Telomeres are distal ends of human chromosomes composed of tandem repeats of the sequence TTAGGG. Possible functions of telomeres include prevention of chromosome degradation, end-to-end fusions, rearrangements, and chromosome loss. Human telomeres in somatic cells undergo progressive shortening with cell division, presumably caused by the inability of cells to fully replicate the ends of linear DNA templates (1 ). When telomeres reach a critically short length with aging of cells, the cells exit from the cell cycle and stop dividing, so-called replicative senescence (2 ,3 ).
