A bull cloned from the clone of a prize-winning animal four years ago is healthy and fertile, Japanese researchers announced last week. The second generation clone was created using a skin cell, taken from a first generation clone when the animal was only four months old. The research, published in the journal Nature Biotechnology, means that cows join mice as the only two species for which 'serial cloning' has so far proved successful.
Researchers at the Kagoshima Prefectural Cattle Breeding Development Institute in Japan used SCNT (somatic cell nuclear transfer), the technique used to create Dolly the sheep, to clone a bull famous for siring more than 350,000 calves. They created six clones of the animal in 2000, and managed to create a clone of one of those calves, following hundreds of experiments. The team used 665 eggs to produce 358 cloned cow embryos, of which 19 were transferred into cows. Two cloned calves were born alive, but one died shortly after birth.
Both the first and second generation clones appear healthy, say the researchers: 'We have proven that recloning can be done in higher species'. Team leader Jerry Yang says the most exciting part is that the second generation clone is quite fertile, while the first generation clones have limited fertility, although he has no idea why. Despite attempts using 248 eggs, the scientists have not yet managed to create a third generation clone.
The original animal, a black bull named Kamitakafuku, was cloned because he was getting old, and researchers wanted to preserve his ability to produce offspring with high quality meat. He died, aged 21, in 2001. The ability to create second generation clones would speed the normal breeding process, since animals can be cloned when they are just a few months old.
Interestingly, the scientists found that the cells of the second generation clones showed no signs of premature aging, in the form of shortened telomeres ('caps' on the ends of a cell's chromosomes, which shorten every time a cell divides into two new cells). When its telomeres drop below a critical length, a cell stops producing new cells, and dies. Research on Dolly the sheep suggested that cloned animals might age faster than normal animals, since they are created using the genetic material of cells that have already divided many times. But the cloned bulls, like the six generations of serially cloned mice reported in 2000, appear to have normal length telomeres.
Sources and References
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Researchers Clone Calf From Cloned Bull
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Bullish hopes for serial cloning
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Researchers clone calf from cloned bull
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