Postsynaptic CaV1.1-driven calcium signaling coordinates presynaptic differentiation at the developing neuromuscular junction

Mehmet Mahsum Kaplan,Bernhard E Flucher

doi:10.1038/s41598-019-54900-w

Mehmet Mahsum Kaplan, Bernhard E Flucher

Open Access

https://doi.org/10.1038/s41598-019-54900-w

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Journal: Scientific Reports	Publication Date: Dec 1, 2019
Citations: 6	License type: open-access

Affiliation: Innsbruck Medical University

Abstract

Proper formation of neuromuscular synapses requires the reciprocal communication between motor neurons and muscle cells. Several anterograde and retrograde signals involved in neuromuscular junction formation are known. However the postsynaptic mechanisms regulating presynaptic differentiation are still incompletely understood. Here we report that the skeletal muscle calcium channel (CaV1.1) is required for motor nerve differentiation and that the mechanism by which CaV1.1 controls presynaptic differentiation utilizes activity-dependent calcium signaling in muscle. In mice lacking CaV1.1 or CaV1.1-driven calcium signaling motor nerves are ectopically located and aberrantly defasciculated. Axons fail to recognize their postsynaptic target structures and synaptic vesicles and active zones fail to correctly accumulate at the nerve terminals opposite AChR clusters. These presynaptic defects are independent of aberrant AChR patterning and more sensitive to deficient calcium signals. Thus, our results identify CaV1.1-driven calcium signaling in muscle as a major regulator coordinating multiple aspects of presynaptic differentiation at the neuromuscular synapse.

Highlights

Proper formation of neuromuscular synapses requires the reciprocal communication between motor neurons and muscle cells
This study focuses on the role of CaV1.1-dependent calcium signaling in regulating the presynaptic motor neuron differentiation during neuromuscular junction (NMJ) formation
By analyzing two distinct mouse models, both of which lack activity-dependent postsynaptic calcium signaling, we report a central role of muscle calcium signals in the regulation of multiple distinct aspects of the presynaptic differentiation at the forming NMJ

Summary

Introduction

Proper formation of neuromuscular synapses requires the reciprocal communication between motor neurons and muscle cells. On the presynaptic side differentiation of the motor axons involves multiple characteristic steps, including the growth and branching pattern of motor nerve fascicles in the center of the muscle, the recognition of the postsynaptic target sites, and the differentiation of the nerve terminals opposite the AChR clusters Each of these steps is regulated by specific retrograde signaling mechanisms originating from the muscle[13]. We demonstrate that the aberrant growth and innervation of the motor axons in the calcium channel mutants is not limited to the extent expected from the wider distribution of their target structures, but include characteristic properties established before and after contacting AChR clusters To dissect these individual aspects of motor nerve differentiation and examine their potential dependence on CaV1.1-driven calcium signals, we analyzed nerve growth patterns, fasciculation, target recognition, and differentiation of nerve terminals in three genetic mouse models. The scope and extent of presynaptic aberrations in these mice indicate a central role of postsynaptic CaV1.1-driven calcium signals in regulating presynaptic differentiation at the developing NMJ

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