cells counting off in culture

[Edward Krug]

One observation I have made of human fibroblasts in culture is that as 
they are reaching a high passage number they grow less well or rapidly, 
and provide a less nutrious host for a parasite I infect them with.  The 
point is that they gradually, over approximately half a dozen 
replications, they become exhausted.  If the shortening of the telomeres 
truns off selected genes, then it must be a leaky switch or one which 
inteferes with additional genes with each additional replication near the 
end of the cell's live.  Not an easy theory to prove.

Another observation which should be considered for mortal cells in 
culture, and that is that fibroblasts kept in a non-replicating state 
with low serum levels age even without replicating.  The number of 
doublings they are capable of deminishes even though they technically 
have not used up the lost potential.  There is clearly more to the story.

Unfortunately, I can not claim credit for these observations.

Edward C. Krug Ph.D.  E-mail= kruged at essex.hsc.colorado.edu
303-270-7234 (vox), 303-270-8681 (fax) Univ. of Colorado Med. School