X-Message-Number: 7775
Date: Fri, 28 Feb 1997 08:01:57 -0800 (PST)
From: Joseph Strout <>
Subject: Re: Clones and aging

> Message #7766
> From: 
> 
> Joe, you assume they have selected one cell out of several million to 
> clone that has not aged or has recovered from aging. Then you claim DNA 
> damage cause aging. Does that mean the DNA of mice are more often damaged
> than that of humans?

Yes.  Smaller animals, as a rule, have higher metabolism.  The primary
cause of damage to DNA is free radicals generated by metabolic processes.
Thus higher metabolism ==> faster aging.  This also explains why caloric
restriction retards aging: it slows metabolism.  (There are also
species-specific differences in mechanisms used to prevent or repair free
radical damage; thus, for example, pats live 5-10 times longer than mice
of similar metabolism.)  I'm no expert, but there was a recent review of
this stuff in Science, not more than a week or two ago.

> You also mention limited cell division. Has enough 
> Hayflick experiments been done with different animals e.g. mouse, horse and 
> turtle that one can draw a curve to demostrate his idea is correct for all
> animals. E.G. Mouse cell divides 3X, horse 18x and a turtle 200X or some 
> related ratio. I think not. And why not?

I mentioned it because you mentioned it.  I don't really believe it's the
key to aging, however.
 
> But let assume this was just an average cell they cloned would it not 
> mean all theories on aging will have to be revised?

I'm sorry, but I don't see how it relates.  Let's suppose that the
emerging consensus (metabolism --> free radicals --> DNA damage --> aging)
is correct.  How does the cloning experiment falsify this?  You might
argue that if the DNA is damaged, then it shouldn't produce a normal
offspring.  I'd agree, but what of it?  The DNA was probably not damaged,
because (1) the parent was probably a healthy young adult, not an elderly
one, and (2) when cells that had damaged DNA were tried, it didn't work.
The one that worked (and got into the news) had fine DNA.

,------------------------------------------------------------------.
|    Joseph J. Strout           Department of Neuroscience, UCSD   |
|               http://www-acs.ucsd.edu/~jstrout/  |
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