{"title":"What is myelin?","authors":"Daniel K Hartline","doi":"10.1017/S1740925X09990263","DOIUrl":"https://doi.org/10.1017/S1740925X09990263","url":null,"abstract":"<p><p>The evolution of a character is better appreciated if examples of convergent emergence of the same character are available for comparison. Three instances are known among invertebrates of the evolution of axonal sheaths possessing the functional properties and many of the structural properties of vertebrate myelin. Comparison of these invertebrate myelins raises the question of what structural features must a sheath possess in order to produce the two principal functional characteristics of impulse speed enhancement and energy savings. This essay reviews the features recognized by early workers as pertaining to myelin in vertebrate and invertebrate alike: osmiophilia, negative birefringence and saltatory conduction. It then examines common features revealed by the advent of electron microscopy: multiplicity of lipid membranes, condensation of those membranes, specialized marginal seals, and nodes. Next it examines the robustness of these features as essential components of a speed-enhancing sheath. Features that are not entirely essential for speed enhancement include membrane compaction, spiral wrapping of layers, glial cell involvement, non-active axonal membrane, and even nodes and perinodal sealing. This permissiveness is discussed in relation to the possible evolutionary origin of myelin.</p>","PeriodicalId":19153,"journal":{"name":"Neuron glia biology","volume":"4 2","pages":"153-63"},"PeriodicalIF":0.0,"publicationDate":"2008-05-01","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"https://sci-hub-pdf.com/10.1017/S1740925X09990263","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"28389270","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":0,"RegionCategory":"","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
Neuron glia biologyPub Date : 2008-05-01Epub Date: 2009-06-05DOI: 10.1017/S1740925X0900009X
Wiebke Möbius, Julia Patzig, Klaus-Armin Nave, Hauke B Werner
{"title":"Phylogeny of proteolipid proteins: divergence, constraints, and the evolution of novel functions in myelination and neuroprotection.","authors":"Wiebke Möbius, Julia Patzig, Klaus-Armin Nave, Hauke B Werner","doi":"10.1017/S1740925X0900009X","DOIUrl":"https://doi.org/10.1017/S1740925X0900009X","url":null,"abstract":"<p><p>The protein composition of myelin in the central nervous system (CNS) has changed at the evolutionary transition from fish to tetrapods, when a lipid-associated transmembrane-tetraspan (proteolipid protein, PLP) replaced an adhesion protein of the immunoglobulin superfamily (P0) as the most abundant constituent. Here, we review major steps of proteolipid evolution. Three paralog proteolipids (PLP/DM20/DMalpha, M6B/DMgamma and the neuronal glycoprotein M6A/DMbeta) exist in vertebrates from cartilaginous fish to mammals, and one (M6/CG7540) can be traced in invertebrate bilaterians including the planktonic copepod Calanus finmarchicus that possess a functional myelin equivalent. In fish, DMalpha and DMgamma are coexpressed in oligodendrocytes but are not major myelin components. PLP emerged at the root of tetrapods by the acquisition of an enlarged cytoplasmic loop in the evolutionary older DMalpha/DM20. Transgenic experiments in mice suggest that this loop enhances the incorporation of PLP into myelin. The evolutionary recruitment of PLP as the major myelin protein provided oligodendrocytes with the competence to support long-term axonal integrity. We suggest that the molecular shift from P0 to PLP also correlates with the concentration of adhesive forces at the radial component, and that the new balance between membrane adhesion and dynamics was favorable for CNS myelination.</p>","PeriodicalId":19153,"journal":{"name":"Neuron glia biology","volume":"4 2","pages":"111-27"},"PeriodicalIF":0.0,"publicationDate":"2008-05-01","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"https://sci-hub-pdf.com/10.1017/S1740925X0900009X","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"28221923","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":0,"RegionCategory":"","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
Neuron glia biologyPub Date : 2008-05-01Epub Date: 2009-06-10DOI: 10.1017/S1740925X0900012X
Betty I Roots
