George: Responding to your inquiry about telomeres I should say
that Allsop & Harley have found an average critical telomere
length to be 0-2kbp at the onset of senescence. Also, at onset of
senescense there are still many telomere sequences left on the
average but since telomeres are heterochromatic, the prevailing
theory is that the heterochromatin traps the first few genetic
bases which will become silent. Yes, at this point senility is
still reversible according to experimental evidence by J.W.Shay
and W.E.West because actual genetic sequences have not been lost
just yet. Your question about a senescent factor being expressed
is partially right, actually there is some evidence of an anti
senescent regulatory factor expressed by those first few genes
but when they become engulfed in heterochromatin they become
silent and senescence will occur. This is a hot area in biology
and its interesting to know that some people like yourself are
interested to learn more about whats making us old.
best regards,
Julio Karwoski