An Autism-Associated Neuroligin-3 Mutation Affects Developmental Synapse Elimination in the Cerebellum.

Esther Suk King Lai,Taisuke Miyazaki,Takanobu Nakazawa,Masahiko Watanabe,Kouichi Hashimoto,Hisako Nakayama,Masanobu Kano,Katsuhiko Tabuchi

doi:10.3389/fncir.2021.676891

Abstract

Neuroligin is a postsynaptic cell-adhesion molecule that is involved in synapse formation and maturation by interacting with presynaptic neurexin. Mutations in neuroligin genes, including the arginine to cystein substitution at the 451st amino acid residue (R451C) of neuroligin-3 (NLGN3), have been identified in patients with autism spectrum disorder (ASD). Functional magnetic resonance imaging and examination of post-mortem brain in ASD patients implicate alteration of cerebellar morphology and Purkinje cell (PC) loss. In the present study, we examined possible association between the R451C mutation in NLGN3 and synaptic development and function in the mouse cerebellum. In NLGN3-R451C mutant mice, the expression of NLGN3 protein in the cerebellum was reduced to about 10% of the level of wild-type mice. Elimination of redundant climbing fiber (CF) to PC synapses was impaired from postnatal day 10–15 (P10–15) in NLGN3-R451C mutant mice, but majority of PCs became mono-innervated as in wild-type mice after P16. In NLGN3-R451C mutant mice, selective strengthening of a single CF relative to the other CFs in each PC was impaired from P16, which persisted into juvenile stage. Furthermore, the inhibition to excitation (I/E) balance of synaptic inputs to PCs was elevated, and calcium transients in the soma induced by strong and weak CF inputs were reduced in NLGN3-R451C mutant mice. These results suggest that a single point mutation in NLGN3 significantly influences the synapse development and refinement in cerebellar circuitry, which might be related to the pathogenesis of ASD.

Highlights

Establishment of proper neural circuits relies on dynamic processes of synapse formation and elimination/pruning
We examined whether the selective strengthening of a single climbing fiber (CF) among multiple CFs in each Purkinje cell (PC) was affected in NLGN3-R451C mutant mice
We show that an autism-associated genetic mutation of NLGN3 affects developmental synaptic refinement in the mouse cerebellum

Summary

Introduction

Establishment of proper neural circuits relies on dynamic processes of synapse formation and elimination/pruning. During postnatal development, some synapses are strengthened, whereas others are weakened and eventually eliminated in a neural activity-dependent manner (Purves and Lichtman, 1980; Lichtman and Colman, 2000; Hua and Smith, 2004; Kano and Hashimoto, 2009). Accumulating evidence strongly suggests that abnormality in developmental synapse elimination underlies the pathophysiology of neurodevelopmental and psychiatric disorders including autism spectrum disorder (ASD) (Zoghbi, 2003; Penzes et al, 2011). ASD is highly hereditary, numerous ASD-associated genes have been identified, and a number of ASD mouse models have been reported (Abrahams and Geschwind, 2008; Bourgeron et al, 2009; Tsai et al, 2012a). Majority of ASD-associated genes are thought to encode synaptic proteins such as synaptic cell adhesion molecules, neuroligin and neurexin families (Südhof, 2008; Singh and Eroglu, 2013; Mackowiak et al, 2014; Stewart, 2015) and a scaffold protein in the postsynaptic density, SHANK/ProSAP (Berkel et al, 2010; Arons et al, 2012; Guilmatre et al, 2014)

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