Search

During neurogenesis, excessive numbers of neurons are produced in most regions of the central and peripheral nervous systems. Nonessential neurons are eliminated by apoptosis, or programmed cell death. This has been most thoroughly characterized in the peripheral nervous system (PNS) where targets of innervation play a key role in this process. As maturing neurons project axons towards their targets of innervation, they become dependent upon these targets for survival. Survival factors, also called neurotrophic factors, are produced by targets, inhibit apoptosis cascades, and promote further growth and differentiation. Because neurotrophic factors are limited, as is target size, neurons that do not correctly and efficiently innervate targets undergo apoptosis ( Levi-Montalcini, 1987; Davies, 1996). Thus, excessive neurogenesis acts to ensure that sufficient numbers of neurons are produced during development. In the superior cervical ganglion (SCG), this process of neurogenesis and subsequent apoptosis is reported to be complete by postnatal day 3-4 (P3-P4) in mice. Surprisingly, we observed significant numbers of apoptotic neurons out to P14, and neurogenesis was still present at P14 as well. In both the SCG and geniculate ganglion (GG), postnatal neurogenesis was dependent on apoptosis because little or no postnatal neurogenesis was observed in Bax-/- mice, in which apoptosis is eliminated. These results indicate that both neurogenesis and apoptosis continue to occur well after birth in peripheral ganglia, and that neurogenesis depends on apoptosis, suggesting that neurogenesis continues postnatally to replace neurons that are eliminated during synaptic refinement., Competing Interests: Competing interests The authors declare no competing or financial interests., (© 2024. Published by The Company of Biologists Ltd.)

Glial cells are essential for the proper development and functioning of the peripheral nervous system (PNS). The ability to study the biology of glial cells is therefore critical for our ability to understand PNS biology and address PNS maladies. The genetic and proteomic pathways underlying vertebrate peripheral glial biology are understandably complex, with many layers of redundancy making it sometimes difficult to study certain facets of PNS biology. Fortunately, many aspects of vertebrate peripheral glial biology are conserved with those of the fruit fly, Drosophila melanogaster With simple and powerful genetic tools and fast generation times, Drosophila presents an accessible and versatile model for studying the biology of peripheral glia. We introduce here three techniques for studying the cell biology of peripheral glia of Drosophila third-instar larvae. With fine dissection tools and common laboratory reagents, third-instar larvae can be dissected, with extraneous tissues removed, revealing the central nervous system (CNS) and PNS to be processed using a standard immunolabeling protocol. To improve the resolution of peripheral nerves in the z -plane, we describe a cryosectioning method to achieve 10- to 20-µm thick coronal sections of whole larvae, which can then be immunolabeled using a modified version of standard immunolabeling techniques. Finally, we describe a proximity ligation assay (PLA) for detecting close proximity between two proteins-thus inferring protein interaction-in vivo in third-instar larvae. These methods, further described in our associated protocols, can be used to improve our understanding of Drosophila peripheral glia biology, and thus our understanding of PNS biology., (© 2024 Cold Spring Harbor Laboratory Press.)

Despite extensive research, there is still no treatment that would lead to remission in all patients with rheumatoid arthritis as our understanding of the affected site, the synovium, is still incomplete. Recently, single-cell technologies helped to decipher the cellular heterogeneity of the synovium; however, certain synovial cell populations, such as endothelial cells or peripheral neurons, remain to be profiled on a single-cell level. Furthermore, associations between certain cellular states and inflammation were found; whether these cells cause the inflammation remains to be answered. Similarly, cellular zonation and interactions between individual effectors in the synovium are yet to be fully determined. A deeper understanding of cell signalling and interactions in the synovium is crucial for a better design of therapeutics with the goal of complete remission in all patients., (© The Author(s) 2021. Published by Oxford University Press on behalf of the British Society for Rheumatology.)

The peripheral nervous system consists of sensory circuits that respond to external and internal stimuli and effector circuits that adapt physiologic functions to environmental challenges. Identifying neurotransmitters and neuropeptides and the corresponding receptors on immune cells implies an essential role for the nervous system in regulating immune reactions. Vice versa, neurons express functional cytokine receptors to respond to inflammatory signals directly. Recent advances in single-cell and single-nuclei sequencing have provided an unprecedented depth in neuronal analysis and allowed to refine the classification of distinct neuronal subsets of the peripheral nervous system. Delineating the sensory and immunoregulatory capacity of different neuronal subsets could inform a better understanding of the response happening in tissues that coordinate physiologic functions, tissue homeostasis and immunity. Here, we summarize current subsets of peripheral neurons and discuss neuronal regulation of immune responses, focusing on neuro-immune interactions in the gastrointestinal tract. The nervous system as a central coordinator of immune reactions and tissue homeostasis may predispose for novel promising therapeutic approaches for a large variety of diseases including but not limited to chronic inflammation., Competing Interests: The authors declare that the research was conducted in the absence of any commercial or financial relationships that could be construed as a potential conflict of interest., (Copyright © 2021 Jakob, Kofoed-Branzk, Deshpande, Murugan and Klose.)

Stem cell technologies including self-assembling 3D tissue models provide access to early human neurodevelopment and fundamental insights into neuropathologies. Gastruloid models have not been used to investigate co-developing central and peripheral neuronal systems with trunk mesendoderm which we achieve here in elongating multi-lineage organized (EMLO) gastruloids. We evaluate EMLOs over a forty-day period, applying immunofluorescence of multi-lineage and functional biomarkers, including day 16 single-cell RNA-Seq, and evaluation of ectodermal and non-ectodermal neural crest cells (NCCs). We identify NCCs that differentiate to form peripheral neurons integrated with an upstream spinal cord region after day 8. This follows initial EMLO polarization events that coordinate with endoderm differentiation and primitive gut tube formation during multicellular spatial reorganization. This combined human central-peripheral nervous system model of early organogenesis highlights developmental events of mesendoderm and neuromuscular trunk regions and enables systemic studies of tissue interactions and innervation of neuromuscular, enteric and cardiac relevance.

For a long time, neurogenic placodes and migratory neural crest cells were considered the immediate sources building neurons of peripheral nervous system. Recently, a number of discoveries revealed the existence of another progenitor type-a nerve-associated multipotent Schwann cell precursors (SCPs) building enteric and parasympathetic neurons as well as neuroendocrine chromaffin cells. SCPs are neural crest-derived and are similar to the crest cells by their markers and differentiation potential. Such similarities, but also considerable differences, raise many questions pertaining to the medical side, fundamental developmental biology and evolution. Here, we discuss the genesis of Schwann cell precursors, their role in building peripheral neural structures and ponder on their role in the origin in congenial diseases associated with peripheral nervous systems.