{"title":"The phylogeny of invertebrates and the evolution of myelin.","authors":"Betty I Roots","doi":"10.1017/S1740925X0900012X","DOIUrl":"https://doi.org/10.1017/S1740925X0900012X","url":null,"abstract":"<p><p>Current concepts of invertebrate phylogeny are reviewed. Annelida and Arthropoda, previously regarded as closely related, are now placed in separate clades. Myelin, a sheath of multiple layers of membranes around nerve axons, is found in members of the Annelida, Arthropoda and Chordata. The structure, composition and function of the sheaths in Annelida and Arthropoda are examined and evidence for the separate evolutionary origins of myelin in the three clades is presented. That myelin has arisen independently at least three times, namely in Annelids, Arthropodas and Chordates, provides a remarkable example of convergent evolution.</p>","PeriodicalId":19153,"journal":{"name":"Neuron glia biology","volume":"4 2","pages":"101-9"},"PeriodicalIF":0.0,"publicationDate":"2008-05-01","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"https://sci-hub-pdf.com/10.1017/S1740925X0900012X","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"28231571","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":0,"RegionCategory":"","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
Daniel A Kirschner, Jothie Karthigesan, Oscar A Bizzozero, Bela Kosaras, Hideyo Inouye
{"title":"Myelin structure and composition of myelinated tissue in the African lungfish.","authors":"Daniel A Kirschner, Jothie Karthigesan, Oscar A Bizzozero, Bela Kosaras, Hideyo Inouye","doi":"10.1017/S1740925X09990196","DOIUrl":"https://doi.org/10.1017/S1740925X09990196","url":null,"abstract":"<p><p>To analyze myelin structure and the composition of myelinated tissue in the African lungfish (Protopterus dolloi), we used a combination of ultrastructural and biochemical techniques. Electron microscopy showed typical multilamellar myelin: CNS sheaths abutted one another, and PNS sheaths were separated by endoneurial collagen. The radial component, prominent in CNS myelin of higher vertebrates, was suggested by the pattern of staining but was poorly organized. The lipid and myelin protein compositions of lungfish tissues more closely resembled those of teleost than those of higher vertebrates (frog, mouse). Of particular note, for example, lungfish glycolipids lacked hydroxy fatty acids. Native myelin periodicities from unfixed nerves were in the range of those for higher vertebrates rather than for teleost fish. Lungfish PNS myelin had wider inter-membrane spaces compared with other vertebrates, and lungfish CNS myelin had spaces that were closer in value to those in mammalian than to amphibian or teleost myelins. The membrane lipid bilayer was narrower in lungfish PNS myelin compared to other vertebrates, whereas in the CNS myelin the bilayer was in the typical range. Lungfish PNS myelin showed typical compaction and swelling responses to incubation in acidic or alkaline hypotonic saline. The CNS myelin, by contrast, did not compact in acidic saline but did swell in the alkaline solution. This lability was more similar to that for the higher vertebrates than for teleost.</p>","PeriodicalId":19153,"journal":{"name":"Neuron glia biology","volume":"4 2","pages":"59-70"},"PeriodicalIF":0.0,"publicationDate":"2008-05-01","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"https://sci-hub-pdf.com/10.1017/S1740925X09990196","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"28389266","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":0,"RegionCategory":"","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
Neuron glia biologyPub Date : 2008-02-01Epub Date: 2009-02-27DOI: 10.1017/S1740925X09000064
Alfonso Araque
{"title":"Astrocytes process synaptic information.","authors":"Alfonso Araque","doi":"10.1017/S1740925X09000064","DOIUrl":"https://doi.org/10.1017/S1740925X09000064","url":null,"abstract":"<p><p>Astrocytes were classically considered as simple supportive cells for neurons without a significant role in information processing by the nervous system. However, considerable amounts of evidence obtained by several groups during the past years demonstrated the existence of a bidirectional communication between astrocytes and neurons, which prompted a re-examination of the role of astrocytes in the physiology of the nervous system. While neurons base their excitability on electrical signals generated across the membrane, astrocytes base their cellular excitability on variations of the Ca2+ concentration in the cytosol. This article discusses our current knowledge of the properties of the synaptically evoked astrocyte Ca2+ signal, which reveals that astrocytes display integrative properties for synaptic information processing. Astrocytes respond selectively to different axon pathways, discriminate between the activity of different synapses and their Ca2+ signal is non-linearly modulated by the simultaneous activity of different synaptic inputs. Furthermore, this Ca2+ signal modulation depends on astrocyte cellular intrinsic properties and is bidirectionally regulated by the level of synaptic activity. Finally, astrocyte Ca2+ elevations can trigger the release of gliotransmitters, which modulate neuronal activity as well as synaptic transmission and plasticity, hence granting the bidirectional communication with neurons. Consequently, astrocytes can be considered as cellular elements involved in information processing by the nervous system.</p>","PeriodicalId":19153,"journal":{"name":"Neuron glia biology","volume":"4 1","pages":"3-10"},"PeriodicalIF":0.0,"publicationDate":"2008-02-01","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"https://sci-hub-pdf.com/10.1017/S1740925X09000064","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"28012256","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":0,"RegionCategory":"","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
