Fig. 1. Telomerase and cell division-dependent decrease in telomere length.

Chromosome telomere length and structural integrity in eukaryotic cells derived from fetal tissue are initially maintained by high levels of telomerase. Activity of this enzyme progressively decreases with each cycle of cell division, resulting in greatly shortened telomeres, decreased organization of chromatin and deleterious effects on cells, including cell division cycle arrest and cellular senescence (Campisi, [3]; Feng et al., [13]; Jaskelioff et al., [14]).