The functionality of the nervous system requires transmission of information along axons with high speed and precision. Conductance velocity depends on axonal diameter whereas signaling precision requires a block of electrical crosstalk between axons, known as ephaptic coupling. Here, we use the peripheral nervous system of Drosophila larvae to determine how glia regulates axonal properties. We show that wrapping glial differentiation depends on gap junctions and FGF-signaling. Abnormal glial differentiation affects axonal diameter and conductance velocity and causes mild behavioral phenotypes that can be rescued by a sphingosine-rich diet. Ablation of wrapping glia does not further impair axonal diameter and conductance velocity but causes a prominent locomotion phenotype that cannot be rescued by sphingosine. Moreover, optogenetically evoked locomotor patterns do not depend on conductance speed but require the presence of wrapping glial processes. In conclusion, our data indicate that wrapping glia modulates both speed and precision of neuronal signaling.

Myelin protein zero (P0), a type I transmembrane protein, is the most abundant protein in peripheral nervous system (PNS) myelin-the lipid-rich, periodic structure of membrane pairs that concentrically encloses long axonal segments. Schwann cells, the myelinating glia of the PNS, express P0 throughout their development until the formation of mature myelin. In the intramyelinic compartment, the immunoglobulin-like domain of P0 bridges apposing membranes via homophilic adhesion, forming, as revealed by electron microscopy, the electron-dense, double "intraperiod line" that is split by a narrow, electron-lucent space corresponding to the extracellular space between membrane pairs. The C-terminal tail of P0 adheres apposing membranes together in the narrow cytoplasmic compartment of compact myelin, much like myelin basic protein (MBP). In mouse models, the absence of P0, unlike that of MBP or P2, severely disturbs myelination. Therefore, P0 is the executive molecule of PNS myelin maturation. How and when P0 is trafficked and modified to enable myelin compaction, and how mutations that give rise to incurable peripheral neuropathies alter the function of P0, are currently open questions. The potential mechanisms of P0 function in myelination are discussed, providing a foundation for the understanding of mature myelin development and how it derails in peripheral neuropathies.

Whereas microglia are recognized as fundamental players in central nervous system (CNS) development and function, much less is known about macrophages of the peripheral nervous system (PNS). Here, by comparing gene expression across neural and conventional tissue-resident macrophages, we identified transcripts that were shared among neural resident macrophages as well as selectively enriched in PNS macrophages. Remarkably, PNS macrophages constitutively expressed genes previously identified to be upregulated by activated microglia during aging, neurodegeneration, or loss of Sall1. Several microglial activation-associated and PNS macrophage-enriched genes were also expressed in spinal cord microglia at steady state. We further show that PNS macrophages rely on IL-34 for maintenance and arise from both embryonic and hematopoietic precursors, while their expression of activation-associated genes did not differ by ontogeny. Collectively, these data uncover shared and unique features between neural resident macrophages and emphasize the role of nerve environment for shaping PNS macrophage identity.

Mammals differ in their regeneration potential after traumatic injury, which might be caused by species-specific regeneration programs. Here, we compared murine and human Schwann cell (SC) response to injury and developed an ex vivo injury model employing surgery-derived human sural nerves. Transcriptomic and lipid metabolism analysis of murine SCs following injury of sural nerves revealed down-regulation of lipogenic genes and regulator of lipid metabolism, including Pparg (peroxisome proliferator-activated receptor gamma) and S1P (sphingosine-1-phosphate). Human SCs failed to induce similar adaptations following ex vivo nerve injury. Pharmacological PPARg and S1P stimulation in mice resulted in up-regulation of lipid gene expression, suggesting a role in SCs switching towards a myelinating state. Altogether, our results suggest that murine SC switching towards a repair state is accompanied by transcriptome and lipidome adaptations, which are reduced in humans.

Background: The neural crest is a group of multipotent cells that give rise to a wide variety of cells, especially portion of the peripheral nervous system. Neural crest cells (NCCs) show evolutionary conserved fate restrictions based on their axial level of origin: cranial, vagal, trunk, and sacral. While much is known about these cells in mammals, birds, amphibians, and fish, relatively little is known in other types of amniotes such as snakes, lizards, and turtles. We attempt here to provide a more detailed description of the early phase of trunk neural crest cell (tNCC) development in turtle embryos., Results: In this study, we show, for the first time, migrating tNCC in the pharyngula embryo of Trachemys scripta by vital-labeling the NCC with DiI and through immunofluorescence. We found that (a) tNCC form a line along the sides of the trunk NT; (b) The presence of late migrating tNCC on the medial portion of the somite; (c) The presence of lateral mesodermal migrating tNCC in pharyngula embryos; (d) That turtle embryos have large/thick peripheral nerves., Conclusions: The similarities and differences in tNCC migration and early PNS development that we observe across sauropsids (birds, snake, gecko, and turtle) suggests that these species evolved some distinct NCC pathways., (© 2019 Wiley Periodicals, Inc.)

Sensory placodes and neural crest cells are among the key cell populations that facilitated the emergence and diversification of vertebrates throughout evolution. Together, they generate the sensory nervous system in the head: both form the cranial sensory ganglia, while placodal cells make major contributions to the sense organs-the eye, ear and olfactory epithelium. Both are instrumental for integrating craniofacial organs and have been key to drive the concentration of sensory structures in the vertebrate head allowing the emergence of active and predatory life forms. Whereas the gene regulatory networks that control neural crest cell development have been studied extensively, the signals and downstream transcriptional events that regulate placode formation and diversity are only beginning to be uncovered. Both cell populations are derived from the embryonic ectoderm, which also generates the central nervous system and the epidermis, and recent evidence suggests that their initial specification involves a common molecular mechanism before definitive neural, neural crest and placodal lineages are established. In this review, we will first discuss the transcriptional networks that pattern the embryonic ectoderm and establish these three cell fates with emphasis on sensory placodes. Second, we will focus on how sensory placode precursors diversify using the specification of otic-epibranchial progenitors and their segregation as an example., (© 2020 Elsevier Inc. All rights reserved.)

