Proteomic analysis of optic nerve lipid rafts reveals new paranodal proteins

Targeted inactivation of the Septin2 and Septin9 genes in myelinating Schwann cells of mice

The formation of axon-enwrapping myelin sheaths by oligodendrocytes in the central nervous system involves the assembly of a scaffolding septin filament comprised of the subunits SEPTIN2, SEPTIN4, SEPTIN7 and SEPTIN8. Conversely, in the peripheral nervous system (PNS), myelin is synthesized by a different cell type termed Schwann cells, and it remained unknown if septins also assemble as a multimer in PNS myelin. According to prior proteome analysis, PNS myelin comprises the subunits SEPTIN2, SEPTIN7, SEPTIN8, SEPTIN9, and SEPTIN11, which localize to the paranodal and abaxonal myelin subcompartments. Here, we use the Cre/loxP-system to delete the Septin9-gene specifically in Schwann cells, causing a markedly reduced abundance of SEPTIN9 in sciatic nerves, implying that Schwann cells are the main cell type expressing SEPTIN9 in the nerve. However, Septin9-deficiency in Schwann cells did not affect the abundance or localization of other septin subunits. In contrast, when deleting the Septin2-gene in Schwann cells the abundance of all relevant septin subunits was markedly reduced, including SEPTIN9. Notably, we did not find evidence that deleting Septin2 or Septin9 in Schwann cells impairs myelin biogenesis, nerve conduction velocity or motor/sensory capabilities, at least at the assessed timepoints. Our data thus show that SEPTIN2 but not SEPTIN9 is required for the formation or stabilization of a septin multimer in PNS myelin in vivo; however, its functional relevance remains to be established.

Neuronally expressed a-series gangliosides are sufficient to prevent the lethal age-dependent phenotype in GM3-only expressing mice

Gangliosides are expressed on plasma membranes throughout the body and enriched in the nervous system. A critical role for complex a- and b-series gangliosides in central and peripheral nervous system ageing has been established through transgenic manipulation of enzymes in ganglioside biosynthesis. Disrupting GalNAc-transferase (GalNAc-T), thus eliminating all a- and b-series complex gangliosides (with consequent over-expression of GM3 and GD3) leads to an age-dependent neurodegeneration. Mice that express only GM3 ganglioside (double knockout produced by crossing GalNAc-T-/- and GD3 synthase-/- mice, Dbl KO) display markedly accelerated neurodegeneration with reduced survival. Degenerating axons and disrupted node of Ranvier architecture are key features of complex ganglioside-deficient mice. Previously, we have shown that reintroduction of both a- and b-series gangliosides into neurons on a global GalNAcT-/- background is sufficient to rescue this age-dependent neurodegenerative phenotype. To determine the relative roles of a- and b-series gangliosides in this rescue paradigm, we herein reintroduced GalNAc-T into neurons of Dbl KO mice, thereby reconstituting a-series but not b-series complex gangliosides. We assessed survival, axon degeneration, axo-glial integrity, inflammatory markers and lipid-raft formation in these Rescue mice compared to wild-type and Dbl KO mice. We found that this neuronal reconstitution of a-series complex gangliosides abrogated the adult lethal phenotype in Dbl KO mice, and partially attenuated the neurodegenerative features. This suggests that whilst neuronal expression of a-series gangliosides is critical for survival during ageing, it is not entirely sufficient to restore complete nervous system integrity in the absence of either b-series or glial a-series gangliosides.

Transient receptor potential vanilloid subtype 1 depletion mediates mechanical allodynia through cellular signal alterations in small-fiber neuropathy

