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Neuron Feb 2019In vertebrates, commissural axons extend ventrally toward the floor plate in the spinal cord and hindbrain. Netrin-1, secreted by floor plate cells, was proposed to...
In vertebrates, commissural axons extend ventrally toward the floor plate in the spinal cord and hindbrain. Netrin-1, secreted by floor plate cells, was proposed to attract commissural axons at a distance. However, recent genetic studies in mice have shown that netrin-1 is also produced by ventricular zone (VZ) progenitors and that in the hindbrain, it represents the main source of netrin-1 for commissural axons. Here, we show that genetically deleting netrin-1 either from the VZ or the floor plate does not prevent midline crossing in the spinal cord, although axon pathfinding and fasciculation are perturbed. Strikingly, the VZ and floor plate act synergistically, as the simultaneous ablation of netrin-1 from these two sources severely impedes crossing. These results suggest that floor-plate-derived netrin-1 has a distinct impact on commissural axons in the spinal cord and hindbrain.
Topics: Animals; Axon Guidance; Cerebral Ventricles; Female; Male; Mice; Netrin-1; Neurons; Rhombencephalon; Spinal Cord
PubMed: 30661739
DOI: 10.1016/j.neuron.2018.12.024 -
International Journal of Molecular... Dec 2019The G protein-coupled cannabinoid receptors type 1 (CB1R) and type 2 (CB2R), and their endocannabinoid (eCBs) ligands, have been implicated in several aspects of brain...
The G protein-coupled cannabinoid receptors type 1 (CB1R) and type 2 (CB2R), and their endocannabinoid (eCBs) ligands, have been implicated in several aspects of brain wiring during development. Here we aim to assess whether interfering with CB1R affects development, neuritogenesis and pathfinding of GnRH and AgRP neurons, forebrain neurons that control respectively reproduction and appetite. We pharmacologically and genetically interfered with CB1R in zebrafish strains with fluorescently labeled GnRH3 and the AgRP1 neurons. By applying CB1R antagonists we observed a reduced number of GnRH3 neurons, fiber misrouting and altered fasciculation. Similar phenotypes were observed by CB1R knockdown. Interfering with CB1R also resulted in a reduced number, misrouting and poor fasciculation of the AgRP1 neuron's axonal projections. Using a bioinformatic approach followed by qPCR validation, we have attempted to link CB1R functions with known guidance and fasciculation proteins. The search identified stathmin-2, a protein controlling microtubule dynamics, previously demonstrated to be coexpressed with CB1R and now shown to be downregulated upon interference with CB1R in zebrafish. Together, these results raise the likely possibility that embryonic exposure to low doses of CB1R-interfering compounds could impact on the development of the neuroendocrine systems controlling sexual maturation, reproduction and food intake.
Topics: Agouti-Related Protein; Animals; Axons; Benzoxazines; Embryo, Nonmammalian; Embryonic Development; Gonadotropin-Releasing Hormone; Morpholines; Morpholinos; Naphthalenes; Neurons; Pyrrolidonecarboxylic Acid; Receptor, Cannabinoid, CB1; Zebrafish; Zebrafish Proteins
PubMed: 31881740
DOI: 10.3390/ijms21010168 -
BioRxiv : the Preprint Server For... Mar 2024Specific and highly diverse connectivity between functionally specialized regions of the nervous system is controlled at multiple scales, from anatomically organized...
Specific and highly diverse connectivity between functionally specialized regions of the nervous system is controlled at multiple scales, from anatomically organized connectivity following macroscopic axon tracts to individual axon target-finding and synapse formation. Identifying mechanisms that enable entire subpopulations of related neurons to project their axons with regional specificity within stereotyped tracts to form appropriate long-range connectivity is key to understanding brain development, organization, and function. Here, we investigate how axons of the cerebral cortex form precise connections between the two cortical hemispheres via the corpus callosum. We identify topographic principles of the developing trans-hemispheric callosal tract that emerge through intrinsic guidance executed by growing axons in the corpus callosum within the first postnatal week in mice. Using micro-transplantation of regionally distinct neurons, subtype-specific growth cone purification, subcellular proteomics, and in utero gene manipulation, we investigate guidance mechanisms of transhemispheric axons. We find that adhesion molecule levels instruct tract topography and target field guidance. We propose a model in which transcallosal axons in the developing brain perform a "handshake" that is guided through co-fasciculation with symmetric contralateral axons, resulting in the stereotyped homotopic connectivity between the brain's hemispheres.
