Researchers Show Clone from Aged Cow
Can Produce Normal Calf
UConn researchers announced last week that a Holstein heifer named "Daisy", cloned two years ago from an aged cow, has given normal birth to a 90-pound male calf.
The calf, named "Norm", was born at the Kellog Dairy Center on June 3, says Xiangzhong (Jerry) Yang, professor and head of the Transgenic Animal Facility.
What makes Norm's birth special, Yang and his colleagues say, is that Daisy was cloned from an aged animal (past menopause). The fact that Daisy can reproduce normally demonstrates that the cloning process can reverse the physiological aging process.
Yang suggests that Norm's successful birth moves science a bit closer to the promise of "therapeutic cloning," in which human cells would be harvested for tissues that could treat diseases such as diabetes or Parkinson's.
Scientists have previously reported on cloned cows giving normal births in Japan, but those clones were made from young donor cows or from slaughterhouse animals of unknown age.
Ever since researchers in Scotland electrified the world by cloning "Dolly" the sheep, scientists were concerned that cloned animals might age prematurely, reflecting the age of the DNA of the animals from which they were cloned.
Recently, Yang's team reported in the journal Nature Genetics that all clones have normal cells with regard to telomeres (lengths of DNA on the ends of chromosomes), and are indistinguishable from calves produced through conventional reproduction. Their results showed that calves cloned from aged cows do not inherit the cellular genetic age of their donor and do not have cells that are unnaturally old.
"The normal birth of 'Norm' provides evidence that when you clone from an aged individual, you do not get an aged copy," Yang says.
Despite other reported problems associated with cloning, including high rates of abortion and neonatal death, Yang says research has shown that cloned animals, once they have passed the first few critical days after birth, can live and reproduce like conventional ly reproduced animals. Yang notes that his UConn research team and their Japanese collaborators have produced several dozen clones from adult cattle, male and female. Almost all the surviving clones appear normal.
"These findings are significant because of their important medical implications," adds Yang.
"Therapeutic cloning is aimed to convert skin cells or other somatic (body) cells from diseased individuals to embryonic stem cells, which may then be differentiated into any needed cell or tissue types for therapy," he says.
Yang says Norm's birth is also significant for agriculture and saving endangered species. It is desirable to be able to clone animals that have been proven valuable, and desirable for those clones to be able to reproduce normally, he adds.
Daisy was cloned from a 13-year-old high-merit cow named "Aspen," and was born at UConn on July 7, 1999.
Daisy is the fourth live clone produced at UConn. Her older sister "Amy", born on June10, 1999, was the first clone of an adult large animal in North America. A total of 10 clones have been produced from Aspen, including four - Amy, Betty, Cathy and Daisy - that are still alive.
Aspen, who also is still living, is now nearly 15 years of age and has long passed her calf-bearing age. She had a particularly high milking record, producing approximately 35,000 pounds of milk per year. It is yet to be determined whether her clones will have the same high milk production ability.