The cloning of the sheep has certainly opened a number of questions
about the regulation of lifespan and the critical aging signal. The
possibilty importance of methylation was mentioned. Alternate
methylation patterns in maternal and paternal gametes have been
suggested as critical for development but the cloning of the sheep
clearly doesn't require gamete methylation programing. The suggestion of
methylation as important to ageing is likewise defeated by the sheep. In
both cases the presumed crucial methylation is a property of the "old"
nucleus but development apparently proceeds normally. I believe that
implicates the programming of the egg as critical.
Does the ageing signal reside in the nucleus? If the ageing "clock" is
nuclear, DNA damage or telomere lenth have been proposed, then Dolly is
a problem. Perhaps the successful fusion contains not the odd undamaged
nucleus but a nucleus that has lost genes critical to sensing ageing. It
will be interesting to see if clones have an elevated cancer incidence.