Several decades of intense research provided us with a grand framework describing the emergence of neurons in central (CNS) and peripheral (PNS) nervous systems. However, the specifics of molecular events and lineage control leading to a plethora of neuronal subtypes stayed largely unclear. Today, the advances in single cell omics, sample clearing and 3D-microscopy techniques, brain organoids, and synaptic connectivity tracing enabled systematic and unbiased understanding of neuronal diversity, development, circuitry and cell identity control. Novel technological advancements stimulated the transition from conceptual scheme of neuronal differentiation into precise maps of molecular events leading to the diversity of specific neuronal subtypes in relation to their locations and microenvironment. These high-resolution data opened a set of new questions including how transcriptional and epigenetics states control the proportionality of neuronal subpopulations or what are the evolutionary mechanisms of origin of different neuronal subtypes. In this review, we outline the most recent advancements in our understanding of how the neuronal diversity is generated in CNS and PNS and briefly address the challenges and questions arising in the field of neurogenesis., (Copyright © 2019 The Authors. Published by Elsevier Ltd.. All rights reserved.)

Molecular cross talk between the nervous and vascular systems is necessary to maintain the correct coupling of organ structure and function. Molecular pathways shared by both systems are emerging as major players in the communication of the neuronal compartment with the endothelium. Here we review different aspects of this cross talk and how vessels influence the development and homeostasis of the nervous system. Beyond the classical role of the vasculature as a conduit to deliver oxygen and metabolites needed for the energy-demanding neuronal compartment, vessels emerge as powerful signaling systems that control and instruct a variety of cellular processes during the development of neurons and glia, such as migration, differentiation, and structural connectivity. Moreover, a broad spectrum of mild to severe vascular dysfunctions occur in various pathologies of the nervous system, suggesting that mild structural and functional changes at the neurovascular interface may underlie cognitive decline in many of these pathological conditions.

The central and peripheral nervous system (CNS and PNS, respectively) are composed of distinct neuronal and glial cell types with specialized functional properties. However, a small number of select cells traverse the CNS-PNS boundary and connect these two major subdivisions of the nervous system. This pattern of segregation and selective connectivity is established during embryonic development, when neurons and glia migrate to their destinations and axons project to their targets. Here, we provide an overview of the cellular and molecular mechanisms that control cell migration and axon guidance at the vertebrate CNS-PNS border. We highlight recent advances on how cell bodies and axons are instructed to either cross or respect this boundary, and present open questions concerning the development and plasticity of the CNS-PNS interface., (Copyright © 2019 The Authors, some rights reserved; exclusive licensee American Association for the Advancement of Science. No claim to original U.S. Government Works.)

A membrane skeletal molecular complex, protein 4.1G-membrane palmitoylated protein 6 (MPP6)-Lin7-cell adhesion molecule 4 (CADM4), is incorporated in Schwann cells, especially in Schmidt-Lanterman incisures (SLIs), in the mouse peripheral nervous system (PNS). MPP6, Lin7, and CADM4 are transported to SLIs by 4.1G. In this study, we created MPP6-deficient mice and evaluated myelin structure and MPP6 protein complexes. In SLIs in MPP6-deficient nerves, Lin7 was rarely detected by immunohistochemistry and western blotting, but the localization and amount of CADM4 and 4.1G were not altered. Motor activity was not significantly impaired in a tail-suspension test, but the sciatic nerves of MPP6-deficient mice had thicker myelin in internodes by electron microscopy compared to that of wild-type mice. These results indicate that the MPP6-Lin7 complex regulates myelin formation.

Olfactory ensheathing cells (OECs) are often described as being present in both the peripheral and the central nervous systems (PNS and CNS). Furthermore, the olfactory nervous system glia limitans (the glial layer defining the PNS-CNS border) is considered unique as it consists of intermingling OECs and astrocytes. In contrast, the glia limitans of the rest of the nervous system consists solely of astrocytes which create a distinct barrier to Schwann cells (peripheral glia). The ability of OECs to interact with astrocytes is one reason why OECs are believed to be superior to Schwann cells for transplantation therapies to treat CNS injuries. We have used transgenic reporter mice in which glial cells express DsRed fluorescent protein to study the cellular constituents of the glia limitans. We found that the glia limitans layer of the olfactory nervous system is morphologically similar to elsewhere in the nervous system, with a similar low degree of intermingling between peripheral glia and astrocytes. We found that the astrocytic layer of the olfactory bulb is a distinct barrier to bacterial infection, suggesting that this layer constitutes the PNS-CNS immunological barrier. We also found that OECs interact with astrocytes in a similar fashion as Schwann cells in vitro. When cultured in three dimensions, however, there were subtle differences between OECs and Schwann cells in their interactions with astrocytes. We therefore suggest that glial fibrillary acidic protein-reactive astrocyte layer of the olfactory bulb constitutes the glia limitans of the olfactory nervous system and that OECs are primarily "PNS glia.", (© 2018 Wiley Periodicals, Inc.)

Diabetic peripheral neuropathy (DPN) is estimated to affect 50% of diabetic patients. Although DPN is highly prevalent, molecular mechanisms remain unknown and treatment is limited to pain relief and glycemic control. We provide a novel model of acute DPN in zebrafish ( Danio rerio) larvae. Beginning 5 days postfertilization (dpf), zebrafish expressing nitroreductase in their pancreatic β-cells were treated with metronidazole (MTZ) for 48 h and checked for β-cell ablation 7 dpf. In experimental design, this was meant to serve as proof of concept that β-cell ablation and hyperglycemia are possible at this time point, but we were surprised to find changes in both sensory and motor nerve components. Compared with controls, neurod + sensory neurons were often observed outside the dorsal root ganglia in MTZ-treated fish. Fewer motor nerves were properly ensheathed by nkx2.2a + perineurial cells, and tight junctions were disrupted along the motor nerve in MTZ-treated fish compared with controls. Not surprisingly, the motor axons of the MTZ-treated group were defasciculated compared with the control group, myelination was attenuated, and there was a subtle difference in Schwann cell number between the MTZ-treated and control group. All structural changes occurred in the absence of behavioral changes in the larvae at this time point, suggesting that peripheral nerves are influenced by acute hyperglycemia before becoming symptomatic. Moving forward, this novel animal model of DPN will allow us to access the molecular mechanisms associated with the acute changes in the hyperglycemic peripheral nervous system, which may help direct therapeutic approaches.