PubMed: 38585721
DOI: 10.1101/2024.03.28.587108 -
Neural Development Oct 2014Peripheral nerve injuries can severely affect the way that animals perceive signals from the surrounding environment. While damage to peripheral axons generally has a...
BACKGROUND
Peripheral nerve injuries can severely affect the way that animals perceive signals from the surrounding environment. While damage to peripheral axons generally has a better outcome than injuries to central nervous system axons, it is currently unknown how neurons re-establish their target innervations to recover function after injury, and how accessory cells contribute to this task. Here we use a simple technique to create reproducible and localized injury in the posterior lateral line (pLL) nerve of zebrafish and follow the fate of both neurons and Schwann cells.
RESULTS
Using pLL single axon labeling by transient transgene expression, as well as transplantation of glial precursor cells in zebrafish larvae, we individualize different components in this system and characterize their cellular behaviors during the regenerative process. Neurectomy is followed by loss of Schwann cell differentiation markers that is reverted after nerve regrowth. We show that reinnervation of lateral line hair cells in neuromasts during pLL nerve regeneration is a highly dynamic process with promiscuous yet non-random target recognition. Furthermore, Schwann cells are required for directional extension and fasciculation of the regenerating nerve. We provide evidence that these cells and regrowing axons are mutually dependant during early stages of nerve regeneration in the pLL. The role of ErbB signaling in this context is also explored.
CONCLUSION
The accessibility of the pLL nerve and the availability of transgenic lines that label this structure and their synaptic targets provides an outstanding in vivo model to study the different events associated with axonal extension, target reinnervation, and the complex cellular interactions between glial cells and injured axons during nerve regeneration.
Topics: Analysis of Variance; Animals; Animals, Genetically Modified; Axons; Bromodeoxyuridine; Cell Transplantation; DNA-Binding Proteins; Disease Models, Animal; Embryo, Nonmammalian; Green Fluorescent Proteins; Larva; Nerve Regeneration; Nerve Tissue Proteins; Oncogene Proteins v-erbB; Peripheral Nerve Injuries; Schwann Cells; Signal Transduction; Zebrafish; Zebrafish Proteins
PubMed: 25326036
DOI: 10.1186/1749-8104-9-22 -
Development (Cambridge, England) Jul 2017Visual information is relayed from the eye to the brain via retinal ganglion cell (RGC) axons. Mice lacking NRP1 or NRP1-binding VEGF-A isoforms have defective RGC axon...
Visual information is relayed from the eye to the brain via retinal ganglion cell (RGC) axons. Mice lacking NRP1 or NRP1-binding VEGF-A isoforms have defective RGC axon organisation alongside brain vascular defects. It is not known whether axonal defects are caused exclusively by defective VEGF-A signalling in RGCs or are exacerbated by abnormal vascular morphology. Targeted NRP1 ablation in RGCs with a knock-in allele reduced axonal midline crossing at the optic chiasm and optic tract fasciculation. In contrast, -mediated endothelial NRP1 ablation induced axon exclusion zones in the optic tracts without impairing axon crossing. Similar defects were observed in and mice, which have vascular defects as a result of their expression of single VEGF-A isoforms. Ectopic midline vascularisation in endothelial and mutants caused additional axonal exclusion zones within the chiasm. As and assays demonstrated that vessels do not repel axons, abnormally large or ectopically positioned vessels are likely to present physical obstacles to axon growth. We conclude that proper axonal wiring during brain development depends on the precise molecular control of neurovascular co-patterning.
Topics: Animals; Axons; Blood Vessels; Body Patterning; Central Nervous System; Diencephalon; Endothelial Cells; Gene Knockdown Techniques; Homeodomain Proteins; Mice, Inbred C57BL; Mutation; Neovascularization, Physiologic; Neuropilin-1; Optic Chiasm; Retinal Ganglion Cells; Transcription Factor Brn-3B; Vascular Endothelial Growth Factor A; Visual Pathways
PubMed: 28676569
DOI: 10.1242/dev.151621 -
Muscle & Nerve Jul 2017We compared the yield of limb and thoracic paraspinal muscle examination for revealing lower motor neuron (LMN) dysfunction on electromyography (EMG) in amyotrophic...
