Scientists have cloned the first member of the equine family: a mule, a cross between a mare and a donkey. The mule is also the first sterile and first hybrid animal to be cloned. Researchers at the University of Idaho and Utah State University did the work.
The first equid joins the ranks of the cloned, which includes cows, sheep, cats, rabbits, rodents, and swine.
Coming around the track
At press time, two healthy mules had been born and researchers were expecting the birth of one more mule, according to Dr. Dirk Vanderwall, assistant professor in the Department of Animal and Veterinary Science at the University of Idaho-Moscow.
The first cloned mule, Idaho Gem, was born in May and was the subject of an article published online in Science on May 29. The second mule, Utah Pioneer, was born in June.
Both cloned foals are full siblings of the racing mule Taz, owned by Donald Jacklin. An Idaho businessman and mule enthusiast, Jacklin provided the primary funding for the project, believing it had a lot to offer the mule industry, especially mule racing.
"He (Jacklin) saw cloning as a technology that would have real applications with mules, since they are a sterile hybrid," Dr. Vanderwall said. The project also received support from the Idaho Equine Education Bill, through which tax money from the racing industry is set aside for research.
Currently, the American Mule Racing Association allows cloned mules to compete in all races, including the Olympics. And while the cloning success may be encouraging for those trying to clone horses, including Texas A&M researchers, it means little for horse racing.
Several horse regulatory bodies, including the Jockey Club and the American Quarter Horse Association, have made regulations in recent years that prohibit the registration and racing of clones. "The Jockey Club is an organization that believes that the short-term and long-term welfare of the Thoroughbred breed is better served without the use of these prohibited practices, including cloning," explained Bob Curran Jr., vice president of corporate communications for The Jockey Club.
The mule cloning success is long in coming. Researchers have been working toward the goal since 1998 but have had difficulties because equine oocytes don't mature well in a dish, and embryonic cells don't divide easily. When the group found that calcium concentrations in equine red blood cells are low, compared with those from humans, they suspected that low calcium concentrations could be key in inhibiting embryo growth. After increasing the calcium concentrations in the cultures and several more tries, they finally succeeded.
The foals carry identical DNA from a fetal cell culture established five years ago at the UI-Moscow, using Taz's mother and father. The team took somatic cells from the fetus, fused them with an enucleated horse oocyte, and then inserted this into a mare.
While Donald Jacklin may have funded the research to benefit the mule industry, the project may also have an additional benefit. Dr. Gordon Woods, lead researcher on the project at UI-Moscow, says the mule clone may help shed some light on human cancers. "There are electrifying similarities between cancer metastasizing and embryo division," Dr. Woods said. "The contrasts and similarities between humans and horses at the cellular level provide a number of insights about how the relationship of certain chemicals in the body affect both normal and abnormal cell activity."
For example, he explained, the mortality rate for horses with metastatic cancer is 8 percent for all cancers and 0 percent for prostate cancer. By comparison, the mortality rate in humans is approximately 24 percent for all cancers, of which 13 to 14 percent are for prostate cancer. Dr. Woods thinks calcium concentrations may play a role in these differences.
"We are thrilled," said Leah Patton, an executive of the American Donkey and Mule Society, an organization that formally registers mules and donkeys. "We are glad that the first equine was a mule and we hope that cloning a mule can help further medical research and other research."