α-CGRP is synthesized by sensory nerves in the dermis and its release can cause vasodilation and local inflammation. Its vasorelaxant effects are based on the direct activation of smooth muscle and endothelial cells, as well as the activation of mast cells causing the release of vasoactive and proinflammatory mediators. Here, we show that in the capsaicin model for neurogenic inflammation, capsaicin-induced edema formation is mediated by α-CGRP and mast cells, but is absent in thromboxane receptor-deficient mice. Capsaicin treatment of mice induced a thromboxane synthesis, which was mediated by α-CGRP and mast cells. Fittingly, α-CGRP induced thromboxane synthesis in mast cells and the thromboxane receptor agonist I-BOP caused edema formation independently of mast cells, suggesting that mast cells are the source of thromboxane. Most importantly, I-BOP-induced edema formation was mediated by α-CGRP and I-BOP was able to stimulate through calcineurin the α-CGRP release from peripheral neurons. Likewise, the signaling pathway, including α-CGRP, thromboxane receptor, and mast cells, also mediated capsaicin-induced mechanical hypersensitivity, a common symptom of capsaicin treatment. Taken together, the thromboxane-induced α-CGRP release from neurons forms a positive feedback loop causing prolonged α-CGRP release and edema formation during capsaicin-induced neurogenic inflammation., (Copyright © 2018 The Authors. Published by Elsevier Inc. All rights reserved.)

The nervous systems in most bilaterians are centralized, composed of central nervous systems (CNS) and peripheral nervous systems (PNS). Common molecular and cellular patterns of medial nerve cords have been observed in various distantly related bilaterians, suggesting deep homology of CNS. The development patterns of PNS, however, are more diverse than CNS across different phylogenetic lineages and the evolution of PNS so far has been thought to be polygenic. The molecular and cellular programs during the development of PNS among different bilaterian branches are drastically different. For example, vertebrate PNS is essentially derived from neural crest cells and placodes, which are largely vertebrate innovations and do not exist in invertebrates. On the other hand, the lack of common precursor cell types does not necessarily lead to the conclusion of different evolutionary origins. Homology needs to be examined with a deeper and broader scope. In this review, we examined the molecular, cellular and developmental characteristics of PNS in a broad range of bilaterians to summarize our current understanding of variation and potentially conserved themes. These comparisons demonstrate that there exist both migratory and non-migratory neuroblasts in the lateral border of CNS precursors in most model bilaterian animals. These lateral border neuroblasts are specified by conserved gene regulatory network and give rise to sensory neurons, suggesting that lateral border neuroblasts represent the progenitor of PNS and share deep homology among different branches of Bilateria. Future studies are needed to elucidate the evo-devo mechanisms of the lateral neural borders as PNS progenitors., (© 2018 Japanese Society of Developmental Biologists.)

At the cellular level, α-tubulin acetylation alters the structure of microtubules to render them mechanically resistant to compressive forces. How this biochemical property of microtubule acetylation relates to mechanosensation remains unknown, although prior studies have shown that microtubule acetylation influences touch perception. Here, we identify the major Drosophila α-tubulin acetylase (dTAT) and show that it plays key roles in several forms of mechanosensation. dTAT is highly expressed in the larval peripheral nervous system (PNS), but it is largely dispensable for neuronal morphogenesis. Mutation of the acetylase gene or the K40 acetylation site in α-tubulin impairs mechanical sensitivity in sensory neurons and behavioral responses to gentle touch, harsh touch, gravity, and vibration stimuli, but not noxious thermal stimulus. Finally, we show that dTAT is required for mechanically induced activation of NOMPC, a microtubule-associated transient receptor potential channel, and functions to maintain integrity of the microtubule cytoskeleton in response to mechanical stimulation., (Copyright © 2018 The Authors. Published by Elsevier Inc. All rights reserved.)

Following CNS demyelination, oligodendrocyte progenitor cells (OPCs) are able to differentiate into either remyelinating oligodendrocytes (OLs) or remyelinating Schwann cells (SCs). However, the signals that determine which type of remyelinating cell is generated and the underlying mechanisms involved have not been identified. Here, we show that distinctive microenvironments created in discrete niches within demyelinated white matter determine fate decisions of adult OPCs. By comparative transcriptome profiling we demonstrate that an ectopic, injury-induced perivascular niche is enriched with secreted ligands of the BMP and Wnt signalling pathways, produced by activated OPCs and endothelium, whereas reactive astrocyte within non-vascular area express the dual BMP/Wnt antagonist Sostdc1. The balance of BMP/Wnt signalling network is instructive for OPCs to undertake fate decision shortly after their activation: disruption of the OPCs homeostasis during demyelination results in BMP4 upregulation, which, in the absence of Socstdc1, favours SCs differentiation., Competing Interests: JU, JM, CZ, KK, BK, HP, LB, BK, RF, MZ No competing interests declared, (© 2018, Ulanska-Poutanen et al.)

RNA-binding proteins Lin28a/b regulate cellular growth and tissue regeneration. Here, we investigated the role of Lin28 in the control of axon regeneration in postmitotic neurons. We find that Lin28a/b are both necessary and sufficient for supporting axon regeneration in mature sensory neurons through their regulatory partners, let-7 microRNAs (miRNAs). More importantly, overexpression of Lin28a in mature retinal ganglion cells (RGCs) produces robust and sustained optic nerve regeneration. Additionally, combined overexpression of Lin28a and downregulation of Pten in RGCs act additively to promote optic nerve regeneration, potentially by reducing the backward turning of regenerating RGC axons. Our findings not only reveal a vital role of Lin28 signaling in regulating mammalian axon regeneration but also identify a signaling pathway that can promote axon regeneration in the central nervous system (CNS)., (Copyright © 2018 The Author(s). Published by Elsevier Inc. All rights reserved.)

Members of the fibroblast growth factor (FGF) family are involved in a variety of cellular processes. In the nervous system, they affect the differentiation and migration of neurons, the formation and maturation of synapses, and the repair of neuronal circuits following insults. Because of the varied yet critical functions of FGF ligands, their availability and activity must be tightly regulated for the nervous system, as well as other tissues, to properly develop and function in adulthood. In this regard, FGF binding proteins (FGFBPs) have emerged as strong candidates for modulating the actions of secreted FGFs in neural and non-neural tissues. Here, we will review the roles of FGFBPs in the peripheral and central nervous systems., (Copyright © 2018 Elsevier B.V. All rights reserved.)

