Must an AGING PROCESS be universal?

Andrew K. Groves grovesa at starbase1.caltech.edu
Mon Apr 3 17:09:51 EST 1995


In article <3lodlg$5hp at mserv1.dl.ac.uk>, <W.G.VAN.DOORN at ATO.AGRO.NL> wrote:

>      The next question is how old do individual cells really get. I wouldlike
>      to ask for sound proof, derived from individually tagged cells, showing
>      their age. Andy thinks that the stem cells in the intestine live as long
>      as the individual human being. If this is true the maximum age of an 
>      individual cell is at least 120 years. Can anyone add to this list, but 
>      please only when also quoting the paper in which it has been 
>      published. For me the list has not yet started, as I would like to know
>      whether the intestine stem cells live that long for a fact.          
>      

I think there is a misunderstanding here, although I'm not sure. A gut
stem cell (to use the above example) divides, giving rise to two daughter
cells - one of which is another stem cell, the other will go on and give
rise to differentiated cells in the gut wall. So an 'individual' cell
doesn't live for 120 years, although the propagation of the stem cell
population does indeed occur, presumably as long as the gut remains
intact. I don't see how you could do the tagging experiment you propose,
not least because gut stem cells have never been unequivocally identified
- their existence is inferred from the kinetics of gut wall shedding and
renewal. 

As far as normal cells (as opposed to cell lines) being propagated beyond
their normal limit, there is a fair amount of data that this can be
achieved in culture. For example, glial progenitor cells (O-2A cells) can
be grown in culture, but they normally tend to differentiate and stop
dividing after a period of (about ) 10 divisions. If, on the other hand
you grow similar primary cultures of these cells in a combination of
platelet-derived growth factor and fibroblast growth factor, they can be
propagated for months. If you withdraw these factors, the cells tend to
differentiate immediately, suggesting that the effect of these two factors
is reversible. It has been possible to expand such glial precursors, and
to transplant them into animals, where they appear to differentiate
normally without giving tumours. But this is more Oliver Bogler's
speciality than mine, so I'll leave it to him to elaborate further if he
sees fit.


Regards,

Andy Groves

-- 
Andy Groves
Division of Biology, 216-76
California Institute of Technology




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