-
Frontiers in Neuroanatomy 2021Axon guidance proteins play key roles in the formation of neural circuits during development. We previously identified an axon guidance cue, named draxin, that has no... (Review)
Review
Axon guidance proteins play key roles in the formation of neural circuits during development. We previously identified an axon guidance cue, named draxin, that has no homology with other axon guidance proteins. Draxin is essential for the development of various neural circuits including the spinal cord commissure, corpus callosum, and thalamocortical projections. Draxin has been shown to not only control axon guidance through netrin-1 receptors, deleted in colorectal cancer (Dcc), and neogenin (Neo1) but also modulate netrin-1-mediated axon guidance and fasciculation. In this review, we summarize the multifaceted functions of draxin and netrin-1 signaling in neural circuit formation in the central nervous system. Furthermore, because recent studies suggest that the distributions and functions of axon guidance cues are highly regulated by glycoproteins such as Dystroglycan and Heparan sulfate proteoglycans, we discuss a possible function of glycoproteins in draxin/netrin-1-mediated axon guidance.
PubMed: 34899198
DOI: 10.3389/fnana.2021.766911 -
Journal of Tissue Engineering and... Feb 2022Three dimensional (3D) in vitro neuronal cultures can better reproduce physiologically relevant phenotypes compared to 2D-cultures, because in vivo neurons reside in a...
Three dimensional (3D) in vitro neuronal cultures can better reproduce physiologically relevant phenotypes compared to 2D-cultures, because in vivo neurons reside in a 3D microenvironment. Interest in neuronal 3D cultures is emerging, with special attention to the mechanical forces that regulate axon elongation and sprouting in three dimensions. Type I collagen (Col-I) is a native substrate since it is present in the extracellular matrix and hence emulates an in vivo environment to study axon growth. The impact of its mechanical properties needs to be further investigated. Here, we generated Col-I 3D matrices of different mechanical stiffness and evaluated axon growth in three dimensions. Superior cervical ganglion (SCG) explants from neonatal rats were cultured in soft and stiff Col-I 3D matrices and neurite outgrowth was assessed by measuring: maximum neuritic extent; neuritic halo area and fasciculation. Axonal cytoskeletal proteins were examined. Axon elongation in stiff Col-I 3D matrices was reduced (31%) following 24 h in culture compared to soft matrices. In stiff matrices, neurites fasciculated and formed less dense halos. Consistently, almost no F-actin rich growth cones were recognized, and F-actin staining was strongly reduced in the axonal compartment. This study shows that stiffness negatively affects 3D neurite outgrowth and adds insights on the cytoskeletal responses upon mechanic interactions of axons with a 3D environment. Our data will serve to facilitate the development of model systems that are mechanically well-behaved but still mimic key physiologic properties observed in vivo.
Topics: Actins; Animals; Axons; Cells, Cultured; Collagen Type I; Extracellular Matrix; Growth Cones; Neurites; Rats
PubMed: 34816618
DOI: 10.1002/term.3269 -
Journal of Developmental Biology Oct 2021The extracellular matrix (ECM) guides and constrains the shape of the nervous system. In , DIG-1 is a giant ECM component that is required for fasciculation of sensory...
The extracellular matrix (ECM) guides and constrains the shape of the nervous system. In , DIG-1 is a giant ECM component that is required for fasciculation of sensory dendrites during development and for maintenance of axon positions throughout life. We identified four novel alleles of in three independent screens for mutants affecting disparate aspects of neuronal and glial morphogenesis. First, we find that disruption of DIG-1 causes fragmentation of the amphid sheath glial cell in larvae and young adults. Second, it causes severing of the BAG sensory dendrite from its terminus at the nose tip, apparently due to breakage of the dendrite as animals reach adulthood. Third, it causes embryonic defects in dendrite fasciculation in inner labial (IL2) sensory neurons, as previously reported, as well as rare defects in IL2 dendrite extension that are enhanced by loss of the apical ECM component DYF-7, suggesting that apical and basolateral ECM contribute separately to dendrite extension. Our results highlight novel roles for DIG-1 in maintaining the cellular integrity of neurons and glia, possibly by creating a barrier between structures in the nervous system.
