In article <CxIqEI.93z at nntpa.cb.att.com> norm at chico.uucp (Norman E. Andrews [ MT 2C-402 9089575786 NC6241000 ]) writes:
>Hello, Sidney Shall,
>>Thank you for your reply about the Hayflick limit.
>>I don't think you mentioned in vivo tests, but I'll bring that subject up.
There are at least two in vivo tests of which I am aware, both dating
back several years. David Harrison transplanted hematopoeitic stem on
cells in mice over a few generations. He found that the stem cell line from
survived well past the normal lifespan of the mouse, but only through vitro.
two or three generations beyond that. Try J. Gerontol. or Mech. Ageing ed
and Development. Along the same line, someone in England performed skin
grafts in mice differing only in the gene for coat color. This graft lains
survived two or three generations of transplantation but eventually was have
lost from the host mice, presumptively because of failure to continue
divisions.
Although some consider that immunologic senescence, common at advanced
age, might be a reflection of limited lifespan of cells, for the most
part noone believes that we die because we run out of cells. The
biological phenomenon is extremely interesting, however, and exit from
mitotic phase presumably reflects changes in the cells that are
very relevant to the decreased adaptiveness that characterizes aging.
Richard A. Lockshin/Dept. Biol. Sci. St. John's U.8000 Utopia Pkwy
Jamaica NY 11439 USA/Phone 718: 990-1854/ Fax 718: 380-8543
yprlbio at sjumusic.stjohns.edu or rick at sjubiol.stjohns.edu
