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An animal with young cells is created through a cloning process

Cloning six cows from an old cell led to a breakthrough

by Tamara Traubman

Scientists will announce today that they have genetically replicated six cows whose body cells are younger than their chronological age. "Persephone, one of the cows, is about to celebrate her first birthday, and her cells look like the cells of a soft cart," Dr. Robert Lanza, of the biotechnology company, told Haaretz. "Advanced Cell Technology

One of the main reasons for carrying out research in cloning is the intention to use cloned animals to create a pool of organs to be transplanted into sick humans. However, it was quickly discovered that the first animal cloned from a mature cell, the sheep "Dolly", probably also "inherited" the age of her genetic mother, and her cells age at a faster rate than usual. It is clear that there is no point in transplanting a 50-year-old heart patient with 60-year-old cells

But in light of the results of the new study, researchers say the dream of producing organs for transplant now seems closer than ever. If a foreign organ is implanted in the body, the body immediately recognizes it and rejects it. Today, the problem is dealt with using drugs that prevent the rejection, but many times they have severe side effects.

Although the solution proposed by the researchers is far from being implemented, it is based on transplanting the patient's genetic load into an animal egg. At first it was thought that when a whole organ transplant was required, the patient would have to wait until the animal grew. But recent studies have shown that it is possible that the waiting time will be shortened significantly. This is because experiments show that it is possible to grow embryonic stem cells in the laboratory (embryonic cells that have not yet been differentiated according to individual roles) and create skin tissues, cartilage and even bladders. In any case, the body will recognize the organ as part of it, and will not reject it as happens with transplants today.

The cells of the cloned Dolly sheep aged at a faster rate than normal, and were older than cells of a normal sheep of the same age. The researchers are not sure what caused the cells of the cloned cows in the new study to be even younger than those of a cow of the same age. One of the obvious differences between the two clones is that the researchers used the cow clone in a very old cell.

It seems that the life span of cow cells is long compared to a normal cell. One of the main signs on which the researchers base this determination are the telomeres, which are at the ends of the chromosomes of each cell. Many researchers are convinced that the telomeres serve as the "stopwatch" of the cell, pacing its lifespan. At the beginning of its life, every cell has long telomeres. Every time it divides - and two cells are created from it - the telomeres shorten a little. Thus the process repeats itself, until the telomeres shorten almost completely, then the cell stops dividing and dies.

In one of the experiments, Lanza and his colleagues cloned five more embryos using the same method they used to clone six cows. They only let the embryos develop up to six weeks of age, to compare them in the lab to normal embryos. The cells of the cloned embryos divided 93 times, as opposed to 61 times in a normal embryo during such a period.

No one yet knows how to explain why the cells of the cloned cows have a longer lifespan. Dr. Lanza says that this may be due to the different type of cells used in the clones: udder cells in the case of "Dolly" compared to connective tissue cells in cows. The difference may be due to differences between the animal species, and perhaps also to additional differences in cloning methods. According to another hypothesis, the short telomeres in the nucleus of the transplanted cell (which was, as mentioned, very old) caused the fetus to "overcompensate" and grow longer telomeres than usual.

It is too early to determine whether the cloned cows will have a longer lifespan. To check this you have to wait a few more years, since cows live an average of twenty years.
But if later on in their lives it turns out that the cloning did affect their life expectancy as well, says Dr. Lanza, there is a "real possibility" that they will have a 50% longer life compared to normal cows. In terms of human life, it is about 150-100 years.

Other scientists are more cautious. They say that aging is a very complex process, and environmental and psychological factors also affect it.
{Appeared in Haaretz newspaper, 28/4/2000{

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