PubMed: 34698211
DOI: 10.3390/jdb9040042 -
Neural Regeneration Research May 2022The formation of nerve bundles, which is partially regulated by neural cell adhesion molecule 1 (NCAM1), is important for neural network organization during peripheral...
The formation of nerve bundles, which is partially regulated by neural cell adhesion molecule 1 (NCAM1), is important for neural network organization during peripheral nerve regeneration. However, little is known about how the extracellular matrix (ECM) microenvironment affects this process. Here, we seeded dorsal root ganglion tissue blocks on different ECM substrates of peripheral nerve ECM-derived matrix-gel, Matrigel, laminin 521, collagen I, and collagen IV, and observed well-aligned axon bundles growing in the peripheral nerve ECM-derived environment. We confirmed that NCAM1 is necessary but not sufficient to trigger this phenomenon. A protein interaction assay identified collagen VI as an extracellular partner of NCAM1 in the regulation of axonal fasciculation. Collagen VI interacted with NCAM1 by directly binding to the FNIII domain, thereby increasing the stability of NCAM1 at the axolemma. Our in vivo experiments on a rat sciatic nerve defect model also demonstrated orderly nerve bundle regeneration with improved projection accuracy and functional recovery after treatment with 10 mg/mL Matrigel and 20 μg/mL collagen VI. These findings suggest that the collagen VI-NCAM1 pathway plays a regulatory role in nerve bundle formation. This study was approved by the Animal Ethics Committee of Guangzhou Medical University (approval No. GY2019048) on April 30, 2019.
PubMed: 34558529
DOI: 10.4103/1673-5374.324861 -
Molecules and Cells Aug 2021Decoding the molecular mechanisms underlying axon guidance is key to precise understanding of how complex neural circuits form during neural development. Although... (Review)
Review
Decoding the molecular mechanisms underlying axon guidance is key to precise understanding of how complex neural circuits form during neural development. Although substantial progress has been made over the last three decades in identifying numerous axon guidance molecules and their functional roles, little is known about how these guidance molecules collaborate to steer growth cones to their correct targets. Recent studies in point to the importance of the combinatorial action of guidance molecules, and further show that selective fasciculation and defasciculation at specific choice points serve as a fundamental strategy for motor axon guidance. Here, I discuss how attractive and repulsive guidance cues cooperate to ensure the recognition of specific choice points that are inextricably linked to selective fasciculation and defasciculation, and correct pathfinding decision-making.
Topics: Animals; Axon Fasciculation; Axon Guidance; Drosophila melanogaster; Motor Neurons; Muscles; Neuromuscular Junction
PubMed: 34385406
DOI: 10.14348/molcells.2021.0129 -
Frontiers in Neural Circuits 2021Precise positioning of neurons resulting from cell division and migration during development is critical for normal brain function. Disruption of neuronal migration can...
Precise positioning of neurons resulting from cell division and migration during development is critical for normal brain function. Disruption of neuronal migration can cause a myriad of neurological disorders. To investigate the functional consequences of defective neuronal positioning on circuit function, we studied a zebrafish () loss-of-function mutant () where the facial branchiomotor (FBM) neurons fail to migrate out of their birthplace. A jaw movement assay, which measures the opening of the zebrafish jaw (gape), showed that the frequency of gape events, but not their amplitude, was decreased in mutants. Consistent with this, a larval feeding assay revealed decreased food intake in mutants, indicating that the FBM circuit in mutants generates defective functional outputs. We tested various mechanisms that could generate defective functional outputs in mutants. While is ubiquitously expressed in neural and non-neural tissues, jaw cartilage and muscle developed normally in mutants, and muscle function also appeared to be unaffected. Although FBM neurons were mispositioned in mutants, axon pathfinding to jaw muscles was unaffected. Moreover, neuromuscular junctions established by FBM neurons on jaw muscles were similar between wildtype siblings and mutants. Interestingly, motor axons innervating the interhyoideus jaw muscle were frequently defasciculated in mutants. Furthermore, GCaMP imaging revealed that mutant FBM neurons were less active than their wildtype counterparts. These data show that aberrant positioning of FBM neurons in mutants is correlated with subtle defects in fasciculation and neuronal activity, potentially generating defective functional outputs.