Transient receptor potential vanilloid subtype 1 (TRPV1) is a polymodal nociceptor that monitors noxious thermal sensations. Few studies have addressed the role of TRPV1 in mechanical allodynia in small-fiber neuropathy (SFN) caused by sensory nerve damage. Accordingly, this article reviews the putative mechanisms of TRPV1 depletion that mediates mechanical allodynia in SFN. The intraepidermal nerve fibers (IENFs) degeneration and sensory neuronal injury are the primary characteristics of SFN. Intraepidermal nerve fibers are mainly C-polymodal nociceptors and Aδ-fibers, which mediated allodynic pain after neuronal sensitization. TRPV1 depletion by highly potent neurotoxins induces the upregulation of activating transcription factor 3 and IENFs degeneration which mimics SFN. TRPV1 is predominately expressed by the peptidergic than nonpeptidergic nociceptors, and these neurochemical discrepancies provided the basis of the distinct pathways of thermal analgesia and mechanical allodynia. The depletion of peptidergic nociceptors and their IENFs cause thermal analgesia and sensitized nonpeptidergic nociceptors respond to mechanical allodynia. These distinct pathways of noxious stimuli suggested determined by the neurochemical-dependent neurotrophin cognate receptors such as TrkA and Ret receptors. The neurogenic inflammation after TRPV1 depletion also sensitized Ret receptors which results in mechanical allodynia. The activation of spinal TRPV1(+) neurons may contribute to mechanical allodynia. Also, an imbalance in adenosinergic analgesic signaling in sensory neurons such as the downregulation of prostatic acid phosphatase and adenosine A1 receptors, which colocalized with TRPV1 as a membrane microdomain also correlated with the development of mechanical allodynia. Collectively, TRPV1 depletion-induced mechanical allodynia involves a complicated cascade of cellular signaling alterations.

Mitochondrial dynamics and bioenergetics regulated by netrin-1 in oligodendrocytes

Mitochondria are dynamic organelles that produce energy and molecular precursors that are essential for myelin synthesis. Unlike in neurons, mitochondria in oligodendrocytes increase intracellular movement in response to glutamatergic activation and are more susceptible to oxidative stress than in astrocytes or microglia. The signaling pathways that regulate these cell type-specific mitochondrial responses in oligodendrocytes are not understood. Here, we visualized mitochondria migrating through thin cytoplasmic channels crossing myelin basic protein-positive compacted membranes and localized within paranodal loop cytoplasm. We hypothesized that local extracellular enrichment of netrin-1 might regulate the recruitment and function of paranodal proteins and organelles, including mitochondria. We identified rapid recruitment of mitochondria and paranodal proteins, including neurofascin 155 (NF155) and the netrin receptor deleted in colorectal carcinoma (DCC), to sites of contact between oligodendrocytes and netrin-1-coated microbeads in vitro. We provide evidence that Src-family kinase activation and Rho-associated protein kinase (ROCK) inhibition downstream of netrin-1 induces mitochondrial elongation, hyperpolarization of the mitochondrial inner membrane, and increases glycolysis. Our findings identify a signaling mechanism in oligodendrocytes that is sufficient to locally recruit paranodal proteins and regulate the subcellular localization, morphology, and function of mitochondria.

Treatment with methyl-β-cyclodextrin prevents mechanical allodynia in resiniferatoxin neuropathy in a mouse model

Specialized microdomains which have cholesterol-rich membrane regions contain transient receptor potential vanilloid subtype 1 (TRPV1) are involved in pain development. Our previous studies have demonstrated that the depletion of prostatic acid phosphatase (PAP) – a membrane-bound ectonucleotidase ­– and disordered adenosine signaling reduce the antinociceptive effect. The role of membrane integrity in the PAP-mediated antinociceptive effect in small-fiber neuropathy remains unclear, especially with respect to whether TRPV1 and PAP are colocalized in the same microdomain which is responsible for PAP-mediated antinociception. Immunohistochemistry was conducted on the dorsal root ganglion to identify the membrane compositions, and pharmacological interventions were conducted using methyl-β-cyclodextrin (MβC) – a membrane integrity disruptor that works by depleting cholesterol – in pure small-fiber neuropathy with resiniferatoxin (RTX). Immunohistochemical evidence indicated that TRPV1 and PAP were highly colocalized with flotillin 1 (66.7%±9.7%) and flotillin 2 (73.7%±6.0%), which reside in part in the microdomain. MβC mildly depleted PAP, which maintained the ability to hydrolyze phosphatidylinositol 4,5-bisphosphate [PI(4,5)P2] and delayed the development of mechanical allodynia. MβC treatment had no role in thermal transduction and neuronal injury following RTX neuropathy. In summary, this study demonstrated the following: (1) membrane cholesterol depletion preserves PAP-mediated antinociception through PI(4,5)P2 hydrolysis and (2) pain hypersensitivity that develops after TRPV1(+) neuron depletion-mediated neurodegeneration following RTX neuropathy is attributable to the downregulation of PAP analgesic signaling.

