(Re telomerase-less mice)
>I must admit that I would also expect the mice to have severe reproductive
>difficulties, but if they really have gone through 4 generations then the
>trouble can't be too bad. This probably means that we really don't understand
>what's going on very well. Lots about this puzzle seem contradictory, but the
>parts must fit together somehow.
One possible explaination is that mice achieve senescence via a different
mechanism. They would then have no compelling need to use telomerase to
keep differentiated cells on a tight leash; they could have a backup system
or just long enough telomeres to tolerate lots of divisions.