"Hayflick limit" in yeast and human germline

clejan clejan at jumpnet.com
Tue Sep 23 20:19:23 EST 1997

I have only recently become interested in the molecular biology of ageing, so please 
excuse my ignorance.

When I first read about yeast, the articles were saying that yeast is immortal, and 
were correlating this with the high levels of tellomerase found in yeast cells. Then 
I read Kennedy's recent article(I can't find it, but the first one I read was  in 
Cell, V80, 485-496, Feb 10 95)  which enlightened me to the fact that parents can be 
distinguished from offspring, and have a finite replicative capacity, despite the 
high levels of tellomerase. I thought that the same might be true of the human 
germline: the stem cells that become sperm have a finite capacity, but the "clock" 
gets reset for each generation, after the sperm penetrates the egg. But why is this 
different than somatic cells? 

Is there any experimental evidence showing that the stem cells that give rise to 
sperm ARE immortal in vitro? Can they be cultured and remain differentiated?

This whole subject is fascinating. I should have gone into biology instead of 

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