Biology subjects

Sleigh, J. N.

Publications and source records attributed to Sleigh, J. N..

At least 19 recordsLinked to original sources

bioRxiv2026

The neuropathy-causing GARS1{triangleup}ETAQ mutation drives pathology in subsets of motor and sensory neurons in mice

Charcot-Marie-Tooth disease type 2D (CMT2D) results from gain-of-function mutations in GARS1, which encodes glycyl-tRNA synthetase (GlyRS), the enzyme responsible for charging transfer RNA (tRNA) with glycine. There are several CMT2D mouse models, but Gars{Delta}ETAQ/+ is the only one that bears a patient-sourced mutation. Created using CRISPR/Cas9 to model a 12-nucleotide de novo GARS1 deletion identified in an unusually severe CMT2D patient, Gars{Delta}ETAQ/+ mice have previously been shown to display several neuromuscular phenotypes; motor axon loss, denervated neuromuscular junctions (NMJs) and reduced muscle function. Here, we extend these analyses to provide a more comprehensive understanding of both motor and sensory nerve deficits across hind- and fore-limbs. At 3 months, Gars{Delta}ETAQ/+ mice possess sex-independent alterations in the levels of neuropathy biomarkers - including decreased NfL and increased periaxin - alongside reduced muscle endurance and strength, and impairments in the sensory modalities of mechanosensation, proprioception and nociception. Underpinning these dysfunctions, we identified site-specific defects comprising altered sensory neuron populations, muscle spindle loss, reduced motor neuron size, disrupted NMJ innervation and maturation, and reduced axonal transport of signalling endosomes in vivo. Together, these experiments show that Gars{Delta}ETAQ/+ mice display robust and selective peripheral nerve pathology that manifests in a general distal-to-proximal fashion, priming this CMT2D allele for testing treatments and evaluating mechanisms underlying peripheral nerve vulnerability. O_FIG O_LINKSMALLFIG WIDTH=200 HEIGHT=200 SRC="FIGDIR/small/736541v1_ufig1.gif" ALT="Figure 1"> View larger version (70K): org.highwire.dtl.DTLVardef@b48a41org.highwire.dtl.DTLVardef@e0c22dorg.highwire.dtl.DTLVardef@1ec2f5forg.highwire.dtl.DTLVardef@11a3311_HPS_FORMAT_FIGEXP M_FIG C_FIG

neuroscience↗

bioRxiv2026

Sex-Dimorphic Neural Memory Shapes Pancreatic Tissue Resilience

Epithelial cells can encode prior damage into lasting epigenetic and functional states, enabling a primed response to future insults. In the pancreas, acute injury induces reversible acinar cell reprogramming toward a progenitor-like identity that persists beyond repair, supporting resilience to recurrent injury but creating a permissive state for malignant transformation. Given the central role of the tissue niche in stem cell regulation, we investigated microenvironmental adaptations that sustain this primed epithelial state. Using genetic mouse models and ex vivo organoid co-cultures, we identify a sex-specific sensory neural memory after pancreatitis that sustains long-term epithelial plasticity through a CGRP-dependent neuron-epithelial axis. We show that sex differences in acute inflammation drive neutrophil-dependent suppression of neural activation in females, decoupling neural memory from epithelial plasticity after repair. In males, neural memory promotes post-injury plasticity, revealing tissue memory as coordinated adaptation between epithelial progenitors and their niche.

cancer biology↗

bioRxiv2025

CANVAS causing AAGGG repeat expansions cause tissue-specific reduction in RFC1 expression and increase sensitivity to DNA damage

Biallelic AAGGG expansions in Replication Factor Complex Subunit 1 (RFC1) are associated with cerebellar ataxia, neuropathy, vestibular areflexia syndrome (CANVAS) and are increasingly recognised as a common cause of adult-onset ataxia and sensory neuropathy. However, the disease-causing mechanisms remain unclear. Here we leveraged in vitro assays, post-mortem brain tissue, patient-derived cell lines and a neuronal Drosophila model to demonstrate that AAGGG expansions are associated with tissue-specific reductions in the expression of RFC1 transcript, along with impaired RFC1 function and increased sensitivity to DNA damage from platinum-based drugs. CRISPR/Cas9 excision of the AAGGG repeat and flanking AluSx3 element normalized RFC1 expression in iPSC-derived neurons and rescued the DNA damage response, providing a framework for future therapeutic strategies. We also show that these biological findings are clinically relevant in heterozygous AAGGG expansion carriers, who display an increased risk and severity of neuropathy with platinum-based chemotherapy.

