Platelets' preset lifespan

Platelets are born with a lit fuse. These clotting cells are set to implode when the fuse—its allotment of Bcl-x_L—is burnt up, based on findings from Kylie Mason, Benjamin Kile, David Huang, and colleagues (Walter and Eliza Hall Institute, Melbourne, Australia).

Life is short for platelets, which survive only about ten days before they are removed from the bloodstream. Platelet numbers are thus set by a balance between their production and removal. Mason et al. found that this balance shifted in mice with mutated versions of the antiapoptotic protein Bcl-x_L: the mice were severely deficient in platelet numbers.

An apoptotic-like mechanism is needed during the birth of platelets, which are shed from bone marrow megakaryocytes. “We thought this would be the problem,” says Kile, “but it's not.”...