Bruchpilot, a protein with homology to ELKS/CAST, is required for structural integrity and function of synaptic active zones in Drosophila

Summary Neurotransmitters are released at presynaptic active zones (AZs). In the fly Drosophila , monoclonal antibody (MAB) nc82 specifically labels AZs. We employ nc82 to identify Bruchpilot protein (BRP) as a previously unknown AZ component. BRP shows homology to human AZ protein ELKS/CAST/ERC, which binds RIM1 in a complex with Bassoon and Munc13-1. The C terminus of BRP displays structural similarities to multifunctional cytoskeletal proteins. During development, transcription of the bruchpilot locus ( brp ) coincides with neuronal differentiation. Panneural reduction of BRP expression by RNAi constructs permits a first functional characterization of this large AZ protein: larvae show reduced evoked but normal spontaneous transmission at neuromuscular junctions. In adults, we observe loss of T bars at active zones, absence of synaptic components in electroretinogram, locomotor inactivity, and unstable flight (hence " bruchpilot "—crash pilot). We propose that BRP is critical for intact AZ structure and normal-evoked neurotransmitter release at chemical synapses of Drosophila .