Background: In the peripheral nervous system (PNS), specialized glial cells called Schwann cells produce myelin, a lipid-rich insulating sheath that surrounds axons and promotes rapid action potential propagation. During development, Schwann cells must undergo extensive cytoskeletal rearrangements in order to become mature, myelinating Schwann cells. The intracellular mechanisms that drive Schwann cell development, myelination, and accompanying cell shape changes are poorly understood., Methods: Through a forward genetic screen in zebrafish, we identified a mutation in the atypical guanine nucleotide exchange factor, dock1, that results in decreased myelination of peripheral axons. Rescue experiments and complementation tests with newly engineered alleles confirmed that mutations in dock1 cause defects in myelination of the PNS. Whole mount in situ hybridization, transmission electron microscopy, and live imaging were used to fully define mutant phenotypes., Results: We show that Schwann cells in dock1 mutants can appropriately migrate and are not decreased in number, but exhibit delayed radial sorting and decreased myelination during early stages of development., Conclusions: Together, our results demonstrate that mutations in dock1 result in defects in Schwann cell development and myelination. Specifically, loss of dock1 delays radial sorting and myelination of peripheral axons in zebrafish.

Adult peripheral nerves in vertebrates can regrow their axons and re-establish function after crush lesion. However, when there is extensive loss of a nerve segment, due to an accident or compressive damage caused by tumors, regeneration is strongly impaired. In order to overcome this problem, bioengineering strategies have been employed, using biomaterials formed by key cell types combined with biodegradable polymers. Many of these strategies are successful, and regenerated nerve tissue can be observed 12 weeks after the implantation. Mesenchymal stem cells (MSCs) are one of the key cell types and the main stem-cell population experimentally employed for cell therapy and tissue engineering of peripheral nerves. The ability of these cells to release a range of different small molecules, such as neurotrophins, growth factors and interleukins, has been widely described and is a feasible explanation for the improvement of nerve regeneration. Moreover, the multipotent capacity of MSCs has been very often challenged with demonstrations of pluripotency, which includes differentiation into any neural cell type. In this study, we generated a biomaterial formed by EGFP-MSCs, constitutively covering microstructured filaments made of poly-ε-caprolactone. This biomaterial was implanted in the sciatic nerve of adult rats, replacing a 12-mm segment, inside a silicon tube. Our results showed that six weeks after implantation, the MSCs had differentiated into connective-tissue cells, but not into neural crest-derived cells such as Schwann cells. Together, present findings demonstrated that MSCs can contribute to nerve-tissue regeneration, producing trophic factors and differentiating into fibroblasts, endothelial and smooth-muscle cells, which compose the connective tissue.

Heterotopic ossification (HO), or de novo bone formation in soft tissue, is often observed following traumatic injury. Recent studies suggest that peripheral nerves may play a key functional role in this process. The results supporting a neurological basis for HO are examined in this article. Evidence supports the fact that BMPs released from bone matrix possess the capacity to induce HO. However, the process cannot be recapitulated using recombinant proteins without extremely high doses suggesting other components are required for this process. Study of injuries that increase risk for HO, i.e. amputation, hip replacement, elbow fracture, burn, and CNS injury suggests that a likely candidate is traumatic injury of adjacent peripheral nerves. Recent studies suggest neuroinflammation may play a key functional role, by its ability to open the blood-nerve barrier (BNB). Barrier opening is characterized by a change in permeability and is experimentally assessed by the ability of Evans blue dye to enter the endoneurium of peripheral nerves. A combination of BMP and barrier opening is required to activate bone progenitors in the endoneurial compartment. This process is referred to as "neurogenic HO"., (Copyright © 2017 Elsevier Inc. All rights reserved.)

Physical and chemical cues from the environment are used to direct animal behavior through a complex network of connections originating in exteroceptors. In chordates, mechanosensory and chemosensory neurons of the peripheral nervous system (PNS) must signal to the motor circuits of the central nervous system (CNS) through a series of pathways that integrate and regulate the output to motor neurons (MN); ultimately these drive contraction of the tail and limb muscles. We used serial-section electron microscopy to reconstruct PNS neurons and their hitherto unknown synaptic networks in the tadpole larva of a sibling chordate, the ascidian, Ciona intestinalis. The larva has groups of neurons in its apical papillae, epidermal neurons in the rostral and apical trunk, caudal neurons in the dorsal and ventral epidermis, and a single tail tip neuron. The connectome reveals that the PNS input arises from scattered groups of these epidermal neurons, 54 in total, and has three main centers of integration in the CNS: in the anterior brain vesicle (which additionally receives input from photoreceptors of the ocellus), the motor ganglion (which contains five pairs of MN), and the tail, all of which in turn are themselves interconnected through important functional relay neurons. Some neurons have long collaterals that form autapses. Our study reveals interconnections with other sensory systems, and the exact inputs to the motor system required to regulate contractions in the tail that underlie larval swimming, or to the CNS to regulate substrate preference prior to the induction of larval settlement and metamorphosis., (© 2017 Wiley Periodicals, Inc.)

Neural stem cells (NSCs) often give rise to a mixed population of cells during differentiation. However, the dynamical origin of these mixed states is poorly understood. In this article, our mathematical modeling study demonstrates that the bone morphogenetic protein 2 (BMP2) mediated disparate differentiation dynamics of NSCs in central and peripheral nervous systems essentially function through two distinct bistable switches that are mutually interconnected via a mushroom-like bifurcation. Stochastic simulations of the model reveal that the mixed population originates due to the existence of these bistable switching regulations and that the maintenance of such mixed states depends on the level of stochastic fluctuations of the system. It further demonstrates that due to extrinsic variability, cells in an NSC population can dynamically transit from mushroom to a unique isola kind of bifurcation state, which essentially extends the range of the BMP2-driven mixed population state during differentiation. Importantly, the model predicts that by individually altering the expression level of key regulatory proteins, the NSCs can be converted entirely to a preferred phenotype for BMP2 doses that previously resulted in a mixed population. Our findings show that efficient neuronal regeneration can be achieved by systematically maneuvering the differentiation dynamics., (Copyright © 2018 Biophysical Society. Published by Elsevier Inc. All rights reserved.)

During brainstem development, newborn neurons originating from the rhombic lip embark on exceptionally long migrations to generate nuclei important for audition, movement, and respiration. Along the way, this highly motile population passes several cranial nerves yet remains confined to the CNS. We found that Ntn1 accumulates beneath the pial surface separating the CNS from the PNS, with gaps at nerve entry sites. In mice null for Ntn1 or its receptor DCC, hindbrain neurons enter cranial nerves and migrate into the periphery. CNS neurons also escape when Ntn1 is selectively lost from the sub-pial region (SPR), and conversely, expression of Ntn1 throughout the mutant hindbrain can prevent their departure. These findings identify a permissive role for Ntn1 in maintaining the CNS-PNS boundary. We propose that Ntn1 confines rhombic lip-derived neurons by providing a preferred substrate for tangentially migrating neurons in the SPR, preventing their entry into nerve roots., (Copyright © 2018 The Author(s). Published by Elsevier Inc. All rights reserved.)