neuroscience↗

bioRxiv2025

CNTF specifically slows down the axonal transport of signalling endosomes

Efficient axonal transport is essential for maintaining neuronal function, enabling the bidirectional delivery of diverse cargoes between the cell body and distal compartments. In the neuromuscular system, neurotrophic factors (NTFs) regulate motor neuron survival, function, and synaptic connectivity, in part, through retrograde trafficking of activated NTF-receptor complexes from the neuromuscular junction (NMJ) to the cell body. We recently demonstrated that brain-derived neurotrophic factor (BDNF) stimulation to muscles selectively enhances retrograde transport of signalling endosomes in fast, but not slow, motor neurons in vivo. Moreover, both axonal endosome transport and its BDNF-mediated regulation are disrupted in mouse models of diseases impacting motor neurons. Here, we examined whether additional NTFs, when applied to distal axon terminals, share this transport-modulating property. Through imaging sciatic nerves in anaesthetised mice, we tracked the in vivo dynamics of signalling endosomes in fast (FMN) and slow motor neurons (SMN) via intramuscular injections of a fluorescently conjugated, atoxic fragment of tetanus neurotoxin (HCT). HCT was co-administered with ciliary neurotrophic factor (CNTF), hepatocyte growth factor (HGF), neurturin (NRTN), or proBDNF - four growth factors with known effects on motor neurons. Compared to vehicle-treated controls, proBDNF, HGF, and NRTN, produced no detectable change in transport dynamics. In contrast, CNTF markedly reduced endosome speeds in both FMNs and SMNs, indicating remarkable selectivity of specific NTFs in the regulation of signalling endosome transport in motor neurons. Understanding this selectivity may aid the development of muscle-targeted NTF-based therapeutic strategies aimed at restoring axonal transport in neurodegenerative disease, peripheral neuropathy, and nerve injury. Graphical Abstract O_FIG O_LINKSMALLFIG WIDTH=200 HEIGHT=88 SRC="FIGDIR/small/681259v1_ufig1.gif" ALT="Figure 1"> View larger version (28K): org.highwire.dtl.DTLVardef@10e4229org.highwire.dtl.DTLVardef@119c69aorg.highwire.dtl.DTLVardef@13dd629org.highwire.dtl.DTLVardef@b733ec_HPS_FORMAT_FIGEXP M_FIG C_FIG

neuroscience↗

bioRxiv2025

TBK1 activity regulates the directionality of axonal transport of signalling endosomes

The polarised and complex morphology of neurons pose massive challenges for efficient cargo delivery between the axon and soma, a process termed axonal transport. We have previously shown that the retrograde axonal transport of pro-survival, neurotrophic signalling endosomes relies on Rab7 in motor neurons, and that their trafficking is impaired in the early stages of amyotrophic lateral sclerosis (ALS) pathogenesis. Here, we report the effect of Rab7 phosphorylation on the transport of these signalling endosomes. We show that the ALS-linked kinase TBK1 phosphorylates Rab7 at S72 in neurons, altering its binding to cytoplasmic dynein adaptors. Accordingly, both TBK1 knockdown and the expression of a loss-of-function Rab7 mutant (S72E) induce aberrant bidirectional movement of signalling endosomes without modifying neuronal polarity or endosomal sorting. This alteration is specific for signalling endosomes, as axonal transport of lysosomes and mitochondria remain unaffected. We have therefore discovered a new TBK1 function that ensures the unidirectional transport of signalling endosomes, suggesting that reduced TBK1 activity determines retrograde transport dysfunctions and long-range signalling impairments. SummarySignalling endosomes travel from the distal axon to the cell body, exerting pro-survival functions. TBK1, an ALS-linked kinase, governs the directionality of signalling endosome transport in motor neurons by phosphorylating Rab7. Thus, loss of TBK1 function results in long-range signalling impairment.

