The second puzzle arose following discovery of how DNA copies itself. The process cannot copy the very ends of the chromosomes. So if the DNA is copied repeatedly (as in development, when DNA of one cell is copied in all subsequent cells) the chromosome eventually shortens so much that the cells are no longer viable.
Researchers surmised that something unusual was occurring at the ends of the chromosomes, known as telomeres.
Using animal models developed by Dr. Gall, Dr. Blackburn, then a research fellow in his lab at Yale, discovered a special DNA sequence TTAGGG in humans that is found nearly identically at the telomeres of nearly every type of animal and plant species. The telomeres protect the ends of the chromosomes and prevent them from opening up, which could result in separation of the two strands of DNA. Thus, the telomeres act as clamps on the ends of the chromosomes. In humans, there are thousands of these segments at the end of a chromosome.
Later, in Dr. Blackburns laboratory at the University of California at Berkeley, she and Dr. Carol Grieder, then a research fellow, discovered an enzyme central to aging and cancer, which they named telomerase.
Though Drs. Gall, Blackburn and Greider did not set out to answer questions about aging, telomerase has provided answers. The sequencing of the telomeres and the discovery of telomerase has lead to an entirely new field of research that has yielded insights into the mechanisms of aging and the causes of cancer.
Because most human cells have limited amounts of telomerase, they have a limited lifespan. Adding telomerase to human cells in culture dishes makes cells immortal, giving telomerase a dark side: almost all cancer cells produce telomerase to fuel their uncontrollable proliferation. Drugs that inhibit telomerase are currently being sought as potential new treatme
|Contact: Elizabeth Streich|
Columbia University Medical Center