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Cloned sheep shows signs of premature aging
Wonko42 writes "Everyone's favorite cloned sheep, Dolly, is showing signs of premature aging. Even though she's only three years old, her cells are acting like they're six years old. Scientists think this is because she was cloned using cells from an older sheep. "
Its been known for some time now that most cells don't live forever. I think it has actually been calcualted that human cells will only devide X numer of times before they stop working very well (where X is a number around 7x10^5 or so).
Some cells don't have this problem- noteably stem cells (the cells in your bone marrow from which all other cells come from) and cancerous cells. (!!!) I would have thought that Dolly would have been cloned from a stem cell. Maybe this was not possible when she was, uh, created.
The part of the article about telomeres is fairly accurate. Due to the way that DNA replicates, the ends of the chromosomes are not copied properly. There is an enzyme called telomerase that adresses this problem by capping the ends of the chromosome on each replication. (This also keeps the ends of the DNA from being degraded by enzymes in the cell's endoplasm). But telomerase doesn't do its job perfectly and the chromosome eventually starts to loose important parts of its DNA. How or even if this then triggers a self-destruct process in the cell is not really understood. Perhaps cloning can be used to study this.
2^5
The article points out that this may cause the sheep to die earlier than expected as all the cells are older. I would think that there would be other complications (or benefits) as well. As people age, their metabolism slows down. They also get wrinkly, smell funny, and go bald. Cloning of animals may finally help us to understand how aging works. Is it a result of time upon the body, or is it a result of genetics? We may even get some medical benefits as the body fights disease differently with age and we could start people off at an optimal age for immune system development (not being a doctor, this may well be birth).
:)
And if humans are ever cloned, what does this mean for things like Senior Citizen discounts and Social Security (I know this doesn't necessarily apply outside of the US). Is someone 65 years old because they've been on this planet for 65 years or because their cells say they're 65? Perhaps these old people who are climbing mountains and water skiing barefoot on one leg aren't really old, they've just been around for a while.
Some things to ponder:
What "apparent" age will the Dolly^2 have? Can we do any comparisons between Dolly, the original donor, and Dolly's clone? Is a clone of a clone even feasible?
Some of these are raised in the article. We live in interesting times!
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"May I have ten thousand marbles, please?"
The article that I read in the NY Times had some countervailing opinion. The size of the decrease is at the limits of the resolution of the measuring technique. We also don't know enough about natural variation in the size of telomeres to tell if the decrease is stastically significant.
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What is happening to Dolly's clones is a predictable event and one which did not surprise me at all. It simply proves a point.
Eucaryotes(aka multicellular life forms) have linear Chromosomes as opposed to prokaryotes(bacteria) which have circular chromosomes. Each time a linear chromasome replicates thru cell division, it losses some of its ends. This is called degenerate replication. An enzyme with an RNA core (used as a template) is used by the cell to replace the bases that can not be replicated and it is called Telomerase. The strech of DNA that is shortening is called the Telemere. Normally, telomerase is NOT active in cells other than in very early life(before the 2nd trimester). Although it has been found in some cells in the adult. Those cells are believed to be the pluripotent stem cells(capable of forming just about any cell in the body) and CANCER cells. If a cell wants to live forever, telomerase will have to reawaken and repair its ends if it does not, the belief in the scientific community is that the cell will undergo "Programmed death" (aka apoptosis) when the telemeres on the ends of the chromosome gets to short. An example of this principle can be seen in the disease ATAXIA TELANGIESIA (AT). These poor souls are born with abherently short telomeres and by the age of 18, the individuals resemble a 70 year old.
With that said, the DNA that was used for Dolly's clones was obtained from the breast of Dolly and the cells were fully differentiated and thus had already undergone significant shortening of the chromosome before the DNA was harvested. One would expect several things to happen. 1) DNA will age faster due to telemeric shortening and 2) DNA will have acumulated mutations from Dolly's life as well as from its own life and thus will have a higher disposition for cancer. I define cancer as the acuumulation of mutations that allows for genes to be disregulated and thus cells live when they should die. We have cells in our lab that were harvested from a lady named Helen ~30 years ago(Hela cells) and they are still alive and kicking while Helen is not. This cells are very screwed up(>90 chromasomes) and they have active telmerase.