Three US scientists have won this year's Nobel prize for Medicine or Physiology for their work on how DNA protects itself from degradation, the Nobel Assembly at Sweden's Karolinska Institute announced on 5 October. Their discoveries 'have added a new dimension to our understanding of the cell, shed light on disease mechanisms, and stimulated the development of potential new therapies', the Assembly said.
Professor Elizabeth Blackburn, now at the University of California in San Francisco, US, first identified a typical sequence of DNA molecules (CCCCAA) that was repeated at the end caps of chromosomes - called telomeres - in a unicellular organism, in 1980. It later became apparent that variations of this same telomere sequence are present in most plants and animals. Professor Jack Szostak, now at Harvard Medical School and Howard Hughes Medical Institute, attached this sequence to chromosomes that normally deteriorate rapidly in yeast cells, and found that this prevented them from degrading. Professor Carol Greider - then a graduate student supervised by Professor Blackburn, but now at Johns Hopkins University in Baltimore, US - subsequently discovered telomerase, an enzyme that extends the telomeres, in 1984.
Every time a cell divides, its telomeres become progressively shorter, because the enzymes that copy the rest of the genetic material cannot copy the very end of the chromosome. This means that most cells can only divide a certain number of times, before the telomeres reach a critically short length that stops further cell divisions. However, in cells where the enzyme telomerase is active - such as stem cells and germ cells - it acts to restore shortened telomeres.
Later research by the Nobel Prize winners shows that cells with damaged telomerase age faster, and aging of human cells is delayed by the presence of telomerase. Sadly, this does not mean that flooding our cells with telomerase is a good way of increasing their life span. Excessive telomerase activity causes other problems; cancer cells have the ability to divide infinitely without reducing their telomeres. As such, research on telomeres has led to the development of new cancer vaccines directed against cells with increased telomerase activity. Some other diseases such as congenital aplastic anemia, a blood disease, have also been linked to damaged telomerase.
Professor Blackburn has also been active in science policy, particularly in the field of human embryonic stem cell research. In 2004, her membership of George W. Bush's President's Council on Bioethics was not renewed, after she had criticised the Council for presenting biased scientific information in its report 'Human Cloning and Human Dignity: An Ethical Inquiry'. President Bush was strongly criticised by many bioethicists, scientists and politicians for this politically motivated 'reshuffle' of the Council.
