Kinesin-3 mediated axonal delivery of presynaptic neurexin stabilizes dendritic spines and postsynaptic components

Abstract

A high degree of cell and circuit-specific regulation has complicated efforts to precisely define roles for synaptic adhesion proteins in establishing circuit connectivity. Here, we take advantage of the strengths of C. elegans for cell-specific analyses to investigate molecular coordination of pre- and postsynaptic development. We show that developing dendritic spines emerge from the dendrites of wild type GABAergic motor neurons following the localization of active zone proteins and the formation of immature synaptic vesicle assemblies in presynaptic terminals. Similarly, clusters of postsynaptic receptors and F-actin are visible in GABAergic dendrites prior to spine outgrowth. Surprisingly, these developmental processes occur without a requirement for synaptic activity. Likewise, the initial stages of spine outgrowth and receptor clustering are not altered by deletion of the C. elegans ortholog of the transsynaptic adhesion protein, neurexin/NRX-1. Over time, however, dendritic spines and postsynaptic receptor clusters are destabilized in the absence of presynaptic NRX-1/neurexin and collapse prior to adulthood. The kinesin-3 family member, UNC-104, delivers NRX-1 to presynaptic terminals and ongoing UNC-104 delivery is required into adulthood for the maintenance of postsynaptic structure. Our findings provide novel insights into the temporal order of synapse formation events in vivo and demonstrate a requirement for transsynaptic adhesion in stabilizing mature circuit connectivity.

The homeodomain transcriptional regulator DVE-1 directs a program for synapse elimination during circuit remodeling

“…Using a previously developed strategy for cellspecific labeling of endogenous LEV-10 [35], we found that mutation of dve-1 also slowed the removal of LEV-10 from the dorsal processes of DD neurons during remodeling. LEV-10 was primarily associated with dorsal processes prior to remodeling and was redistributed to ventral processes during remodeling (Figure 1F Likewise, mutation of dve-1 had little effect on the density of DD dendritic spines that are formed after remodeling (Figure S1.3C, D) [36][37][38]. These findings indicate that the evolutionarily conserved transcription factor DVE-1 specifically governs the elimination of juvenile postsynaptic sites during remodeling without affecting the formation or maturation of new postsynaptic sites.…”

“…L4 animals (40 hours post-hatch) were staged 24 hours prior to experiments on fresh ATR OP50 NGM plates. Imaging was performed with 1-day age adults immobilized in hydrogel [37, 82]. Animals were transferred to 7.5 μL of the hydrogel mix placed on a silanized glass slide and covered with cover slip.…”

“…Similar to juvenile iAChR clusters, dorsal LEV-10 scaffolds in GABAergic neurons of dve-1 mutants were not properly eliminated during remodeling, further demonstrating that DVE-1 coordinates the removal of juvenile postsynaptic sites in DD neurons. Interestingly, mutation of dve-1 did not affect the formation of new ventral postsynaptic sites on DD neurons during remodeling or their abundance (Figure 1E Likewise, mutation of dve-1 had little effect on the density of DD dendritic spines that are formed after remodeling (Figure S1.3C, D) [36][37][38]. These findings indicate that the evolutionarily conserved transcription factor DVE-1 specifically governs the elimination of juvenile postsynaptic sites during remodeling without affecting the formation or maturation of new postsynaptic sites.…”

“…Unless noted otherwise, all strains were immobilized with sodium azide (0.3M) on a 2% or 5% agarose pad. All confocal Images were obtained either using an Olympus BX51WI spinning disk confocal equipped with a 63x objective or on the Yokogawa CSU-X1-A1N spinning disk confocal system (Perkin Elmer) equipped with EM-CCD camera (Hamamatsu, C9100-50) and 63x oil Spine/dendrite analysis: Spine number was quantified as described previously [37,38]. Briefly, spines were counted within a 30 µm ROI anterior to the soma of DD1.…”

“…The copyright holder for this preprint this version posted October 21, 2022. ; https://doi.org/10.1101/2022.10.21.512874 doi: bioRxiv preprint with 1-day age adults immobilized in hydrogel [37,82]. Animals were transferred to 7.5 μL of the hydrogel mix placed on a silanized glass slide and covered with cover slip.…”