Flying kites on slippery slopes at Keystone : Symposium on lipid rafts and cell function

The fluid-mosaic model of the plasma membrane, proposed by Singer and Nicolson in the early 1970s (Singer & Nicolson, 1972), has provided a powerful driving force for understanding the structure of the cell membrane. Studies of the temporal and spatial architecture of the plasma membrane have indicated that it consists of compartments, which are probably maintained through their interaction with the underlying cortical cytoskeleton meshwork (Edidin, 2003; Kusumi et al, 2005). The membrane raft hypothesis was originally proposed by Simons and van Meer to explain the segregation of lipids and membrane proteins during their delivery and distribution in polarized epithelium (Simons & van Meer, 1988). This hypothesis—according to which specific lipids dynamically associate with each other to form platforms that are important for membrane-protein sorting and the formation of signalling complexes—was then integrated with the observed compartments (Simons & Toomre, 2000). Subsequently, this type of compartmentalization was related to studies of artificial membranes showing phase segregation behaviour, in which lipids in a fluid bilayer separate into domains containing molecules that display more or less ordered organization in terms of correlation with the orientation of neighbouring molecules (Simons & Vaz, 2004).