Each time they divide cells lose their telomeres, the specialized structures at the end of chromosomes, leading to senescence and death. By expressing telomerase, an enzyme that repairs telomeres but is not usually found in adults, cells were thought to become immortalized. But a new study shows that things are not so simple, in certain types of epithelial cell at least, where inactivation of the p16/retinoblastoma pathway is also needed.