Topics: Animals; Axons; Cell Movement; Motor Neurons; Neurogenesis; Zebrafish; Zebrafish Proteins
PubMed: 34248505
DOI: 10.3389/fncir.2021.690475 -
ENeuro 2021Elaboration of neuronal processes is an early step in neuronal development. Guidance cues must work closely with intracellular trafficking pathways to direct expanding...
Elaboration of neuronal processes is an early step in neuronal development. Guidance cues must work closely with intracellular trafficking pathways to direct expanding axons and dendrites to their target neurons during the formation of neuronal networks. However, how such coordination is achieved remains incompletely understood. Here, we characterize an interaction between fasciculation and elongation protein zeta 1 (FEZ1), an adapter involved in synaptic protein transport, and collapsin response mediator protein (CRMP)1, a protein that functions in growth cone guidance, at neuronal growth cones. We show that similar to CRMP1 loss-of-function mutants, FEZ1 deficiency in rat hippocampal neurons causes growth cone collapse and impairs axonal development. Strikingly, FEZ1-deficient neurons also exhibited a reduction in dendritic complexity stronger than that observed in CRMP1-deficient neurons, suggesting that the former could partake in additional developmental signaling pathways. Supporting this, FEZ1 colocalizes with VAMP2 in developing hippocampal neurons and forms a separate complex with deleted in colorectal cancer (DCC) and Syntaxin-1 (Stx1), components of the Netrin-1 signaling pathway that are also involved in regulating axon and dendrite development. Significantly, developing axons and dendrites of FEZ1-deficient neurons fail to respond to Netrin-1 or Netrin-1 and Sema3A treatment, respectively. Taken together, these findings highlight the importance of FEZ1 as a common effector to integrate guidance signaling pathways with intracellular trafficking to mediate axo-dendrite development during neuronal network formation.
Topics: Adaptor Proteins, Signal Transducing; Animals; Axons; DCC Receptor; Growth Cones; Nerve Tissue Proteins; Neurons; Rats; Receptors, Cell Surface
PubMed: 33771901
DOI: 10.1523/ENEURO.0193-20.2021 -
Journal of Molecular and Cellular... May 2021The intracardiac nervous system (ICNS) is composed of neurons, in association with Schwann cells (SC) and endoneurial cardiac fibroblasts (ECF). Besides heart rhythm...
BACKGROUND
The intracardiac nervous system (ICNS) is composed of neurons, in association with Schwann cells (SC) and endoneurial cardiac fibroblasts (ECF). Besides heart rhythm control, recent studies have implicated cardiac nerves in postnatal cardiac regeneration and cardiomyocyte size regulation, but cardiac SC and ECF remain understudied. During the postnatal period, the ICNS undergoes intense remodeling with nerve fasciculation and elongation throughout the myocardium, partially guided by the extracellular matrix (ECM). Here we report the origins, heterogeneity, and functions of SC and ECF that develop in proximity to neurons during postnatal ICNS maturation.
METHODS AND RESULTS
Periostin lineage (Postn+) cells include cardiac Remak SC and ECF during the postnatal period in mice. The developmental origins of cardiac SC and ECF were examined using Rosa26 reporter mice bred with Wnt1Cre, expressed in Neural crest (NC)-derived lineages, or tamoxifen-inducible Tcf21MerCreMer, expressed predominantly in epicardial-derived fibroblast lineages. ICNS components are NC-derived with the exceptions of the myelinating Plp1+ SC and the Tcf21+ lineage-derived intramural ventricular ECF. In addition, Postn+ lineage GFAP- Remak SC and ECF are present around the fasciculating cardiac nerves. Whole mount studies of the NC-derived cells confirmed postnatal maturation of the complex ICNS network from P0 to P30. Sympathetic, parasympathetic, and sensory neurons fasciculate from P0 to P7 indicated by co-staining with PSA-NCAM. Ablation of Postn+ cells from P0 to P6 or loss of Periostin leads to reduced fasciculation of cardiac sympathetic nerves. In addition, collagen remodeling surrounding maturing nerves of the postnatal heart is reduced in Postn-null mice.
CONCLUSIONS
Postn+ cells include cardiac SC and ECF during postnatal nerve maturation, and these cells have different embryonic origins. At P7, the Postn+ cells associated with cardiac nerves are mainly Remak SC and ECF. Ablation of the Postn+ cells from P0 to P6 and also loss of Postn in Postn-null mice leads to reduced fasciculation of cardiac nerves at P7.
