A study conducted at IFOM in Milan has revealed that there are regions of the genome that are completely undefended. They are the telomeres, or extremities of the chromosomes that, by shortening with each cellular proliferation cycle, mark the inexorable passage of time and lead to cellular aging. A discovery by the team of scientists led by Fabrizio d’Adda di Fagagna at IFOM now clarifies how these cellular clocks are irreparable, independently of their shortening. In other zones of the genome efficient repair systems go to work when needed, but not here. Here the signs remain of any damage that the cell may suffer to its DNA during the course of its life. Here lesions accumulate during the aging of the organism, its tissues and cells. But if, on one hand, senescence marks the deterioration of an entire series of vital functions, on the other hand, at the cellular level, it is also a mechanism that can prevent the onset of tumours when activated precociously. The details of this research have been published online yesterday, 19th March 2012, in the authoritative scientific journal Nature Cell Biology.