Ageing and reproduction

Fri Apr 3 05:34:00 EST 1992

My first mail:

> > Gamete producing cells appear to constitute the only 'immortal' cell line.

... stuff deleted

> >Ageing is probably a side effect of differentiation,
> > most cells losing the immortality function found in the (undifferentiated?)
> > gamete-producing cells.

David Cooke replied:

> 	I don't see why the time of differentiation should make a
> difference in terms of DNA damage.  DNA gets damaged through chemical
> or radiation-induced mutations and through errors in replication.  Germ
> cells are likely to receive as much damage from chemical and radiation
> agents as any other cells in the body--that's basically a matter of

 If you damage a gamete too much it will probably be immediately lethal.
 Therefore no embryo. It is suspected that some 30% or more of all
 human conceptions don't get to the embryonic stage. Yes - gametes are
 liable to these environmental shocks. But the cell line doesn't "age".

> resemble it).  I think there's much more evidence to suggest that we
> get old because we are programmed to get old, not because we have to
> get old.

Yes - my point exactly. Differentiation of cells impiles the cell specialising
in a set of functions, at the expense of all the others. In gene-expression
terms this means inducing one set of genes and keeping all the others turned
off. Methylation of DNA occurs during embryogenesis. It is believed this is
part of the mechaism that shuts off gene expression permanently in some parts
of the genome.

I admit the gamete cell line is a special case. Maybe some differentiated
cell lines are just as 'immortal' and they get let down by the rest of the
body dying on them :-)


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