Figure 1.

Shelterin—The Border Security Force. The longstanding basic model posits that the six protein-complex directly associated with telomeres facilitates loop formation and protects it from illegitimate access by various factors, regulates access by the legitimate ones, and aids telomere replication. ‘t-loop’ stands for telomeric loop, while ‘D-loop’ stands for displacement loop. In mammalian cells, loss of shelterin proteins can lead to DDR, TRF2, and POT1 directly serving to inhibit ATM and ATR kinases, respectively, and a loss of TRF2 or POT1 would de-repress the association of ATM/ATR to the telomeres, resulting in senescence or apoptosis. Adapted from [42].