Many ways to telomere dysfunction: in vivo studies using mouse models.

The existence of a capping structure at the extremities of chromosomes was first deduced in the 1930s by Herman Müller (Müller, 1938), who showed that X-irradiation of Drosophila rarely resulted in terminal deletions or inversions of chromosomes, suggesting that chromosome ends have protective structures that distinguish them from broken chromosomes, which he named telomeres. In this review, we will focus on mammalian telomeres and, in particular, on the analysis of different mouse models for proteins that are important for telomere function, such as telomerase and various telomere-binding proteins. These murine models are helping us to understand the consequences of telomere dysfunction for cancer, aging and DNA repair, as well as, the molecular mechanisms by which telomeres exert their protective function.