Deconstruction of the beaten Path-Sidestep interaction network provides insights into neuromuscular system development.

Abstract

An 'interactome' screen of all <i>Drosophila</i> cell-surface and secreted proteins containing immunoglobulin superfamily (IgSF) domains discovered a network formed by paralogs of Beaten Path (Beat) and Sidestep (Side), a ligand-receptor pair that is central to motor axon guidance. Here we describe a new method for interactome screening, the Bio-Plex Interactome Assay (BPIA), which allows identification of many interactions in a single sample. Using the BPIA, we 'deorphanized' four more members of the Beat-Side network. We confirmed interactions using surface plasmon resonance. The expression patterns of <i>beat</i> and <i>side</i> genes suggest that Beats are neuronal receptors for Sides expressed on peripheral tissues. <i>side-VI</i> is expressed in muscle fibers targeted by the ISNb nerve, as well as at growth cone choice points and synaptic targets for the ISN and TN nerves. <i>beat-V</i> genes, encoding Side-VI receptors, are expressed in ISNb and ISN motor neurons.