Objective: Nerves in the peripheral nervous system (PNS) contain axons with specific motor, somatosensory and autonomic functions. Optogenetics offers an efficient approach to selectively activate axons within the nerve. However, the heterogeneous nature of nerves and their tortuous route through the body create a challenging environment to reliably implant a light delivery interface., Approach: Here, we propose an optical peripheral nerve interface-an optocuff-, so that optogenetic modulation of peripheral nerves become possible in freely behaving mice., Main Results: Using this optocuff, we demonstrate orderly recruitment of motor units with epineural optical stimulation of genetically targeted sciatic nerve axons, both in anaesthetized and in awake, freely behaving animals. Behavioural experiments and histology show the optocuff does not damage the nerve thus is suitable for long-term experiments., Significance: These results suggest that the soft optocuff might be a straightforward and efficient tool to support more extensive study of the PNS using optogenetics.

During the development of the central nervous system (CNS), only motor axons project into peripheral nerves. Little is known about the cellular and molecular mechanisms that control the development of a boundary at the CNS surface and prevent CNS neuron emigration from the neural tube. It has previously been shown that a subset of spinal cord commissural axons abnormally invades sensory nerves in Ntn1 hypomorphic embryos and Dcc knockouts. However, whether netrin 1 also plays a similar role in the brain is unknown. In the hindbrain, precerebellar neurons migrate tangentially under the pial surface, and their ventral migration is guided by netrin 1. Here, we show that pontine neurons and inferior olivary neurons, two types of precerebellar neurons, are not confined to the CNS in Ntn1 and Dcc mutant mice, but that they invade the trigeminal, auditory and vagus nerves. Using a Ntn1 conditional knockout, we show that netrin 1, which is released at the pial surface by ventricular zone progenitors is responsible for the CNS confinement of precerebellar neurons. We propose, that netrin 1 distribution sculpts the CNS boundary by keeping CNS neurons in netrin 1-rich domains., Competing Interests: Competing interestsThe authors declare no competing or financial interests., (© 2018. Published by The Company of Biologists Ltd.)

The dorsal root ganglia (DRG) consist of a multitude of sensory neuronal subtypes that function to relay sensory stimuli, including temperature, pressure, pain and position to the central nervous system. Our knowledge of DRG sensory neurons have been predominantly driven by animal studies and considerably less is known about the human DRG. Human embryonic stem cells (hESC) are valuable resource to help close this gap. Our previous studies reported an efficient system for deriving neural crest and DRG sensory neurons from hESC. Here we show that this differentiation system gives rise to heterogeneous populations of sensory neuronal subtypes as demonstrated by phenotypic and functional analyses. Furthermore, using microelectrode arrays the maturation rate of the hESC-derived sensory neuronal cultures was monitored over 8 weeks in culture, showing their spontaneous firing activities starting at about 12 days post-differentiation and reaching maximum firing at about 6 weeks. These studies are highly valuable for developing an in vitro platform to study the diversity of sensory neuronal subtypes found within the human DRG.

Schwann cells are the main glial cells of the peripheral nervous system (PNS) and play key roles in peripheral nerve development and function, including providing myelin that is essential for normal movement and sensation in the adult. Schwann cells can be readily destabilized by a wide variety of distinct conditions that range from nerve injury to immune assaults, metabolic disturbances, microbial infections, or genetic defects, leading to the breakdown of myelin (demyelination) and a subsequent switch in phenotypic states. This striking feature of Schwann cells forms the cornerstone of several debilitating and even fatal PNS neurological disorders that include the demyelinating neuropathies Guillain Barré syndrome (GBS) and Charcot-Marie-Tooth disease (CMT), and PNS cancers, including Neurofibromatosis.Primary Schwann cell cultures have proved a valuable tool to dissect key mechanisms that regulate proliferation, survival, differentiation, and myelination of these glial cell types. In this chapter, we describe the steps involved in the isolation and purification of Schwann cells from rodent peripheral nerves and the use of these cultures to model myelination in vitro.

Nerve injury is a large problem that produces much pain in patients. Injury to the nervous system causes serious consequences and affects a person's quality of life. The development of tissue engineering has created a brighter future for nerve regeneration, and research has not stopped since the discovery of stem cells. Stem cells are a type of pluripotent cell that exhibits the capacity of selfdifferentiation and proliferation. Many studies have demonstrated the ability of stem cells to differentiate into other types of cells, including neurons, after induction with trophic factors in vivo and in vitro. Scientists have isolated a variety of stem cells from different organs and tissues in the human body and demonstrated that these cells were efficacious in regenerative medicine. The use of these cells provides a non-surgical method for the treatment of neurological diseases, such as nerve defects. However, many problems must be resolved before using these cells in the clinical field. The microenvironment and delivery methods of cells also affect the regeneration process. The present article comprehensively summarizes the progress of stem cells in the field of nerve regeneration in the recent decades., (Copyright© Bentham Science Publishers; For any queries, please email at epub@benthamscience.org.)

Activation of caspases is an essential step toward initiating apoptotic cell death. During metamorphosis of Drosophila melanogaster, many larval neurons are programmed for elimination to establish an adult central nervous system (CNS) as well as peripheral nervous system (PNS). However, their neuronal functions have remained mostly unknown due to the lack of proper tools to identify them. To obtain detailed information about the neurochemical phenotypes of the doomed larval neurons and their timing of death, we generated a new GFP-based caspase sensor (Casor) that is designed to change its subcellular position from the cell membrane to the nucleus following proteolytic cleavage by active caspases. Ectopic expression of Casor in vCrz and bursicon, two different peptidergic neuronal groups that had been well-characterized for their metamorphic programmed cell death, showed clear nuclear translocation of Casor in a caspase-dependent manner before their death. We found similar events in some cholinergic neurons from both CNS and PNS. Moreover, Casor also reported significant caspase activities in the ventral and dorsal common excitatory larval motoneurons shortly after puparium formation. These motoneurons were previously unknown for their apoptotic fate. Unlike the events seen in the neurons, expression of Casor in non-neuronal cell types, such as glial cells and S2 cells, resulted in the formation of cytoplasmic aggregates, preventing its use as a caspase sensor in these cell types. Nonetheless, our results support Casor as a valuable molecular tool not only for identifying novel groups of neurons that become caspase-active during metamorphosis but also for monitoring developmental timing and cytological changes within the dying neurons.

