Optogenetic control of excitatory post-synaptic differentiation through neuroligin-1 tyrosine phosphorylation.

Mathieu Letellier,Béatrice Tessier,Matthieu Lagardère,Olivier Thoumine,Harald Janovjak

doi:10.7554/elife.52027

Abstract

Neuroligins (Nlgns) are adhesion proteins mediating trans-synaptic contacts in neurons. However, conflicting results around their role in synaptic differentiation arise from the various techniques used to manipulate Nlgn expression level. Orthogonally to these approaches, we triggered here the phosphorylation of endogenous Nlgn1 in CA1 mouse hippocampal neurons using a photoactivatable tyrosine kinase receptor (optoFGFR1). Light stimulation for 24 hr selectively increased dendritic spine density and AMPA-receptor-mediated EPSCs in wild-type neurons, but not in Nlgn1 knock-out neurons or when endogenous Nlgn1 was replaced by a non-phosphorylatable mutant (Y782F). Moreover, light stimulation of optoFGFR1 partially occluded LTP in a Nlgn1-dependent manner. Combined with computer simulations, our data support a model by which Nlgn1 tyrosine phosphorylation promotes the assembly of an excitatory post-synaptic scaffold that captures surface AMPA receptors. This optogenetic strategy highlights the impact of Nlgn1 intracellular signaling in synaptic differentiation and potentiation, while enabling an acute control of these mechanisms.

Highlights

How early neuronal connections mature into functional synapses is a key question in neurobiology, and adhesion molecules such as neuroligins (Nlgs) are thought to play important roles in this process (Bemben et al, 2015; Craig and Kang, 2007; Südhof, 2008)
Orthogonal to the traditional paradigms used to manipulate Nlg expression level or replace Nlg isoforms with truncated or mutated versions, this novel optogenetic approach allows for a fine tuning of the tyrosine phosphorylation of endogenous Nlg1, revealing a strong role of Nlg1 intracellular signaling in excitatory post-synapse differentiation
NMDA receptors (NMDARs)-mediated EPSCs are not affected by Nlg1 phosphorylation, supporting the concept of a direct extracellular coupling between Nlg1 and GluN1 (Budreck et al, 2013; Shipman and Nicoll, 2012)

Summary

Introduction

How early neuronal connections mature into functional synapses is a key question in neurobiology, and adhesion molecules such as neuroligins (Nlgs) are thought to play important roles in this process (Bemben et al, 2015; Craig and Kang, 2007; Südhof, 2008). Whereas Nlg OE or KD bi-directionally affect synapse number, full or conditional Nlg1/2/3 KO does not alter synapse density (Chanda et al, 2017; Chih et al, 2005; Levinson et al, 2005; Prange et al, 2004; Varoqueaux et al, 2006), suggesting that neuroligins are not generally required for synaptogenesis. To address this apparent conflict, experiments that mixed wild type and Nlg KO neurons suggested the interesting model that neurons might compete with one another for synapse formation, depending on their intrinsic Nlg level (Kwon et al, 2012). While it is generally accepted that NMDAR-dependent long-term potentiation (LTP) is impaired by Nlg KD or KO, the issues of which Nlg motifs are important in this process and whether the Nlg1-NMDAR interaction is required, are unclear (Jiang et al, 2017; Kim et al, 2008; Letellier et al, 2018; Shipman and Nicoll, 2012; Wu et al, 2019)

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Results

Conclusion