A Conserved Tyrosine Residue in Slitrk3 Carboxyl-Terminus Is Critical for GABAergic Synapse Development

Jun Li,Qun Liu,Kunwei Wu,Wei Lu,Yuping Derek Li,Wenyan Han

doi:10.3389/fnmol.2019.00213

Abstract

Single-passing transmembrane protein, Slitrk3 (Slit and Trk-like family member 3, ST3), is a synaptic cell adhesion molecule highly expressed at inhibitory synapses. Recent studies have shown that ST3, through its extracellular domain, selectively regulates inhibitory synapse development via the trans-synaptic interaction with presynaptic cell adhesion molecule, receptor protein tyrosine phosphatase δ (PTPδ) and the cis-interaction with postsynaptic cell adhesion molecule, Neuroligin 2 (NL2). However, little is known about the physiological function of ST3 intracellular, carboxyl (C)-terminal region. Here we report that in heterologous cells, ST3 C-terminus is not required for ST3 homo-dimerization and trafficking to the cell surface. In contrast, in hippocampal neurons, ST3 C-terminus, more specifically, the conserved tyrosine Y969 (in mice), is critical for GABAergic synapse development. Indeed, overexpression of ST3 Y969A mutant markedly reduced the gephyrin puncta density and GABAergic transmission in hippocampal neurons. In addition, single-cell genetic deletion of ST3 strongly impaired GABAergic transmission. Importantly, wild-type (WT) ST3, but not the ST3 Y969A mutant, could fully rescue GABAergic transmission deficits in neurons lacking endogenous ST3, confirming a critical role of Y969 in the regulation of inhibitory synapses. Taken together, our data identify a single critical residue in ST3 C-terminus that is important for GABAergic synapse development and function.

Highlights

Synapses, the highly specialized cellular junctions, are essential for rapid chemical communication between neurons
We first examined whether ST3 could form homo-dimers in heterologous cells and whether ST3 C-terminus was important in this process, as dimerization is a common feature for transmembrane protein-mediated signaling (Maruyama, 2015) and is important for cell adhesion molecules in promoting synapse development and function (Ko et al, 2009; Fogel et al, 2011; Shipman and Nicoll, 2012)
We found that ST3 Y969ARes could not rescue inhibitory transmission in neurons expressing single-guidance RNA (sgRNA)#2 (Figure 5F), consistent with the cell biological data of gephyrin puncta density (Figure 5E)

Summary

Introduction

The highly specialized cellular junctions, are essential for rapid chemical communication between neurons. Glutamate is the predominant excitatory neurotransmitter in the central nervous system and mainly acts on ionotropic glutamate receptors to mediate excitatory transmission. GABA is the dominant inhibitory neurotransmitter in the adult brain and fast inhibitory transmission is largely mediated by GABAA receptors, a process that provides inhibitory balance to glutamatergic excitation and controls neuronal output. Slitrk Y969 Controls GABAergic Synaptogenesis critical to understand the molecular mechanisms for synaptogenesis and synaptic function. While development of glutamatergic synapses has been extensively studied (Waites et al, 2005; McAllister, 2007; Kelsch et al, 2010; Clarke and Barres, 2013; Hanse et al, 2013), much less is known about the mechanisms underlying GABAergic synapse development

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Conclusion