{"title":"Activity-dependent neuron-glial signaling by ATP and leukemia-inhibitory factor promotes hippocampal glial cell development.","authors":"Jonathan E Cohen, R Douglas Fields","doi":"10.1017/S1740925X09000076","DOIUrl":"10.1017/S1740925X09000076","url":null,"abstract":"<p><p>Activity-dependent signaling between neurons and astrocytes contributes to experience-dependent plasticity and development of the nervous system. However, mechanisms responsible for neuron-glial interactions and the releasable factors that underlie these processes are not well understood. The pro-inflammatory cytokine, leukemia-inhibitory factor (LIF), is transiently expressed postnatally by glial cells in the hippocampus and rapidly up-regulated by enhanced neural activity following seizures. To test the hypothesis that spontaneous neural activity regulates glial development in hippocampus via LIF signaling, we blocked spontaneous activity with the sodium channel blocker tetrodotoxin (TTX) in mixed hippocampal cell cultures in combination with blockers of LIF and purinergic signaling. TTX decreased the number of GFAP-expressing astrocytes in hippocampal cell culture. Furthermore, blocking purinergic signaling by P2Y receptors contributed to reduced numbers of astrocytes. Blocking activity or purinergic signaling in the presence of function-blocking antibodies to LIF did not further decrease the number of astrocytes. Moreover, hippocampal cell cultures prepared from LIF -/- mice had reduced numbers of astrocytes and activity-dependent neuron-glial signaling promoting differentiation of astrocytes was absent. The results show that endogenous LIF is required for normal development of hippocampal astrocytes, and this process is regulated by spontaneous neural impulse activity through the release of ATP.</p>","PeriodicalId":19153,"journal":{"name":"Neuron glia biology","volume":"4 1","pages":"43-55"},"PeriodicalIF":0.0,"publicationDate":"2008-02-01","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"https://www.ncbi.nlm.nih.gov/pmc/articles/PMC2756042/pdf/nihms111403.pdf","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"28106667","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":0,"RegionCategory":"","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"OA","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
Neuron glia biologyPub Date : 2008-02-01Epub Date: 2008-11-13DOI: 10.1017/S1740925X09000015
Xiaoqin Zhu, Robert A Hill, Akiko Nishiyama
{"title":"NG2 cells generate oligodendrocytes and gray matter astrocytes in the spinal cord.","authors":"Xiaoqin Zhu, Robert A Hill, Akiko Nishiyama","doi":"10.1017/S1740925X09000015","DOIUrl":"https://doi.org/10.1017/S1740925X09000015","url":null,"abstract":"<p><p>NG2 cells represent a unique glial cell population that is distributed widely throughout the developing and adult CNS and is distinct from astrocytes, mature oligodendrocytes and microglia. The ability of NG2 cells to differentiate into myelinating oligodendrocytes has been documented in vivo and in vitro. We reported recently that NG2 cells in the forebrain differentiate into myelinating oligodendrocytes but into a subpopulation of protoplasmic astrocytes (Zhu et al., 2008). However, the in vivo fate of NG2 cells in the spinal cord and cerebellum has remained unknown. To investigate the fate of NG2 cells in caudal central nervous system (CNS) regions in vivo, we examined the phenotype of cells that express EGFP in mice that are double transgenic for NG2CreBAC and the Cre reporter Z/EG. The fate of NG2 cells can be studied in these mice by permanent expression of EGFP in cells that have undergone Cre-mediated recombination in NG2 cells. We find that NG2 cells give rise to oligodendrocytes in both gray and white matter of the spinal cord and cerebellum, and to protoplasmic astrocytes in the gray matter of the spinal cord. However, NG2 cells do not give rise to astrocytes in the white matter of the spinal cord and cerebellum. These observations indicate that NG2 cells serve as precursor cells for oligodendrocytes and a subpopulation of protoplasmic astrocytes throughout the rostrocaudal axis of the CNS.</p>","PeriodicalId":19153,"journal":{"name":"Neuron glia biology","volume":"4 1","pages":"19-26"},"PeriodicalIF":0.0,"publicationDate":"2008-02-01","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"https://sci-hub-pdf.com/10.1017/S1740925X09000015","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"27836122","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":0,"RegionCategory":"","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