Topics: Animals; Axon Fasciculation; Cell Adhesion Molecules; Fibroblasts; Gene Expression; Mice; Schwann Cells; Sympathetic Nervous System
PubMed: 33582160
DOI: 10.1016/j.yjmcc.2021.02.001 -
Investigative Ophthalmology & Visual... Jan 2021The three-dimensional configurations of rod and cone bipolar cell (BC) dendrites and horizontal cell (HC) processes outside rod and cone synaptic terminals have not been...
PURPOSE
The three-dimensional configurations of rod and cone bipolar cell (BC) dendrites and horizontal cell (HC) processes outside rod and cone synaptic terminals have not been fully elucidated. We reveal how these neurites are mutually arranged to coordinate formation and maintenance of the postsynaptic complex of ribbon synapses in mouse and monkey retinas.
METHODS
Serial section transmission electron microscopy was utilized to reconstruct BC and HC neurites in macaque monkey and mouse, including metabotropic glutamate receptor 6 (mGluR6)-knockout mice.
RESULTS
Starting from sporadically distributed branching points, rod BC and HC neurites (B and H, respectively) took specific paths to rod spherules by gradually adjusting their mutual positions, which resulted in a closed alternating pattern of H‒B‒H‒B neurites at the rod spherule aperture. This order corresponded to the array of elements constituting the postsynaptic complex of ribbon synapses. We identified novel helical coils of HC processes surrounding the rod BC dendrite in both mouse and macaque retinas, and these structures occurred more frequently in mGluR6-knockout than wild-type mouse retinas. Horizontal cell processes also formed hook-like protrusions that encircled cone BC and HC neurites below the cone pedicles in the macaque retina.
CONCLUSIONS
Bipolar and horizontal cell neurites take specific paths to adjust their mutual positions at the rod spherule aperture. Some HC processes are helically coiled around rod BC dendrites or form hook-like protrusions around cone BC dendrites and HC processes. Loss of mGluR6 signaling may be one factor promoting unbalanced neurite growth and compensatory neurite coiling.
Topics: Animals; Axon Fasciculation; Female; Macaca fuscata; Male; Mice; Mice, Inbred C57BL; Mice, Knockout; Microscopy, Electron, Transmission; Neurites; Presynaptic Terminals; Receptors, Metabotropic Glutamate; Retinal Bipolar Cells; Retinal Horizontal Cells; Retinal Rod Photoreceptor Cells; Synapses; Visual Pathways
PubMed: 33507230
DOI: 10.1167/iovs.62.1.31 -
Cells Dec 2020During brain development, neurons need to form the correct connections with one another in order to give rise to a functional neuronal circuitry. Mistakes during this... (Review)
Review
During brain development, neurons need to form the correct connections with one another in order to give rise to a functional neuronal circuitry. Mistakes during this process, leading to the formation of improper neuronal connectivity, can result in a number of brain abnormalities and impairments collectively referred to as neurodevelopmental disorders. Cell adhesion molecules (CAMs), present on the cell surface, take part in the neurodevelopmental process regulating migration and recognition of specific cells to form functional neuronal assemblies. Among CAMs, the members of the protocadherin (PCDH) group stand out because they are involved in cell adhesion, neurite initiation and outgrowth, axon pathfinding and fasciculation, and synapse formation and stabilization. Given the critical role of these macromolecules in the major neurodevelopmental processes, it is not surprising that clinical and basic research in the past two decades has identified several genes as responsible for a large fraction of neurodevelopmental disorders. In the present article, we review these findings with a focus on the non-clustered PCDH sub-group, discussing the proteins implicated in the main neurodevelopmental disorders.
Topics: Amino Acid Motifs; Animals; Axons; Cadherins; Cell Adhesion; Cell Adhesion Molecules; Cell Movement; Cell Proliferation; Dendrites; Humans; Multigene Family; Mutation; Neurites; Neurodevelopmental Disorders; Neurogenesis; Neurons; Protein Isoforms; Protocadherins; Synapses; Tissue Distribution
PubMed: 33352832
DOI: 10.3390/cells9122711