Le, T.; Li, Y. M.; Saric, A.; Holthuis, J.; Grinstein, S.; Freeman, S.

The ubiquitous and highly conserved programmed cell death pathways that are essential for tissue homeostasis are accompanied by distinct morphological alterations. Apoptotic cells undergo fragmentation concomitant with the exposure of phosphatidylserine on the membrane surface. Large fragments, called apoptotic bodies, as well as much smaller vesicles are released. While the molecular mechanisms underlying apoptotic body formation have been explored, less is known about vesicle biogenesis. We used inducible, active forms of TMEM16F to determine the role of lipid scrambling in vesiculation. Plasmalemmal lipid scrambling sufficed to release apoptotic-like vesicles without causing changes in cytosolic calcium or the submembrane cytoskeleton. The scrambled bilayer showed pronounced segregation of exofacial lipids and redistribution of apparent cholesterol to the inner leaflet. The clustering of raft-associated components with bulky headgroups formed domains of outward (convex) curvature, while regions of accumulation of phosphatidylethanolamine generated inward (concave) curvature that facilitated the vesicle scission. Thus, scrambling of plasma membrane lipids suffices to induce regions of acute membrane curvature and facilitates detachment of vesicles analogous to those released from the surface of apoptotic cells.