Figure 2. Origin of intracellular vesicles.

(A) First, uniformity of the unilamellar membrane structure is disturbed and phospholipids accumulate along the membrane. (B) Small intracellular vesicles are always generated in direct proximity to these lipid domains (left), and cytoplasmic material of the maternal cell is encapsulated into the vesicles as visualized by the compartmentalization of GFP (right). Membranes stained with CellTrace BODIPY TR methyl ester and cytoplasmic GFP fluorescence are shown in red and green, respectively. All images are confocal. (D) Current model for vesicle genesis. Lipid accumulations act as a pool for incorporation of phospholipids into a membrane structure, resulting in enlargement of intracellular progeny vesicles by a self-organizing, spontaneous process typical for bipolar phospholipids.