Neurexin directs partner-specific synaptic connectivity in C. elegans

Abstract

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.

Dendritic spines on GABAergic neurons respond to cholinergic signaling in theCaenorhabditis elegansmotor circuit

“…For super-resolution imaging, we used the synaptic vesicleassociated marker, mCherry::RAB-3, to label the presynaptic termini of VA and VB class cholinergic motor neurons in the ventral cord and LifeAct::GFP to label DD neurites and spines ( Figure 2B). Clusters of mCherry::RAB-3-labeled puncta are located adjacent to DD spines ( Figure 2B) 13 . Among the 128 spines identified by LifeAct::GFP, most (~84 %) reside near at least one presynaptic cluster (denoted "contacted" in Figure 2D) 13 .…”

“…Clusters of mCherry::RAB-3-labeled puncta are located adjacent to DD spines ( Figure 2B) 13 . Among the 128 spines identified by LifeAct::GFP, most (~84 %) reside near at least one presynaptic cluster (denoted "contacted" in Figure 2D) 13 . Approximately ~40% (51/128) of DD spines are associated with multiple presynaptic clusters of RAB-3 puncta which suggests that individual spines receive input from > 1 presynaptic terminal (arrowheads, Figure 2B).…”

“…The acetylcholine receptor (AChR) subunit ACR-12 is postsynaptic to cholinergic inputs at GABAergic motor neurons, and has been previously shown to localize to DD1 dendritic protrusions ( Figure 2E) 13,38,39 . We used AiryScan imaging to quantify the subcellular distribution of the ACR-12::GFP signal on DD spines.…”

“…Subsequent work using light and electron microscopy detected similar dendritic protrusions extending from D-class motor neurons in the related nematode, Ascaris 11,12 . Finally, a recent report used light microscopy to show that a postsynaptic acetylcholine receptor is localized near the tips of spine-like protrusions on DD class motor neurons that directly appose presynaptic termini 13,14 . Here, we have adopted a systematic approach to test the hypothesis that these spine-like structures in C. elegans GABAergic motor neurons (DD and VD) exhibit the salient hallmarks of dendritic spines in mammalian neurons.…”

Gain-of-function mutations in the UNC-2/CaV2α channel lead to hyperactivity and excitation-dominant synaptic transmission in Caenorhabditis elegans

“…Cholinergic motor neurons simultaneously innervate body wall muscles and GABAergic motor neurons (White et al, 1986). Both acr-12 and unc-29 are also expressed by GABAergic motor neurons, and play a role in cholinergic activation of not only body wall muscles, but also GABA motor neurons (Petrash et al, 2013;Philbrook et al, 2018). However, GABA signaling was not required for UNC-49/GABA A R expression or localization in body wall muscles (Gally and Bessereau, 2003).…”