Synaptic vesicle size and number are regulated by a clathrin adaptor protein required for endocytosis

Clathrin-mediated endocytosis is thought to involve the activity of the cla thrin adaptor protein AP180. However, the role of this protein in endocytos is in vivo remains unknown. Here, we show that a mutation that eliminates a n AP180 homolog (LAP) in Drosophila severely impairs the efficiency of syna ptic vesicle endocytosis and alters the normal localization of clathrin in nerve terminals. Most importantly, the size of both synaptic vesicles and q uanta is significantly increased in lap mutants. These results provide nove l insights into the molecular mechanism of endocytosis and reveal a role fo r AP180 in regulating vesicle size through a clathrin-dependent reassembly process.