Kasprowicz et al. reveal that, in addition to its role in vesicle fission, dynamin helps recruit clathrin to the plasma membrane during the earliest stages of synaptic vesicle formation.
Neurons replenish their supply of synaptic vesicles by forming new vesicles from the presynaptic membrane, mostly via clathrin-mediated endocytosis. The dynamin GTPase helps separate internalizing vesicles from the plasma membrane. Accordingly, fly neurons expressing a temperature-sensitive dynamin mutant are unable to reform synaptic vesicles and accumulate deeply invaginated pits at restrictive temperatures. But temperature-sensitive dynamin might still be partially functional under these conditions, so Kasprowicz et al. completely inhibited the protein by photoinactivation.
Synaptic vesicle recycling was disrupted in fly neurons after dynamin photoinactivation, but, instead of accumulating deeply invaginated pits, the neurons accumulated large membrane cisternae that filled the cytoplasm of their presynaptic boutons. Similar cisternae accumulate in neurons upon clathrin inactivation, probably because the assembly of clathrin lattices on the presynaptic membrane prevents the membrane from being internalized via nonspecific, bulk endocytosis.
Using superresolution microscopy, Kasprowicz et al. found that neither clathrin nor its membrane adaptor α-adaptin was recruited to the presynaptic membrane when dynamin was photoinactivated or depleted by RNAi. Temperature-sensitive dynamin retained this ability to recruit clathrin, thereby inhibiting bulk membrane recycling and allowing clathrin-mediated endocytosis to proceed up to the vesicle fission step. Senior author Patrik Verstreken now wants to investigate how dynamin promotes assembly of the clathrin lattice.