Biomaterials can be utilized to assist in the transplantation of Schwann cells to the central and peripheral nervous system. The biomaterials can be natural or man-made, and can have preformed shapes or injectable formats. Biomaterials can play multiple roles in cellular transplantation; for example, they can assist with cellular integration and protect Schwann cells from cell death initiated by the lack of a substrate, an occurrence known as "anoikis." In addition, biomaterials can be engineered to increase cell proliferation and differentiation by the addition of ligands bound to the substrate. Here, we describe the incorporation of Schwann cells to both man-made and natural matrices for in vitro and in vivo measures relevant to Schwann cell transplantation strategies.

Modeling myelination in vitro allows mechanistic study of developmental myelination and short-term myelin maintenance, but analyses possible to carry out using currently available models are usually limited because of high cell density and the lack of separation between neurons and myelinating cells. Furthermore, regeneration studies of myelinated systems after lesion require compartmentalization of neuronal cell bodies, axons, and myelinating cells. Here we describe a compartmentalized method using microfluidics that allows live-cell imaging at the single-cell level to follow short- and long-term dynamic interactions of neurons and myelinating cells and large-scale analyses, e.g., RNA sequencing on pure or highly enriched neurons or myelinating cells, separately.

Peripheral glia includes predominantly myelinating and non-myelinating Schwann cells in addition to satellite, terminal and enteric glia as well as other unresolved subtypes with localized functions. Of these subtypes, all of them originate from neural crest-derived embryonic Schwann cell precursors (SCPs). Specific gene regulatory networks control neural crest specification and downstream events, including SCP differentiation and myelination. Embryonic SCPs are multipotent and generate neuroendocrine cells, parasympathetic and enteric neurons, melanocytes and other cell types. The evolutionary origin of peripheral Schwann cell lineage is not widely discussed in the literature, despite numerous similarities between central and peripheral glia. Here, we review the major features of the Schwann cell lineage and proceed to an evolutionary discussion around possible relations between central and peripheral glial cells., (Copyright © 2017 The Authors. Published by Elsevier Ltd.. All rights reserved.)

Broad plasticity of the peripheral glia is an emerging concept during development of the peripheral nervous system (PNS). Recent studies have identified the neural crest-derived boundary caps (BCs), as a multitask stem cell population of the developing PNS. BC progeny migrate along the nerves to provide the major glial component of nerve roots and nerve terminals in the skin. Strikingly, those two locations constitute the privileged sites for development of benign peripheral nerve sheath tumors called neurofibromas in patients with neurofibromatosis type 1 (NF1), making BCs attractive candidates for the 'cell of origin' of this disease. Here, we review these exciting findings, focusing on the origin and novel functions of BCs. We further discuss the heterogeneity of BCs, and address their implication in the pathogenesis of NF1., (Copyright © 2017 Elsevier Ltd. All rights reserved.)

Myelination is a biosynthetically demanding process in which mTORC1, the gatekeeper of anabolism, occupies a privileged regulatory position. We have shown previously that loss of mTORC1 function in Schwann cells (SCs) hampers myelination. Here, we genetically disrupted key inhibitory components upstream of mTORC1, TSC1 or PTEN, in mouse SC development, adult homeostasis, and nerve injury. Surprisingly, the resulting mTORC1 hyperactivity led to markedly delayed onset of both developmental myelination and remyelination after injury. However, if mTORC1 was hyperactivated after myelination onset, radial hypermyelination was observed. At early developmental stages, physiologically high PI3K-Akt-mTORC1 signaling suppresses expression of Krox20 (Egr2), the master regulator of PNS myelination. This effect is mediated by S6K and contributes to control mechanisms that keep SCs in a not-fully differentiated state to ensure proper timing of myelination initiation. An ensuing decline in mTORC1 activity is crucial to allow myelination to start, while remaining mTORC1 activity drives myelin growth.

Numerous studies have shown that the intrinsic axonal regenerative capacity of neurons differs between the peripheral and central nervous systems (CNSs). However, the molecular mechanisms controlling intrinsic axonal regenerative capacity are unclear. A better understanding of these mechanisms should aid in the development of effective therapeutic strategies for traumatic nervous system injury, including spinal cord injury. Here, we found that blocking mammalian target of rapamycin (mTOR) activity dramatically diminished axonal regrowth from embryonic cortical neurons. However, mTOR activity was not required for axonal regrowth from adult peripheral sensory neurons. By analyzing the levels of phospho-S6, a downstream target of mTOR, we found that embryonic cortical neurons had a much higher mTOR activity compared with adult peripheral sensory neurons. Our findings suggest that, in the CNS, the mTOR pathway plays a critical role in regulating the regenerative capacity of neurons, in contrast to the peripheral nervous system., (© The Author 2017. Published by Oxford University Press on behalf of the Institute of Biochemistry and Cell Biology, Shanghai Institutes for Biological Sciences, Chinese Academy of Sciences. All rights reserved. For permissions, please e-mail: journals.permissions@oup.com.)

The lateral neural plate border (NPB), the neural part of the vertebrate neural border, is composed of central nervous system (CNS) progenitors and peripheral nervous system (PNS) progenitors. In invertebrates, PNS progenitors are also juxtaposed to the lateral boundary of the CNS. Whether there are conserved molecular mechanisms determining vertebrate and invertebrate lateral neural borders remains unclear. Using single-cell-resolution gene-expression profiling and genetic analysis, we present evidence that orthologs of the NPB specification module specify the invertebrate lateral neural border, which is composed of CNS and PNS progenitors. First, like in vertebrates, the conserved neuroectoderm lateral border specifier Msx/vab-15 specifies lateral neuroblasts in Caenorhabditis elegans Second, orthologs of the vertebrate NPB specification module ( Msx/vab-15 , Pax3/7/pax-3 , and Zic/ref-2 ) are significantly enriched in worm lateral neuroblasts. In addition, like in other bilaterians, the expression domain of Msx/vab-15 is more lateral than those of Pax3/7/pax-3 and Zic/ref- 2 in C. elegans Third, we show that Msx/vab-15 regulates the development of mechanosensory neurons derived from lateral neural progenitors in multiple invertebrate species, including C. elegans , Drosophila melanogaster , and Ciona intestinalis We also identify a novel lateral neural border specifier, ZNF703/tlp-1 , which functions synergistically with Msx/vab- 15 in both C. elegans and Xenopus laevis These data suggest a common origin of the molecular mechanism specifying lateral neural borders across bilaterians., Competing Interests: The authors declare no conflict of interest.

