In article <3ljpem$ldr at mserv1.dl.ac.uk>, <W.G.VAN.DOORN at ATO.AGRO.NL> wrote:
> Andy - my point is that, until proven differently, aging should be considered
> universal. Some cells may divide quite a few times, but will eventually stop
> and die. Strange enough, evolution has not shown an escape from this route.
I disagree, and cite my examples of stem cells in bone marrow, gut and
skin. These cells do not appear to have a limit on the number of times
that they can divide in the living animal. Of course, if the animal itself
dies - (gets shot, catches pneumonia, jumps off a building), then those
stem cells will obviously die too. There are dividing stem cells in the
gut of 120 year old humans, and there is no reason to think that they have
a limit on division.
I stress this by way of comparison to cells that have a "Hayflick" limit
(from the work of Hayflick, Moorhead, Todaro and Green, among others).
Some cells in an animal DO have a seemingly pre-programmed number of
divisions, and will eventually stop dividing. They won't necessarily die -
they will just be unable to divide. Stem cells in the gut, bone marrow and
skin do not behave like this, even though the differentiated progeny to
which they give rise do.
Division of Biology, 216-76
California Institute of Technology