Synaptic Vesicle Tethering to the Drosophila Active Zone Cytomatrix

Bruchpilot (Brp) is a core protein component of the Drosophila active zone (AZ), where it promotes calcium channel clustering to ensure adequate transmitter release. In addition, the C-terminal region of Brp tethers synaptic vesicles to the AZ cytomatrix. In a C-terminally truncated allele, brpnude (lacking the last 17 amino acids), impaired vesicle tethering is accompanied by short-term synaptic depression and impaired sustained transmitter release. We set out to test the hypothesis that neuronal expression of a C-terminal Brp fragment would mimic the synaptic phenotype of brpnude mutants by competitively binding the putative vesicular interaction partner(s) of Brp. Our electrophysiological analysis of larval neuromuscular synapses supports this hypothesis and sets the basis for a subsequent in vivo screen to identify the interacting protein(s). To this end, a membrane-bound C-terminal Brp fragment was neuronally expressed to misdirect synaptic vesicles to ectopic locations. RNAi lines against vesicle-associated proteins were then scored for their ability to revert the ectopic vesicle localisation.