See Saporta and Shy (doi:10.1093/awx048) for a scientific commentary on this article.Effective bidirectional signalling between axons and Schwann cells is essential for both the development and maintenance of peripheral nerve function. We have established conditions by which human induced pluripotent stem cell-derived sensory neurons can be cultured with rat Schwann cells, and have produced for the first time long-term and stable myelinating co-cultures with human neurons. These cultures contain the specialized domains formed by axonal interaction with myelinating Schwann cells, such as clustered voltage-gated sodium channels at the node of Ranvier and Shaker-type potassium channel (Kv1.2) at the juxtaparanode. Expression of type III neuregulin-1 (TIIINRG1) in induced pluripotent stem cell-derived sensory neurons strongly enhances myelination, while conversely pharmacological blockade of the NRG1-ErbB pathway prevents myelination, providing direct evidence for the ability of this pathway to promote the myelination of human sensory axons. The β-secretase, BACE1 is a protease needed to generate active NRG1 from the full-length form. Due to the fact that it also cleaves amyloid precursor protein, BACE1 is a therapeutic target in Alzheimer's disease, however, consistent with its role in NRG1 processing we find that BACE1 inhibition significantly impairs myelination in our co-culture system. In order to exploit co-cultures to address other clinically relevant problems, they were exposed to anti-disialosyl ganglioside antibodies, including those derived from a patient with a sensory predominant, inflammatory neuropathy with mixed axonal and demyelinating electrophysiology. The co-cultures reveal that both mouse and human disialosyl antibodies target the nodal axolemma, induce acute axonal degeneration in the presence of complement, and impair myelination. The human, neuropathy-associated IgM antibody is also shown to induce complement-independent demyelination. Myelinating co-cultures using human induced pluripotent stem cell-derived sensory neurons thus provide insights into the cellular and molecular specialization of axoglial signalling, how pharmacological agents may promote or impede such signalling and the pathogenic effects of ganglioside antibodies.awx012media15372351982001., (© The Author (2017). Published by Oxford University Press on behalf of the Guarantors of Brain.)

Adhesion G protein-coupled receptors (aGPCRs) are a large family of transmembrane proteins that play important roles in many processes during development, primarily through cell-cell and cell-extracellular matrix (ECM) interactions. In the nervous system, they have been linked to the complex process of myelination, both in the central and peripheral nervous system. GPR126 is essential in Schwann cell-mediated myelination in the peripheral nervous system (PNS), while GPR56 is involved in oligodendrocyte development central nervous system (CNS) myelination. VLGR1 is another aGPCR that is associated with the expression of myelin-associated glycoprotein (MAG) which has inhibitory effects on the process of nerve repair. The ECM is composed of a vast array of structural proteins, three of which interact specifically with aGPCRs: collagen III/GPR56, collagen IV/GPR126, and laminin-211/GPR126. As druggable targets, aGPCRs are valuable in their ability to unlock treatment for a wide variety of currently debilitating myelin disorders. Developmental Dynamics 246:275-284, 2017. © 2016 Wiley Periodicals, Inc., (© 2016 Wiley Periodicals, Inc.)

Generating a precise cellular and molecular cartography of the human embryo is essential to our understanding of the mechanisms of organogenesis in normal and pathological conditions. Here, we have combined whole-mount immunostaining, 3DISCO clearing, and light-sheet imaging to start building a 3D cellular map of the human development during the first trimester of gestation. We provide high-resolution 3D images of the developing peripheral nervous, muscular, vascular, cardiopulmonary, and urogenital systems. We found that the adult-like pattern of skin innervation is established before the end of the first trimester, showing important intra- and inter-individual variations in nerve branches. We also present evidence for a differential vascularization of the male and female genital tracts concomitant with sex determination. This work paves the way for a cellular and molecular reference atlas of human cells, which will be of paramount importance to understanding human development in health and disease. PAPERCLIP., (Copyright © 2017 Elsevier Inc. All rights reserved.)

Glutaryl-CoA dehydrogenase (GCDH) is a mitochondrial enzyme that is involved in the degradation of tryptophan, lysine and hydroxylysine. Deficient enzyme activity leads to glutaric aciduria type-I (GA-I). This neurometabolic disease usually manifests with acute encephalopathic crises and striatal neuronal death in early childhood leading to an irreversible dystonic-dyskinetic movement disorder. Fronto-temporal atrophy and white matter changes are already present in the pre-symptomatic period. No detailed information on GCDH expression during embryonic development and in adulthood was available so far. Using immunofluorescence microscopy and cell-type-specific markers to localize GCDH in different tissues, we describe the differential cellular localization of GCDH in adult rat brain and peripheral organs as well as its spatiotemporal expression pattern. During embryonic development GCDH was predominantly expressed in neurons of the central and peripheral nervous system. Significant expression levels were found in epithelial cells (skin, intestinal and nasal mucosa) of rat embryos at different developmental stages. Besides the expected strong expression in liver, GCDH was found to be significantly expressed in neurons of different brain regions, renal proximal tubules, intestinal mucosa and peripheral nerves of adult rats. GCDH was found widely expressed in embryonic and adult rat tissues. In rat embryos GCDH is predominantly expressed in brain implying an important role for brain development. Interestingly, GCDH was found to be significantly expressed in different other organs (e.g. kidney, gut) in adult rats probably explaining the evolving phenotype in GA-I patients., (Copyright © 2016 IBRO. Published by Elsevier Ltd. All rights reserved.)

In the vertebrate nervous system, the fast conduction of action potentials is potentiated by the myelin sheath, a multi-lamellar, lipid-rich structure that also provides vital trophic and metabolic support to axons. Myelin is elaborated by the plasma membrane of specialized glial cells, oligodendrocytes in the central nervous system (CNS) and Schwann cells (SCs) in the peripheral nervous system (PNS). The diseases that result from damage to myelin or glia, including multiple sclerosis and Charcot-Marie-Tooth disease, underscore the importance of these cells for human health. Therefore, an understanding of glial development and myelination is crucial in addressing the etiology of demyelinating diseases and developing patient therapies. In this review, we discuss new insights into the roles of mechanotransduction and cytoskeletal rearrangements as well as activity dependent myelination and axonal maintenance by glia. Together, these discoveries advance our knowledge of myelin and glia in nervous system health and plasticity throughout life., (Copyright © 2016 Elsevier Ltd. All rights reserved.)