I wanted to bring to your attention an interesting article in the
Tuesday, June 9th _New York Times_ Science Times Section (p. C1). It talks
about a possible relationship between telomere lengths and ageing, as well
as possibly cancer. I would highly recommend reading the original article,
but I'll summarize a few key points.
Telomeres are long chains of repeated 6 base-pair DNA sequences found
at the ends of chromosomes. They are apparently necessary for chromosome
stability; without them, chromosomes form abnormal associations and break up.
Telomeres apparently shorten by about 50 bp with each round of cell
division, and as a result they are much shorter in the elderly than in
children. It has been proposed that this is a mechanism by which cells can
tell how many times they have divided, and that cells with telomeres below
a certain minimum length die. Evidence for this theory is drawn from several
sources, including the observation that chromosomes are highly stable right
until the end, then suddenly fall apart. This can be interpreted as evidence
of a programmed event rather than gradual degeneration.
Telomeres are built up by an unique enzyme called telomerase. It is
very unusual in that carries an RNA template for the telomere sequence
(TTAGGG in humans) as part of its structure. Telmomerase is active all of the
time in paramecia and other simple species, but appears to be normally inactive
in human tissue except sperm cells, which have trace activity. The activity
in sperm is theorized to serve to keep the chromosomes in their most youthful
state.
There is suspicion that telomere length is related to some cancers.
Several research groups have claimed that telomere lengths can be used to
stage cancer cells: the shorter the the telomere, the more advanced the
malignancy. C.W. Greider and S.B. Bachetti et al. have reported in the
current issue of EMBO have found that immortalized cancer cells have active
telomerase and rebuild their telomeres, possibly accounting for their
immortality.
It has been suggested that telomerase-blocking drugs might be
effective against cancers. There also appears to be some similarity between
telomerase and reverse transcriptase; anti-reverse transcriptase agents are
being tested for anti-telomerase activity as possible anti-cancer agents.
The article goes into considerably more detail--look for it!
-David Cooke
dac at sci.ccny.cuny.edu
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David Aaron Cooke | ********************** | dac at sci.ccny.cuny.edu
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