neuroscience↗

bioRxiv2025

Innervation and cargo-specific axonal transport impairments in FUS-ALS mice with gain and loss of function

Mutations in the RNA-binding protein FUS lead to nuclear depletion and cytoplasmic mislocalisation of the protein and cause amyotrophic lateral sclerosis (ALS). Using a novel FUS-ALS mouse model, we found that adult mutant mice develop loss of function transcriptomic alterations, along with aberrant cytoplasmic partitioning associated with translatome deficits. Neuromuscular junction innervation was selectively impaired in FUS-ALS females; however, reinnervation following sciatic nerve crush was equally perturbed in both sexes. Additionally, we observed cargo-specific axonal transport alterations, a process critical for neuronal maintenance. In vivo mitochondrial transport was impaired across FUS-ALS mice, whereas the transport of signalling endosomes was selectively disrupted in mutant females. Altogether, our findings identify broader and sex-dependent motor neuron dysfunction in FUS-ALS, emphasise the link between endosomal transport impairments and denervation in disease, and establish FUS-ALS mice as a valuable model for investigating early cellular impairments driving ALS pathology.

neuroscience↗

bioRxiv2025

Processivity and BDNF-dependent modulation of signalling endosome axonal transport are impaired in aged mice

A healthy nervous system is reliant upon an efficient transport network to deliver essential cargoes throughout the extensive and polarised architecture of neurons. The trafficking of cargoes, such as organelles and proteins, is particularly challenging within the long projections of neurons, which, in the case of axons, can be more than four orders of magnitude longer than cell bodies. It is therefore unsurprising that disruptions in axonal transport have been reported across neurological diseases. A decline in this essential process has also been identified in many aging models, perhaps compounding age-related neurodegeneration. Via intravital imaging, we recently determined that, despite a reduction in overall motility, the run speed and displacement of anterograde mitochondrial transport were unexpectedly enhanced in aged mouse peripheral nerves. Here, to determine how aging impacts a different axonal cargo, we evaluated in vivo trafficking of signalling endosomes in motor axons of mouse sciatic nerves from 3 to 22 months. Contrasting with mitochondria, we did not detect alterations in signalling endosome speed, but found a consistent rise in pausing that manifested after 18 months. We then treated muscles with brain-derived neurotrophic factor (BDNF), which regulates axonal transport of signalling endosomes in motor neurons; however, we observed no change in the processivity defect at 22 months, consistent with downregulation of the BDNF receptor TrkB at the neuromuscular junction. Together, these findings indicate that aging negatively impacts signalling endosome trafficking in motor axons likely through dampened BDNF signalling at the motor neuron-muscle interface. Graphical Abstract O_FIG O_LINKSMALLFIG WIDTH=200 HEIGHT=195 SRC="FIGDIR/small/635507v1_ufig1.gif" ALT="Figure 1"> View larger version (84K): org.highwire.dtl.DTLVardef@d5fe63org.highwire.dtl.DTLVardef@13033c2org.highwire.dtl.DTLVardef@19621dcorg.highwire.dtl.DTLVardef@189121a_HPS_FORMAT_FIGEXP M_FIG C_FIG

neuroscience↗

bioRxiv2024

Refining gene delivery to skeletal muscle with a dual-strategy approach of muscle-tropic AAV capsids and muscle-specific promoters.

