Figure 2.

Unequal T-SCE delay senescence in telomerase-negative cells. This is an example of a single cell whose shortest telomere is just long enough to permit two cell divisions before senescence. As shown on the left side of the figure, if there is no T-SCE the cell produces an 8-cell colony at the time of clonal senescence. In contrast, the fate of the same cell would be quite different if an unequal T-SCE transferred most of the telomeric DNA to one daughter cell. The right side of the figure shows that one daughter cell senesces immediately, but the other cell proliferates for an additional two divisions and yields a 17-cell colony by the time proliferation ceases. Thus the effect of an unequal T-SCE is to delay clonal senescence.