Regulation of telomerase activity throughout life: rescue effect or cancer
M.F. Haussmann, C.M. Vleck
Iowa State University, Department of Ecology, Evolution and Organismal Biology, 339 Science II, Ames, IA 50011, USA
The evolution of senescence is thought to follow from the progressive
decline in the force of natural selection after the onset of
reproduction. Cellular senescence caused by telomere shortening has
been suggested as one potential causal agent of aging. In some tissues,
telomeres are maintained by telomerase. The presence of telomerase
promotes tumor formation however, suggesting a trade-off between aging
and cancer. Weinstein and Ciszek's reserve-capacity hypothesis (2002)
suggests that the strategies organisms have evolved to cope with this
trade-off may vary with lifespan. I am testing the hypothesis that
species with short lifespans down-regulate telomerase throughout most
of life, until the end of life when critically short telomeres are
rescued by forced telomerase expression, possibly leading to an
increased incidence of cancer. Species with longer lifespans have a
slower rate of telomere shortening, possibly due regulated expression
of telomerase, and thus some risk of tumor formation throughout life. I
investigated telomerase activity in different tissues from hatchling,
young adult and old zebra finches (Taeniopygia guttata) to determine at
what age and in which tissues telomerase was expressed. In muscle,
liver and gonadal tissue telomerase activity was greater in old
individuals than in young adults, although generally activity was not
as high as in the hatchlings. This suggests a possible "rescue effect"
in old age, although we cannot rule out that this activity may indicate
neoplastic tissue. These results are in agreement with the
short-lifespan strategy. In the short-lived zebra finch, telomerase
expression maybe up-regulated in old age to rescue tissues with short
telomeres at the risk of tumor formation. We are now investigating the
telomerase profiles of avian species with long lifespans to determine
whether differential regulation of telomerase activity through life
coevolves with lifespan.
Key words:
bird, telomerase, telomere, aging, lifespan
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