Molecular manifestations and molecular determinants of telomere capping.
Multiple interacting components of the telomere, together with telomerase (and sometimes recombination), determine whether a telomere will be functional, allowing cell proliferation. The various components reinforce each other, providing for a robust and resilient system of protection and replenishment of telomeres. A characteristic of a telomere is that its structural features elicit responses that allow it to be dynamically recapped. Eliciting a DNA damage response through uncapping of a telomere appears to be one way in which telomerase action at that telomere is stimulated. Thus, as long as a timely and appropriate recapping of the telomere is possible, regulated uncapping of a telomere appears to be not only normal, but even required for optimal telomere maintenance. Telomere length and the presence of telomerase provide an example of a pair of interacting components that determine telomere capping function. Telomerase is dispensable in cells with sufficiently long telomeres; but in cells with short telomeres lacking telomerase, cells lose the ability to proliferate, and in some cell types, telomere fusions are increased. However, expressing telomerase can make even very short telomeres functional. Many interesting questions remain as to the mechanisms of these biological effects.