For all animals, eliminating some cells is a necessary part of embryonic development. Living cells are also naturally sloughed off in mature tissues; for example, the lining of the intestine turns over every few days.
One way that organisms get rid of unneeded cells is through a process called extrusion, which allows cells to be squeezed out of a layer of tissue without disrupting the layer of cells left behind. MIT biologists have now discovered that this process is triggered when cells are unable to replicate their DNA during cell division.