{"title":"Glutamate elicits release of BDNF from basal forebrain astrocytes in a process dependent on metabotropic receptors and the PLC pathway.","authors":"Ying Y Jean, Lauren D Lercher, Cheryl F Dreyfus","doi":"10.1017/S1740925X09000052","DOIUrl":"https://doi.org/10.1017/S1740925X09000052","url":null,"abstract":"<p><p>A key neurotrophin responsible for the survival and function of basal forebrain (BF) cholinergic neurons is brain-derived neurotrophic factor (BDNF). A number of studies now indicate that a source of this factor may be BF astrocytes. This study was designed to define the role of BF-astrocyte-derived BDNF on cholinergic neurons. Moreover, it investigated regulatory events that modulate BDNF content and release. In initial work BDNF derived from BF-astrocyte-conditioned medium (ACM) was found to increase both numbers of BF acetylcholinesterase (AChE+) cholinergic neurons and the cholinergic synthetic enzyme choline acetyltransferase (ChAT). Western blots, immunocytochemistry and pharmacological inhibition studies revealed that glutamate, through group I metabotropic glutamate receptors (mGluR), increases the intracellular levels of BDNF in BF astrocytes in culture, as well as its release. Furthermore, the release of BDNF is mediated by the actions of PLC, IP3 and internal stores of Ca2+. These results suggest that BF astrocytes serve as local sources of BDNF for cholinergic neurons, and that they may be regulated as such by the neuronal signal, glutamate, through the mediation of group I metabotropic receptors and the PLC pathway.</p>","PeriodicalId":19153,"journal":{"name":"Neuron glia biology","volume":"4 1","pages":"35-42"},"PeriodicalIF":0.0,"publicationDate":"2008-02-01","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"https://sci-hub-pdf.com/10.1017/S1740925X09000052","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"28106666","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":0,"RegionCategory":"","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
{"title":"Interaction between glutamate signalling and immune attack in damaging oligodendrocytes.","authors":"Carlos Matute","doi":"10.1017/S1740925X08000033","DOIUrl":"https://doi.org/10.1017/S1740925X08000033","url":null,"abstract":"<p><p>Glutamate is the principal excitatory neurotransmitter in the CNS, but it is also a potent neurotoxin that can kill nerve cells. Glutamate damages oligodendrocytes, like neurons, by excitotoxicity which is caused by sustained activation of AMPA, kainate and NMDA receptors. Glutamate excitotoxicity depends entirely on Ca(2+) overload of the cytoplasm and can be initiated by disruption of glutamate homeostasis. Thus, inhibition of glutamate uptake in isolated oligodendrocytes in vitro and in the optic nerve in vivo, is sufficient to trigger cell death which is prevented by glutamate receptor antagonists. In turn, activated, but not resting microglia, can compromise glutamate homeostasis and induce oligodendrocyte excitotoxicity, which is attenuated either by AMPA/kainate antagonists or by the blockade of the system x(c)- antiporter present in microglia. By contrast, non-lethal, brief, activation of glutamate receptors in oligodendrocytes rapidly sensitizes these cells to complement attack. Intriguingly, these effects are exclusively mediated by kainate receptors which induce Ca(2+) overload of the cytosol and the generation of reactive oxygen species. In conjunction, these observations reveal novel mechanisms by which neuroinflammation alters glutamate homeostasis and triggers oligodendrocyte death. Conversely, they also show how glutamate signaling in oligodendrocytes might induce immune attack. In both instances direct activation of glutamate receptors present in oligodendrocytes plays a pivotal role in either initiating or executing death signals, which might be relevant to the pathogenesis of white matter disorders.</p>","PeriodicalId":19153,"journal":{"name":"Neuron glia biology","volume":"3 4","pages":"281-5"},"PeriodicalIF":0.0,"publicationDate":"2007-11-01","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"https://sci-hub-pdf.com/10.1017/S1740925X08000033","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"27543403","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":0,"RegionCategory":"","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}