Cesare Galli of the Laboratory of Reproductive Technologies in Cremona, who led the cloning effort. “She is both the first horse to be cloned and the first clone to be carried by her twin mother.”

Prometea was cloned from the skin cells of the same horse that carried her pregnancy, making surrogate mother and foal genetic doubles. The mules, in contrast, were derived from the DNA of a mule fetus, and the resulting embryos were implanted into a horse.

The approach used to clone Prometea is unusual, because some researchers thought it was impossible for a mother to give birth to her identical twin. During normal pregnancies, the maternal immune system recognizes the fetus as foreign and produces certain immune proteins. These proteins are thought to sustain the pregnancy.

“This came as a surprise to many people,” says Galli. “It had been demonstrated that the fetus thrives on the maternal immune response. But that is clearly not at work here.”

To create Prometea, the researchers cultured skin cells from a Haflinger mare and fused them with oocytes that had no nucleus. Out of more than 300 embryos created, only 14 were viable after being in culture for seven days.

Two of these embryos were implanted into the same mare from which the cell line was derived. The remaining embryos were implanted into other surrogate mares. The only embryo that survived to term was Prometea.

After the success of the thoroughbred gelding Funny Cide in the Kentucky Derby and the Preakness this spring, horse racing fans greeted the prospect of equine clones with enthusiasm as a way of reproducing geldings, which are sterile. However The Jockey Club, which oversees the breeding and registration of all thoroughbreds, “expressly prohibits” the cloning of thoroughbred race horses, according to Bob Curran, vice president of corporate communications.

“I would never say ‘never,’ but at present, we are doing what we believe is best for the health and welfare of the breed,” says Curran. “We believe natural breeding is better than any artificial reproductive technologies.” However, Curran says that if in the future it appeared that cloning would improve the short- or long-term interests of the breed, the issue might be reconsidered.

Galileo, the frist cloned bull, depicted here as a prisoner of the Italian government. Courtesy C. Galli (modified by M.S. Gibbs) Clones Who Challenge Authority Cesare Galli says the cloned foal was called Prometea as a sort of continuing joke of naming clones after figures who defy authority. The foal was named for Prometeo, a Titan in Greek mythology who rebelled against Zeus and stole fire from Mt. Olympus. "She is like the Greek Titan, because she challenged the establishment and the current thinking," says Galli. When the researchers cloned the first bull, they named him Galileo because they were expecting opposition from the Italian health minister, a fervent Catholic. The health minister claimed that the researchers had violated a 1998 decree forbidding cloning and brought the researchers to court. Galileo and his father, a famous bull named Zoldo, were confiscated, a fate similar to that of Galileo Galilei, the 17th-century astronomer who was imprisoned for his heresy. Much to the chagrin of the health minister, Galli and his colleagues eventually won their case, because Galileo had been cloned before the new law was imposed.

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Galli, C., et al. A cloned horse born to its dam twin. Nature 424, 635 (Aug. 7, 2003).

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