counting cell divisions in vivo

[James]

>To the extent that one thinks the Hayflick limit has to do with aging,
>it seems one would want to study cell division in vivo--and to study
>whether the tissues of long-lived animals (say on calorie restricted
>diets) had cells that could divide a larger number of times
>(defying/extending the Haflick limit) or divide more slowly through life
>(reenforcing a "magic-number" interpretation of the Hayflick limit =>
>aging idea).


How do you study cell division (and count it) in vivo?  It has been known
for a long time that in vitro there is a correlation with the lifespan of an
animal and the number of times its cells can divide, but I don't think there
is any good way to do this in vivo.

James