In article <jcherwon.148.3326EBB5 at dres.dnd.ca>,
John Cherwonogrodzky <jcherwon at dres.dnd.ca> wrote:
>- Does this occur in all tissues, or are sperm and egg chromosomes spared
>telomere shortening (otherwise the fetus would have an extremely short
Telomerase is activated somewhere in the germline and possibly in the
embryo. That means that sperm and egg telomeres are longer than in the
rest of the tissues. There are also some foci in adult tissues where very
low levels of telomerase have been detected; it isn't clear what the
functional significance of this is. It's plausible that some very early
stem cells may have activated telomerase, but this is hypothetical.
>- Do fetus or cancer cells have a method for telomere repair and lengthening?
Fetus isn't clear. Maybe. As I say the germline cells have activated
telomerase (the enzyme which extends the telomeres, of course) so yer,
there is such a mechanism. Cancer cells have predominately activated
telomerase: there are many articles demonstrating this, both in vivo and
in vitro.
>- Given that "Dolly" was a clone of an udder cell from a 6 year old sheep,
>would one expect that Dolly will have a lifespan shortened by 6 years or one
>that is as long as her "mother"?
This is even less clear. Although IN HUMANS it's likely that telomerase
is an important mechanism for limiting cell lifespan, this is NOT a
universal thing across species. Lab mice, for example, have extremely
long telomeres which are less likely to play an important role in aging of
the cells. (Even very old mice have telomeres which are much longer than
human children.) It's simply not known what sheep and cattle do with
their telomeres, so your question in unanswerable without more data.
And, in fact, if you look carefully at the full article in which Wilmut et
al describe the technique (which article, by the way, doesn't use the word
"cloning" at all, as far as I could see) they mention that one possible
use for this technique is to help clarfiy the role of telomeres and
telomerase in cell aging.
Ian
--
Ian York (iayork at panix.com) <http://www.panix.com/~iayork/>
"-but as he was a York, I am rather inclined to suppose him a
very respectable Man." -Jane Austen, The History of England
