Bulk endocytosis at the synapse: role of Dap160

The recycling of synaptic vesicles at the synaptic periactive zone (PAZ) is mainly achieved by clathrin-mediated endocytosis and bulk endocytosis. The endocytotic factors executing these events such as the GTPase dynamin are controlled by large scaffolding proteins that include dynamin-associated protein of 160 kDa (Dap160) in Drosophila (Intersectin in mammals). Dap160 has been suggested to coordinate dynamin’s function at the PAZ through interactions that involve several of its SH3 domains, but the exact roles of these domains are not understood. Here (p. 1021), Oleg Shupliakov and colleagues use expression of Dap160 mutants lacking SH3 domains A and B (ΔAB) to investigate the molecular basis for the control of dynamin by Dap160. They find that under rest conditions, Dap160 and dynamin colocalize to the distal pool of synaptic vesicles and together relocate to the PAZ during synaptic activity. However, ΔAB mutants are unable to accumulate dynamin at the PAZ during stimulation and large bulk endocytic structures and vesicles accumulate in this synaptic region, but, interestingly, clathrin-mediated endocytosis is unaffected. Moreover, the authors show that the lack of SH3 domains does not affect the development of the neuromuscular junction, which indicates that the architectural role of Dap160 is separate, and mediated through other protein domains. Taken together, these data reveal new insights into the role of Dap160 in suppressing bulk endocytosis at the synapse.