Forever young
IN AN exciting development, us researchers have discovered a "fountain of youth", albeit at a cellular level. The secret of everlasting youth, they say, is actually a DNA chain called telomerase. It is a cellular clock of sorts, winding down as the cells age. Its manipulation, say the researchers, can slow down the ageing process of a cell, and perhaps that of humans as well.
Researchers at the University of Texas's Southwestern Medical Center at Dallas, USA, and their colleagues at Geron Corporation, Menlo Park, California, USA, claim to have discovered a way to overcome cellular ageing and thus extend the life span of human cells. Woodring Wright and Jerry Shay say that the enzyme telomerase - a "cellular fountain of youth" - causes human cells grown in the laboratory to retain their "youthful vigour" and continue to divide long past the time when they normally stop dividing (Science, Vol 279, No 5349). Normal human cells have a limited capacity to proliferate. After a certain number of cell divisions, time on the biological clock runs out, the cells "age" and stop dividing. Time remaining in a cell's life correlates with the length of the telomerase -repeated sequences of DNA on the ends of chromosomes that protect the tips from degradation. In normal cells, telomerase shorten with each cell division. Although some have thought that this telomerase shortening might be the biological clock's control mechanism, the hypothesis was controversial. The research now proves that human cells grow older each time they divide because their telomerase shorten.
The scientists introduced telomerase into normal human cells to see if the cells' life spans could be prolonged.
The cells with telomerase extended the length of their telomerase, divided for 20 additional generations past the time they normally would stop dividing and are continuing to divide. They also grew and divided normally, giving rise to normal cells with the normal number of chromosomes.