Hayflick limit wrong ?
Andrew K. Groves
grovesa at starbase1.caltech.edu
Mon Apr 25 16:22:41 EST 1994
In article <2pgrb1$p2o at mserv1.dl.ac.uk>, "Leonid Gavrilov"
<gavrilov at aeiveos.uucp.free.msk.su> wrote:
> Dear AGEING LIST subscribers,
> I would like to know the current situation for the discovery of the
> authors mentioned below, that simple change of composition of the cell
> culture medium could eliminate cellular senescence:
> Loo, D.T., Fuquay, J.I., Rawson, C.L. and Barnes, D.W. (1987).
> Extended culture of mouse embryo cells without senescence: inhibition by
> serum. Science 236, 200-202.
> These authors demonstrated that normal diploid mouse embryo cells, which
> under standard conditions manifest a growth crisis after 7-10 population
> doublings, may be successfully cultivated without any sign of an
> approaching growth crisis for at least 200 population doublings. All that is
> necessary is to change the composition of the culture medium (excluding
> blood serum and adding a number of ingredients, including the epidermal
> growth factor). In this case the cells, which are apparently capable of
> unlimited multiplication, remain diploid and nontumorigenic.
> If that is true, then the claim of Dr.Hayflick that all diploid cells
> have intrinsic limit to cell division, is definitely wrong.
> Does anybody know whether the results of these authors were reproduced
> or disproved ?
That paper hasn't been 'disproved' as such, but the findings have been put
in a different perspective. In 1990 David Barnes' group published another
paper showing that the cells referred to in their Science paper could be
induced to express GFAP (glial fibrillary acidic protein) in the presence
of serum or TGF-beta. The reference is Sakai et al., PNAS 87 8378-8392.
In the original Science paper, I believe the authors simply took mouse
embryo carcasses (including the head and spinal cord) and grew them in
their defined medium. In the light of the induction of GFAP, it would
appear that what they were growing were not fibroblasts (as in the Hayflick
and Moorhead work), but rather astrocyte precursors.
There are quite a few reports of precursor cells being able to proliferate
for long periods of time in defined medium containing growth factors. For
example, Reynolds and Weiss (Science 255, 1707-1710, 1992) could grow a
neural precursor cell for long periods in EGF. Bogler et al. (PNAS 87
6368-6372, 1990) were able to grow oligodendrocyte-type-2 astrocyte
progenitor cells in PDGF and FGF for many months.
I have often wondered what results the Barnes group would have obtained if
they had removed the nervous tissue from their mouse embryos. To my
knowledge, there is no data to suggest that fibroblasts can be cultivated
in defined medium indefinitely without transformation - although I would be
happy to be proved wrong.
I hope this is helpful.
Division of Biology, 216-76
California Institute of Technology
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