Viral vector technologies based on adeno-associated virus (AAV) have demonstrated promising ability to deliver genetic cargo to a range of organs in vivo, with several novel candidates showing clinical efficacy in human trials over the past decade. However, naturally occurring AAV serotypes are limited in their ability to target skeletal muscle, an important gene therapy target for many neuromuscular disorders. This means that high doses of AAV are often required to achieve therapeutically effective doses in muscle. To overcome this, novel AAV vector capsids have been engineered by inserting targeting peptides into the AAV9 capsid variable region VIII (VRIII) to achieve greater muscle transduction efficiency. Here we describe investigation of a newly reported capsid, called MyoAAV1A combined with clinically validated muscle-specific promoters. We profiled the efficiency of in vivo delivery to murine skeletal muscle and found that the optimal combination of MyoAAV1A capsid with MHCK7 promoter maintains transgene expression in skeletal muscle, and reduces expression in off-target tissues, particularly the liver. This highlights a promising capsid-promoter combination to progress in further preclinical research for skeletal muscle gene therapy. Graphical abstract O_FIG O_LINKSMALLFIG WIDTH=200 HEIGHT=143 SRC="FIGDIR/small/605568v1_ufig1.gif" ALT="Figure 1"> View larger version (29K): org.highwire.dtl.DTLVardef@10bbe78org.highwire.dtl.DTLVardef@5e2e0org.highwire.dtl.DTLVardef@71f4a7org.highwire.dtl.DTLVardef@1750d81_HPS_FORMAT_FIGEXP M_FIG C_FIG

bioengineering↗

bioRxiv2024

The node of Ranvier influences the in vivo axonal transport of mitochondria and signalling endosomes

Efficient long-range axonal transport is essential for maintaining neuronal function, and perturbations in this process underlie severe neurological diseases. We have previously demonstrated that signalling endosomes are transported in vivo at comparable speeds across motor neurons (MNs) innervating different hindlimb muscles, as well as between forelimb and hindlimb peripheral nerves. In contrast, axonal transport is faster in MNs compared to sensory neurons innervating the same muscle. Found periodically across the myelin sheath, Nodes of Ranvier (NoR) are short uncovered axonal domains that facilitate action potential propagation. Currently, it remains unresolved how the distinct molecular structures of the NoR impact axonal transport dynamics. Here, using intravital time-lapse microscopy of sciatic nerves in live, anaesthetised mice, we assessed diverse organelle dynamics at the NoR. We first observed that axonal morphologies were similar between fast and slow MNs, and found that signalling endosomes and mitochondria accumulate on the distal side of the NoR in both motor neuron subtypes. Assessment of axonal transport of signalling endosomes and mitochondria revealed a decrease in velocity and increase in pausing as the organelles transit through the NoR, followed by an increase in speed in the adjacent intranodal region. Collectively, this study has established axonal transport dynamics of two independent organelles at the NoR in vivo, and has relevance for several pathologies affecting peripheral nerves and the NoR, such as peripheral neuropathy, motor neuron diseases, and/or multiple sclerosis.

neuroscience↗

bioRxiv2023

BDNF controls phosphorylation and transcriptional networks governing cytoskeleton organization and axonal regeneration

The cell-intrinsic capacity of neurons to regenerate axons requires widespread coordination of the transcriptome, activation of multiple kinases, and reorganization of the cytoskeleton. Axonal repair is also influenced by extrinsic activating factors, such as neurotrophins. Here, we reveal that brain-derived neurotrophic factor (BDNF) amplifies multiple neuron-intrinsic programs to foster axonal regeneration in human motor neurons. Through metabolic RNA sequencing and phosphoproteomic profiling, we elucidate BDNF signalling and its role in axonal regeneration. We discover that BDNF controls RNA stability and transcriptional programs that converge with regeneration-associated gene (RAG) sets. We further unveil that BDNF governs the phosphorylation of multiple proteins essential for cytoskeletal dynamics, a major determinant of effective nerve regeneration. Using compartmentalized neuronal cultures, we demonstrate that the regeneration driven by BDNF depends on the axon-specific activation of ERK/RSK/S6K kinase pathway. We propose a model in which BDNF augments neuron-intrinsic pathways to drive axonal regeneration in human motor neurons. TeaserBDNF aids nerve repair by fine-tuning the metabolism of RNA and by changing the building blocks of the nerve cell cytoskeleton.

molecular biology↗

bioRxiv2023

Age-specific and compartment-dependent changes in mitochondrial homeostasis and cytoplasmic viscosity in mouse peripheral neurons

