Hello, Sidney Shall,
Thank you for your reply about the Hayflick limit.
My thought was that the Hayflick limit turned out to spurious due to improper
culture techniques (poor nutrition or contamination). While _some_
of the evidence you mentioned (which I abstracted from your posts for
presentation and comment below) does imply the existence of a Hayflick limit,
it is not yet clear in my mind that _all_ of the evidence you advanced implies
a genetically determined limit that would also exist in vivo. Perhaps you
would be kind enough to post further explanations to aid my understanding.
I don't think you mentioned in vivo tests, but I'll bring that subject up.
One can still interpret the aging differences between in vivo and
in vitro as an artifact of inadequate culture technique, if the nutrition
delivery and waste/immune system disposal systems??? of in vivo differ from
and are probably better than what scientists are now able to provide in vitro.
So what I am suggesting is that there may indeed be a genetically related
Hayflick limit that occurs with in vitro testing, but that such a limit
may not exist in vivo, or if it does, perhaps not to an extent that explains
the sensescence of man. I am ignorant of whatever in vivo testing may have
been done to explore this.
In 2 replies to 2 persons' queries on Hayflick limits you wrote (I have deleted
what I think is not essential to this my current post, and added numbers):
|| From: bafa1 at central.susx.ac.uk (Sydney Shall)
| Organization: University of Sussex
|| [1]
| No, the hayflick limit is NOT due to culture techniques.
| ...when the same cell types, from different species are
| grown under identical conditions with the identical solutions in the
| same incubator, quite different Hayflick limits are observed. The
| observation is quite good evidence that the Hayflick limit is due to the
| cells and not to the medium. ...
I fail to see your conclusion in [1]. One simple and perhaps wrong
explanation will serve to illustrate: Suppose the metabolism of the
different cell types proceeds at different rates, but that they all
require something that is inadequately provided by the culture
technique, perhaps nutrition or waste disposal. There would be
a genetic link, expressed thropugh different rates of metabolism, but
the inadequate culture technique could be the cause of existence
of the (different) Hayflick limits. The magnitude of the differences
would be genetically related, but the _existence_ of the limit would be
because of the culture technique.
|| [2]
| The second line of evidence is the
| existence of human genetic disorders like Werner's syndrome, which is a
| premature ageing disease, in which the identical cells to a normal
| control, in the same mediium in the same incubator, do in fact grow as
| much as 1000 times less than the control cells. This again makes it
| clear that the hayflick limit is due the cells and not the medium. ...
Again , by similar reasoning, I fail to see your conclusion in [2].
|| [3]
| Finally, one can grow normal cells and observe an Hayflick limit and
| tumour cells and not observe any limit; in the same medium and
| incubator. ...
Now this seems to me to be the most solid evidence, except I still
wonder: could tumor cells have requirements for metabolism that
are in _some_ respects less demanding than normal cells?
|| [4]
| Cells from different tissues display different Hayflick
| limits. ... ... the evidence available so far would suggest
| that there are specific Hayflick limits for different tissues.
Again, my objection is the same as for [1].
|| [5]
| In general therefore, the hayflick limit is a biological
| phenomenon, and not a culture artifact. ...
| This evidence given above does not prove that the culture conditions are
| totally irrelevant to the way normal cells grow in culture; the culture
| conditions very clearly do modulate the growth rate and the Hayflick
| limit, but only within narrow boundaries.
|| --
| Sydney SHALL,
| Laboratory of Cell and Molecular Biology,
| Biology Building, Univ. of Sussex, Brighton, East Sussex BN1 9QG, ENGLAND
| Telephone: +44.273.67.83.03 FAX: +44.273.67.84.33
|
So I hope you can lay to rest my uneasiness with your previous explanations,
and also shed some light on whatever testing may have been done in vivo for
establishing Hayflick limits. I am sure the topic is a good one
for this bulletin board. Thank you for your time....
Norm Andrews, AT&T, norm at chico.wh.att.com