INTRODUCTION
We compared the yield of limb and thoracic paraspinal muscle examination for revealing lower motor neuron (LMN) dysfunction on electromyography (EMG) in amyotrophic lateral sclerosis (ALS).
METHODS
A retrospective review of 354 patients with clinically definite or probable ALS was performed. Seventeen limb muscles and thoracic paraspinal muscles were evaluated for the presence of both active and chronic denervation.
RESULTS
Distal limb muscles showed the highest electrodiagnostic sensitivities of LMN dysfunction in ALS regardless of onset region and diagnostic certainty at the time of diagnosis. Electrodiagnostic yield is higher in muscles from the onset limb. Noncontiguous spread of lower motor neuron degeneration is present in ALS. Optimally selected 6 upper and 5 lower extremity muscles yielded >98% of potential positive cervical or lumbosacral segments.
CONCLUSIONS
An algorithmic approach to needle EMG in ALS based on pretest probability of individual muscles optimizes electrodiagnostic yield, thus possibly minimizing test duration and patient discomfort. Muscle Nerve 56: 36-44, 2017.
Topics: Adult; Aged; Aged, 80 and over; Algorithms; Amyotrophic Lateral Sclerosis; Cohort Studies; Electromyography; Extremities; Female; Humans; Lumbosacral Region; Male; Middle Aged; Muscle, Skeletal; Young Adult
PubMed: 27759887
DOI: 10.1002/mus.25444 -
BioRxiv : the Preprint Server For... Feb 2024The chromodomain helicase binding protein 4 (CHD4) is an ATP-dependent chromatin remodeler. pathogenic variants of cause Sifrim-Hitz-Weiss syndrome (SIHIWES). Patients...
The chromodomain helicase binding protein 4 (CHD4) is an ATP-dependent chromatin remodeler. pathogenic variants of cause Sifrim-Hitz-Weiss syndrome (SIHIWES). Patients with SIHIWES show delayed development, intellectual disability, facial dysmorphism, and hearing loss. Many cochlear cell types, including spiral ganglion neurons (SGNs), express CHD4. SGNs are the primary afferent neurons that convey sound information from the cochlea, but the function of CHD4 in SGNs is unknown. We employed the Neurog1(Ngn1) CreERT conditional knockout animals to delete in SGNs. SGNs are classified as type I and type II neurons. SGNs lacking CHD4 showed abnormal fasciculation of type I neurons along with improper pathfinding of type II fibers. CHD4 binding to chromatin from immortalized multipotent otic progenitor-derived neurons was used to identify candidate target genes in SGNs. Gene ontology analysis of CHD4 target genes revealed cellular processes involved in axon guidance, axonal fasciculation, and ephrin receptor signaling pathway. We validated increased transcripts in SGNs from conditional knockout cochleae. The results suggest that CHD4 attenuates the transcription of axon guidance genes to form the stereotypic pattern of SGN peripheral projections. The results implicate epigenetic changes in circuit wiring by modulating axon guidance molecule expression and provide insights into neurodevelopmental diseases.
PubMed: 38352369
DOI: 10.1101/2024.01.31.578202 -
Functional divergence of Plexin B structural motifs in distinct steps of olfactory circuit assembly.ELife Jun 2019Plexins exhibit multitudinous, evolutionarily conserved functions in neural development. How Plexins employ their diverse structural motifs in vivo to perform distinct...
Plexins exhibit multitudinous, evolutionarily conserved functions in neural development. How Plexins employ their diverse structural motifs in vivo to perform distinct roles is unclear. We previously reported that Plexin B (PlexB) controls multiple steps during the assembly of the olfactory circuit (Li et al., 2018b). Here, we systematically mutagenized structural motifs of PlexB and examined the function of these variants in these multiple steps: axon fasciculation, trajectory choice, and synaptic partner selection. We found that the extracellular Sema domain is essential for all three steps, the catalytic site of the intracellular RapGAP is engaged in none, and the intracellular GTPase-binding motifs are essential for trajectory choice and synaptic partner selection, but are dispensable for fasciculation. Moreover, extracellular PlexB cleavage serves as a regulatory mechanism of PlexB signaling. Thus, the divergent roles of PlexB motifs in distinct steps of neural development contribute to its functional versatility in neural circuit assembly.