Mitochondria are dynamic bioenergetic hubs that become compromised with age. In neurons, declining mitochondrial axonal transport has been associated with reduced cellular health. However, it is still unclear to what extent the decline of mitochondrial transport and function observed during ageing are coupled, and if somal and axonal mitochondria display compartment-specific features that make them more susceptible to the ageing process. It is also not known whether the biophysical state of the cytoplasm, thought to affect many cellular functions, changes with age to impact mitochondrial trafficking and homeostasis. Focusing on the mouse peripheral nervous system, we show that age-dependent decline in mitochondrial trafficking is accompanied by reduction of mitochondrial membrane potential and intra-mitochondrial viscosity, but not calcium buffering, in both somal and axonal mitochondria. Intriguingly, we observe a specific increase in cytoplasmic viscosity in the neuronal cell body, where mitochondria are most polarised, which correlates with decreased cytoplasmic diffusiveness. Increasing cytoplasmic crowding in the somatic compartment of DRG neurons grown in microfluidic chambers reduces mitochondrial axonal trafficking, suggesting a mechanistic link between the regulation of cytoplasmic viscosity and mitochondrial dynamics. Our work provides a reference for studying the relationship between neuronal mitochondrial homeostasis and the viscoelasticity of the cytoplasm in a compartment-dependent manner during ageing.

neuroscience↗

bioRxiv2023

Boosting BDNF in muscle rescues impaired in vivo axonal transport in a mouse model of DI-CMTC peripheral neuropathy

Charcot-Marie-Tooth disease (CMT) is a genetic peripheral neuropathy caused by mutations in many functionally diverse genes. The aminoacyl-tRNA synthetase (ARS) enzymes, which transfer amino acids to partner tRNAs for protein synthesis, represent the largest protein family genetically linked to CMT aetiology, suggesting pathomechanistic commonalities. Dominant intermediate CMT type C (DI-CMTC) is caused by YARS1 mutations driving a toxic gain-of-function in the encoded tyrosyl-tRNA synthetase (TyrRS), which is mediated by exposure of consensus neomorphic surfaces through conformational changes of the mutant protein. In this study, we first showed that human DI-CMTC-causing TyrRSE196K mis-interacts with the extracellular domain of the BDNF receptor TrkB, an aberrant association we have previously characterised for several mutant glycyl-tRNA synthetases linked to CMT type 2D (CMT2D). We then performed temporal neuromuscular assessments of YarsE196K mice modelling DI-CMT. We determined that YarsE196K homozygotes display a selective, age-dependent impairment in in vivo axonal transport of neurotrophin-containing signalling endosomes, phenocopying CMT2D mice. This impairment is replicated by injection of recombinant TyrRSE196K, but not TyrRSWT, into muscles of wild-type mice. Augmenting BDNF in DI-CMTC muscles, through injection of recombinant protein or muscle-specific gene therapy, resulted in complete axonal transport correction. Therefore, this work identifies a non-cell autonomous pathomechanism common to ARS-related neuropathies, and highlights the potential of boosting BDNF levels in muscles as a therapeutic strategy.

neuroscience↗

bioRxiv2021

BDNF-dependent modulation of axonal transport is selectively impaired in ALS

Axonal transport ensures long-range delivery of essential cargoes between proximal and distal compartments of neurons, and is needed for neuronal development, function, and survival. Deficits in axonal transport have been detected at pre-symptomatic stages in mouse models of amyotrophic lateral sclerosis (ALS), suggesting that impairments are fundamental for disease pathogenesis. However, the precise mechanisms responsible for the transport deficits and whether they preferentially affect -motor neuron (MN) subtypes remain unresolved. Here, we report that stimulation of wild-type neurons with brain-derived neurotrophic factor (BDNF) enhances trafficking of signalling endosomes specifically in fast MNs (FMNs). In early symptomatic SOD1G93A mice, FMNs display selective impairment of axonal transport and develop an insensitivity to BDNF stimulation, with pathology upregulating classical non-pro-survival receptors in muscles and sciatic nerves. Altogether, these data indicate that cell- and non-cell autonomous BDNF signalling is impaired in vulnerable SOD1G93A MNs, thus identifying a new key deficit in ALS amenable for future therapeutic interventions.

neuroscience↗

bioRxiv2020

NMJ-Analyser: high-throughput morphological screening of neuromuscular junctions identifies subtle changes in mouse neuromuscular disease models

