Many of the steps of cloning and subsequent embryonic development are done in test tubes in incubators. These conditions are not perfect substitutes for the female reproductive tract where fertilization and early embryonic development normally occur.
Sometimes abnormal fetuses develop to term , resulting in abnormalities at birth. The problems stem from an abnormal placenta. At birth, these clones are genetically normal, but are overly large, and tend to be hyperinsulinemic and hypoglycemic.
The conditions normalize over time once the offspring is no longer influenced by the abnormal placenta. Recent improvements in cloning procedures have greatly reduced these abnormalities, which also occur with natural reproduction, but at a much lower incidence. Many thousands of cloned mammals have been produced in nearly two dozen species.
But the cloning research landscape is changing fast. The driving force for producing Dolly was not to produce genetically identical animals. Rather researchers want to combine cloning techniques with other methods in order to efficiently change animals genetically — much quicker than traditional animal breeding methods that take decades to make changes in populations of species such as cattle.
One recent example is introducing the polled no horns gene into dairy cattle , thus eliminating the need for the painful process of dehorning. An even more striking application has been to produce a strain of pigs that is incapable of being infected by the very contagious and debilitating PRRS virus.
Researchers have even made cattle that cannot develop Mad Cow Disease. For each of these procedures, somatic cell nuclear transplantation is an essential part of the process.
To date, the most valuable contribution of these somatic cell nuclear transplantation experiments has been the scientific information and insights gained. But it was Dolly who had captured our imagination. Was it because she was a warm-blooded animal, a mammal, much closer to human? If you could do it in a sheep, you could do it on us!
It was amazing to see a differentiated cell — an adult cell specialized to do its particular job — transform into an embryonic one that could go on to give rise to all the other cells of a normal body. We researchers wondered if we could go further: Could we in the lab make an adult cell once again undifferentiated, without needing to make a cloned embryo?
He went on to be the Nobel corecipient with Gurdon for showing that mature cells could be reprogrammed to become pluripotent : able to develop into any specialized adult cell. Now we have the possibility of making individualized replacement cells — potentially any kind — to replace tissue damaged due to injury, genetic disorders and degeneration.
Not only cells; we may soon be able to have our own organs grown in a nonhuman host , ready to be transplanted when needed. If Dolly was responsible for unleashing the events that culminate with new methods of making fully compatible cells and organs, then her legacy would be to improve the health of practically all human beings on this planet.
And yet, I am convinced that there are even better things to come. In the winter of , I found myself driving on the wrong side of the road through the Nottingham countryside. Keith was a smart, fun, loving friend who, along with Ian Wilmut and colleagues at the Roslin Institute , had brought us Dolly 15 years earlier.
Dolly the sheep was the first animal to be cloned from an adult cell, and like many firsts, she came to stand in for all of her kind. So when scientists suspected she had short telomeres —stretches of DNA that normally shorten with age—people wondered if it was because she was cloned from an adult cell. A certain narrative took hold. They were quite healthy for their age.
So of course, he kept getting questions, like if these animals are so healthy, then why was Dolly so unhealthy? It was Dolly that everyone cared about. Sinclair would point out that Dolly was not so unhealthy. Dolly had six lambs with a Welsh Mountain sheep named David.
Their first lamb, Bonny, was born in the spring of Twins, Sally and Rosie, followed the next year and triplets, called Lucy, Darcy and Cotton, the year after that. Dolly having an ultrasound scan during one of her pregnancies. Dolly the Sheep with her first born lamb, called Bonnie. Dolly the sheep in a field. In the autumn of , Dolly was seen to be walking stiffly. X-rays confirmed that Dolly had arthritis. It fuelled the suspicion that cloned animals were destined to age prematurely.
The cause of the arthritis was never established but daily anti-inflammatory treatment resolved the clinical signs within a few months. Although her arthritis was a concern for the animal carers at Roslin, a much more serious problem was feared. In January , a cloned sheep called Cedric died. The post mortem revealed that Cedric had died of sheep pulmonary adenomatosis SPA.
0コメント