Topics: Animals; Animals, Genetically Modified; Axons; Drosophila Proteins; Drosophila melanogaster; Nerve Tissue Proteins; Neurogenesis; Olfactory Bulb; Receptors, Cell Surface; Semaphorins; Signal Transduction; Smell
PubMed: 31225795
DOI: 10.7554/eLife.48594 -
Frontiers in Bioengineering and... 2024Motor nerve organoids could be generated by culturing a spheroid of motor neurons differentiated from human induced pluripotent stem (iPS) cells within a...
Motor nerve organoids could be generated by culturing a spheroid of motor neurons differentiated from human induced pluripotent stem (iPS) cells within a polydimethylsiloxane (PDMS) chip which guides direction and fasciculation of axons extended from the spheroid. To isolate axon bundles from motor nerve organoids, we developed a rapid laser dissection method based on localized photothermal combustion. By illuminating a blue laser on a black mark on the culture device using a dry-erase marker, we induced highly localized heating near the axon bundles. Moving the laser enabled spatial control over the local heating and severing of axon bundles. This laser dissection requires a black mark, as other colors did not produce the same localized heating effect. A CO laser destroyed the tissue and the device and could not be used. With this simple, economical laser dissection technique, we could rapidly collect abundant pure axon samples from motor nerve organoids for biochemical analysis. Extracted axonal proteins and RNA were indistinguishable from manual dissection. This method facilitates efficient axon isolation for further analyses.
PubMed: 38347914
DOI: 10.3389/fbioe.2024.1259138 -
Science Signaling Aug 2014Axon guidance (pathfinding) wires the brain during development and is regulated by various attractive and repulsive cues. Semaphorin 3A (Sema3A) is a repulsive cue,...
Axon guidance (pathfinding) wires the brain during development and is regulated by various attractive and repulsive cues. Semaphorin 3A (Sema3A) is a repulsive cue, inducing the collapse of axon growth cones. In the mammalian forebrain, the corpus callosum is the major commissure that transmits information flow between the two hemispheres, and contralateral axons assemble into well-defined tracts. We found that the patterning of callosal axon projections in rodent layer II and III (L2/3) cortical neurons in response to Sema3A was mediated by the activation of Rab5, a small guanosine triphosphatase (GTPase) that mediates endocytosis, through the membrane fusion protein Rabaptin-5 and the Rab5 guanine nucleotide exchange factor (GEF) Rabex-5. Rabaptin-5 bound directly to Plexin-A1 in the Sema3A receptor complex [an obligate heterodimer formed by Plexin-A1 and neuropilin 1 (NP1)]; Sema3A enhanced this interaction in cultured neurons. Rabaptin-5 bridged the interaction between Rab5 and Plexin-A1. Sema3A stimulated endocytosis from the cell surface of callosal axon growth cones. In utero electroporation to reduce Rab5 or Rabaptin-5 impaired axon fasciculation or caused mistargeting of L2/3 callosal projections in rats. Overexpression of Rabaptin-5 or Rab5 rescued the defective callosal axon fasciculation or mistargeting of callosal axons caused by the loss of Sema3A-Plexin-A1 signaling in rats expressing dominant-negative Plexin-A1 or in NP1-deficient mice. Thus, our findings suggest that Rab5, its effector Rabaptin-5, and its regulator Rabex-5 mediate Sema3A-induced axon guidance during brain development.
Topics: Animals; Axons; Corpus Callosum; Electroporation; Enzyme Activation; Growth Cones; Guanine Nucleotide Exchange Factors; HEK293 Cells; Humans; Immunoprecipitation; Mice; Mice, Mutant Strains; Microfluidics; Microscopy, Confocal; Nerve Tissue Proteins; Neuropilin-1; RNA, Small Interfering; Rats; Receptors, Cell Surface; Recombinant Proteins; Semaphorin-3A; Transfection; Vesicular Transport Proteins; rab5 GTP-Binding Proteins
PubMed: 25161316
DOI: 10.1126/scisignal.2005334