Interaction of Axonal Chondrolectin with Collagen XIXa1 Is Necessary for Precise Neuromuscular Junction Formation

Ana-Maria Oprişoreanu,Catherina G Becker,Sukrat Arya,Marcos J Cardozo,Daniel Wehner,Thomas Becker,Kevin Talbot,Zhisheng Zhong ,Hannah Smith ,Richard Webster

doi:10.2139/ssrn.3391947

Ana-Maria Oprişoreanu, Catherina G Becker + Show 8 more

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https://doi.org/10.2139/ssrn.3391947

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Abstract

Chondrolectin (Chodl) is needed for motor axon extension in zebrafish and is dysregulated in mouse models of spinal muscular atrophy (SMA). However, the mechanistic basis of Chodl function is not known. Here, we use Chodl deficient zebrafish and mouse mutants to show that the absence of Chodl leads to anatomical and functional defects of the neuromuscular synapse. In zebrafish, growth of an identified motor axon beyond an “en passant” synapse and later axon branching from synaptic points is impaired, leading to functional deficits. Mechanistically, motor neuron-autonomous Chodl function depends on the presence of intracellular phosphorylation sites and on binding muscle-derived Collagen XIXa1 via its extracellular C-type lectin domain. Our data support evolutionarily conserved roles of Chodl in synaptogenesis and provide evidence for a “synapse-first” scenario of motor axon growth in zebrafish.

Highlights

In zebrafish, three primary motor axons grow out on a common mid-segmental pathway to the horizontal myoseptum, where axons pause and only the axon of the caudal primary motor neuron (CaP) continues its ventral growth (Beattie et al, 2002; Myers et al, 1986; Westerfield et al, 1986)
Motor-neuron-autonomous Chodl function depends on its intracellular domain and on binding muscle-derived collagen XIXa1 by its extracellular C-type lectin domain
Generation of a Zebrafish chodl Mutant For mutagenesis, we used CRISPR technology on the background of a transgenic reporter line in which GFP is expressed under the regulatory sequences of the mnx1 gene to visualize motor neurons (Flanagan-Steet et al, 2005)

Summary

Introduction

Three primary motor axons grow out on a common mid-segmental pathway to the horizontal myoseptum, where axons pause and only the axon of the caudal primary motor neuron (CaP) continues its ventral growth (Beattie et al, 2002; Myers et al, 1986; Westerfield et al, 1986). Growth of new axon branches originates from and depends on synaptic points, e.g., in Xenopus motor axon arborization (Javaherian and Cline, 2005), arborization of retinal ganglion cell axons in zebrafish (Meyer and Smith, 2006), or the thalamo-cortical projection in mammals (Matsumoto et al, 2016). Both CaP axon extension beyond an en passant synapse and axon branching could depend on synapse stabilization in zebrafish, whereas in mammals, motor axon growth mostly precedes terminal synaptogenesis (Sanes and Lichtman, 1999)

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