The neuromuscular junction (NMJ) is the peripheral synapse formed between a motor neuron axon terminal and a muscle fibre. NMJs are thought to be the primary site of peripheral pathology in many neuromuscular diseases, but innervation/denervation status is often assessed qualitatively with poor systematic criteria across studies, and separately from 3D morphological structure. Here, we describe the development of NMJ-Analyser, to comprehensively screen the morphology of NMJs and their corresponding innervation status automatically. NMJ-Analyser generates 29 biologically relevant features to quantitatively define healthy and aberrant neuromuscular synapses and applies machine learning to diagnose NMJ degeneration. We validated this framework in longitudinal analyses of wildtype mice, as well as in four different neuromuscular disease models: three for amyotrophic lateral sclerosis (ALS) and one for peripheral neuropathy. We showed that structural changes at the NMJ initially occur in the nerve terminal of mutant TDP43 and FUS ALS models. Using a machine learning algorithm, healthy and aberrant neuromuscular synapses are identified with 95% accuracy, with 88% sensitivity and 97% specificity. Our results validate NMJ-Analyser as a robust platform for systematic and structural screening of NMJs, and pave the way for transferrable, and cross-comparison and high-throughput studies in neuromuscular diseases.

neuroscience↗

bioRxiv2020

Developmental demands contribute to early neuromuscular degeneration in CMT2D mice

Dominantly inherited, missense mutations in the widely expressed housekeeping gene, GARS1, cause Charcot-Marie-Tooth type 2D (CMT2D), a peripheral neuropathy characterised by muscle weakness and wasting in limb extremities. Mice modelling CMT2D display early and selective neuromuscular junction (NMJ) pathology, epitomised by disturbed maturation and neurotransmission, leading to denervation. Indeed, the NMJ disruption has been reported in several different muscles; however, a systematic comparison of neuromuscular synapses from distinct body locations has yet to be performed. We therefore analysed NMJ development and degeneration across five different wholemount muscles to identify key synaptic features contributing to the distinct pattern of neurodegeneration in CMT2D mice. Denervation was found to occur along a distal-to-proximal gradient, providing a cellular explanation for the greater weakness observed in mutant Gars hindlimbs compared to forelimbs. Nonetheless, muscles from similar locations and innervated by axons of equivalent length showed significant differences in neuropathology, suggestive of additional factors impacting on site-specific neuromuscular degeneration. Defective NMJ development preceded and associated with degeneration, but was not linked to a delay of wild-type NMJ maturation processes. Correlation analyses indicate that muscle fibre type nor synaptic architecture explain the differential denervation of CMT2D NMJs, rather it is the extent of post-natal synaptic growth that predisposes to neurodegeneration. Together, this work improves our understanding of the mechanisms driving synaptic vulnerability in CMT2D and hints at pertinent pathogenic pathways.

neuroscience↗

bioRxiv2020

Altered sensory neuron development in CMT2D mice is site-specific and linked to increased GlyRS levels

Dominant, missense mutations in the widely and constitutively expressed GARS1 gene cause a peripheral neuropathy that usually begins in adolescence and principally impacts the upper limbs. Caused by a toxic gain-of-function in the encoded glycyl-tRNA synthetase (GlyRS) enzyme, the neuropathology appears to be independent of the canonical role of GlyRS in aminoacylation. Patients display progressive, life-long weakness and wasting of muscles in hands followed by feet, with frequently associated deficits in sensation. When dysfunction is observed in motor and sensory nerves, there is a diagnosis of Charcot-Marie-Tooth disease type 2D (CMT2D), or distal hereditary motor neuropathy type V if the symptoms are purely motor. The cause of this varied sensory involvement remains unresolved, as are the pathomechanisms underlying the selective neurodegeneration characteristic of the disease. We have previously identified in CMT2D mice that neuropathy-causing Gars mutations perturb sensory neuron fate and permit mutant GlyRS to aberrantly interact with neurotrophin receptors (Trks). Here, we extend this work by interrogating further the anatomy and function of the CMT2D sensory nervous system in mutant Gars mice, obtaining several key results: 1) sensory pathology is restricted to neurons innervating the hindlimbs; 2) perturbation of sensory development is not common in mouse models of neuromuscular disease; 3) in vitro axonal transport of signalling endosomes is not impaired in afferent neurons of all CMT2D mouse models; and 4) Gars expression is selectively elevated in a subset of sensory neurons and linked to sensory developmental defects. These findings highlight the importance of comparative neurological assessment in mouse models of disease and shed light on key proposed neuropathogenic mechanisms in GARS1-linked neuropathy.

