The phenomenon of limited cellular division was first observed by
, and is now referred to as the
. Significant discoveries were made by the team led by Professor
University of California, San Francisco
Advocates of human
promote the idea of lengthening the telomeres in certain cells through temporary activation of telomerase (by drugs), or possibly permanently by
. They reason that this would extend human life because it would extend the Hayflick limit. So far these ideas have not been proven in humans, but it has been demonstrated that telomere extension has successfully reversed some signs of aging in laboratory mice
However, it has been hypothesized that longer telomeres and especially telomerase activation might cause increased cancer (e.g. Weinstein and Ciszek, 2002). However, longer telomeres might also protect against cancer, because short telomeres are associated with cancer. It has also been suggested that longer telomeres might cause increased energy consumption.
Techniques to extend telomeres could be useful for
, because they might permit healthy, noncancerous mammalian cells to be cultured in amounts large enough to be engineering materials for biomedical repairs.
That the role of telomeres is far from being understood is demonstrated by two recent studies on long-lived
. In 2003, scientists observed that the telomeres of
) seem to lengthen with chronological age, the first observed instance of such behaviour of telomeres.
In 2006, Juola
reported that in another unrelated, long-lived seabird species, the
), telomere length did decrease until at least c.40 years of age (i.e. probably over the entire lifespan), but the speed of decrease slowed down massively with increasing ages, and that rates of telomere length decrease varied strongly between individual birds. They concluded that in this species (and probably in
and their relatives in general), telomere length could not be used to determine a bird's age sufficiently well. Thus, it seems that there is much more variation in the behavior of telomere length than initially believed.
The telomere length varies in cloned animals. Sometimes the clones end up with shorter telomeres since the DNA has already divided countless times. Occasionally, the telomeres in a clone's DNA are longer because they get "reprogrammed"[