In neural circuits, individual neurons often make projections onto multiple postsynaptic partners. Here, we investigate molecular mechanisms by which these divergent connections are generated, using dyadic synapses in C. elegans as a model. We report that C. elegans nrx-1/neurexin directs divergent connectivity through differential actions at synapses with partnering neurons and muscles. We show that cholinergic outputs onto neurons are, unexpectedly, located at previously undefined spine-like protrusions from GABAergic dendrites. Both these spine-like features and cholinergic receptor clustering are strikingly disrupted in the absence of nrx-1. Excitatory transmission onto GABAergic neurons, but not neuromuscular transmission, is also disrupted. Our data indicate that NRX-1 located at presynaptic sites specifically directs postsynaptic development in GABAergic neurons. Our findings provide evidence that individual neurons can direct differential patterns of connectivity with their post-synaptic partners through partner-specific utilization of synaptic organizers, offering a novel view into molecular control of divergent connectivity.
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Philbrook, A.; Ramachandran, S.; Lambert, C. M. ; Oliver, D.; Florman, J.; Alkema, M. J. ; Lemons, M.; and Francis, M. M. (2018). Neurexin Directs Partner-Specific Synaptic Connectivity in C. elegans. eLife 7: e35692. https://doi.org/10.7554/eLife.35692.001