neuroscience↗

bioRxiv2020

Post-synaptic morphology of mouse neuromuscular junctions is linked to muscle fibre type

The neuromuscular junction (NMJ) is the highly specialised peripheral synapse formed between lower motor neuron terminals and muscle fibres. Post-synaptic acetylcholine receptors (AChRs), which are found in high density in the muscle membrane, bind to acetylcholine released into the synaptic cleft of the NMJ, ultimately facilitating the conversion of motor action potentials to muscle contractions. NMJs have been studied for many years as a general model for synapse formation, development and function, and are known to be early sites of pathological changes in many neuromuscular diseases. However, information is limited on the diversity of NMJs in different muscles, whether muscle fibre type impacts NMJ morphology and growth, and the relevance of these parameters to neuropathology. Here, this crucial gap was addressed using a robust and standardised semi-automated workflow called NMJ-morph to quantify features of pre- and post-synaptic NMJ architecture in an unbiased manner. Five wholemount muscles from wild-type mice were dissected and compared at immature (post-natal day, P7) and early adult (P31-32) timepoints. Post-synaptic AChR morphology was found to be more variable between muscles than that of the motor neuron terminal and there were greater differences in the developing NMJ than at the mature synapse. Post-synaptic architecture, but not neuronal morphology or post-natal synapse growth, correlates with fibre type and is largely independent of muscle fibre diameter. Counter to previous observations, this study indicates that smaller NMJs tend to innervate muscles with higher proportions of fast twitch fibres and that NMJ growth rate is not conserved across all muscles. Furthermore, healthy pre- and post-synaptic NMJ morphological parameters were collected for five anatomically and functionally distinct mouse muscles, generating reference data that will be useful for the future assessment of neuromuscular disease models. Graphical Abstract O_FIG O_LINKSMALLFIG WIDTH=198 HEIGHT=200 SRC="FIGDIR/small/025106v1_ufig1.gif" ALT="Figure 1"> View larger version (56K): org.highwire.dtl.DTLVardef@1e87c95org.highwire.dtl.DTLVardef@4b2eaborg.highwire.dtl.DTLVardef@1e4e4e8org.highwire.dtl.DTLVardef@705803_HPS_FORMAT_FIGEXP M_FIG C_FIG

neuroscience↗

bioRxiv2019

Loss of BICD2 in muscle drives motor neuron loss in a developmental form of spinal muscular atrophy

BICD2 is a key component of the dynein/dynactin motor complex. Autosomal dominant mutations in BICD2 cause Spinal Muscular Atrophy Lower Extremity Predominant 2 (SMALED2), a developmental disease of motor neurons. In this study we sought to examine the motor neuron phenotype of conditional Bicd2-/- mice. Bicd2-/- mice show a significant reduction in the number of motor axons of the L4 ventral root compared to wild type mice. Muscle-specific knockout of Bicd2, but not motor neuron-specific Bicd2 loss, results in a reduction in L4 ventral axons comparable to global Bicd2-/- mice. Rab6, a small GTPase required for the sorting of secretory vesicles from the TGN to the plasma membrane is a major binding partner of BICD2. We therefore examined the secretory pathway in SMALED2 patient fibroblasts and demonstrated impaired flow of constitutive secretory cargoes. Together, these data indicate that BICD2 loss from muscles is a major driver of non-cell autonomous pathology with important implications for future therapeutic approaches to SMALED2. SummaryMissense mutations in the cargo adaptor protein BICD2 cause SMALED2, a developmental disease of motor neurons. In this study, the authors show that BICD2 mutations cause motor neuron loss by a non-cell autonomous mechanism determining a disabling impairment of muscle function.

neuroscience↗