Cell surface exposure of phosphatidylserine during apoptosis is phylogenetically conserved

Exposure of the aminophospholipid phosphatidylserine at the outer leaflet of the plasma membrane by apoptotic cells can trigger phagocytic removal of these dying cells. This functionality of phosphatidylserine exposure in the process of phagocytosis is indicated by in vitro studies of mammalian and insect phagocytes. We have studied the in vivo distribution of cell-surface exposed phosphatidylserine by injecting biotinylated Annexin V, a Ca 2+ -dependent phosphatidyl-serine binding protein, into viable mouse and chick embryos and Drosophila pupae. The apparent binding of Annexin V to cells with a morphology which is characteristicof apoptosis and which was present in regions of developmental cell death indicates that phosphatidylserine exposure by apoptotic cells is a phylogenetically conserved mechanism.