Summary: The role and mechanism of cholesterol-rich membrane integrity in pain development for small-fiber neuropathy remains unclear. Depletion of membrane cholesterol contents preserves functional PAP profiles and the antinociceptive effect after RTX neuropathy.

The proteome of normal human retrobulbar optic nerve and sclera

The optic nerve is a white matter tract that conveys visual information to the brain. The sclera comprises the white, protective outer layer of the eye. A characterization of the proteome of normal human retrobulbar optic nerve and sclera may facilitate studies of the eye. We conducted a proteomic analysis of optic nerve and sclera from five adults. Proteins were fractionated using SDS-PAGE. After in-gel digestion, peptides were analyzed using LC-MS/MS on an Orbitrap Elite mass spectrometer. We identified 2711 non-redundant proteins in retrobulbar optic nerve and 1945 non-redundant proteins in sclera. Optic nerve proteins included proteins expressed by oligodendrocytes (laminin, proteolipid protein, fibronectin), myelin proteins (myelin basic protein, myelin-associated glycoprotein), and paranodal structural proteins (ankyrin β, spectrin). Sclera included 18 collagen protein chains, small leucine-rich proteoglycans (decorin, biglycan, lumican, keratocan, prolargin, fibromodulin, mimecan), non-collagenous glycoproteins (fibronectin, vitronectin, laminin), extracellular matrix proteins (thrombospondins 1-4, dystroglycan, transgelins 1-3), and integrins alpha-V, alpha-1 and 2, beta-1, -2, and -5. Twenty-one unambiguous alternative splicing protein isoforms were identified in optic nerve and ten unambiguous alternative splicing protein isoforms were identified in sclera. The mass spectrometry proteomics data have been deposited to the ProteomeXchange Consortium via the PRIDE partner repository with the dataset identifier PXD001581.

Myelination of the nervous system: mechanisms and functions

Myelination of axons in the nervous system of vertebrates enables fast, saltatory impulse propagation, one of the best-understood concepts in neurophysiology. However, it took a long while to recognize the mechanistic complexity both of myelination by oligodendrocytes and Schwann cells and of their cellular interactions. In this review, we highlight recent advances in our understanding of myelin biogenesis, its lifelong plasticity, and the reciprocal interactions of myelinating glia with the axons they ensheath. In the central nervous system, myelination is also stimulated by axonal activity and astrocytes, whereas myelin clearance involves microglia/macrophages. Once myelinated, the long-term integrity of axons depends on glial supply of metabolites and neurotrophic factors. The relevance of this axoglial symbiosis is illustrated in normal brain aging and human myelin diseases, which can be studied in corresponding mouse models. Thus, myelinating cells serve a key role in preserving the connectivity and functions of a healthy nervous system.

The node of Ranvier in CNS pathology

Healthy nodes of Ranvier are crucial for action potential propagation along myelinated axons, both in the central and in the peripheral nervous system. Surprisingly, the node of Ranvier has often been neglected when describing CNS disorders, with most pathologies classified simply as being due to neuronal defects in the grey matter or due to oligodendrocyte damage in the white matter. However, recent studies have highlighted changes that occur in pathological conditions at the node of Ranvier, and at the associated paranodal and juxtaparanodal regions where neurons and myelinating glial cells interact. Lengthening of the node of Ranvier, failure of the electrically resistive seal between the myelin and the axon at the paranode, and retraction of myelin to expose voltage-gated K⁺ channels in the juxtaparanode, may contribute to altering the function of myelinated axons in a wide range of diseases, including stroke, spinal cord injury and multiple sclerosis. Here, we review the principles by which the node of Ranvier operates and its molecular structure, and thus explain how defects at the node and paranode contribute to neurological disorders.

Septins in the glial cells of the nervous system

The capacity of cytoskeletal septins to mediate diverse cellular processes is related to their ability to assemble as distinct heterooligomers and higher order structures. However, in many cell types the functional relevance of septins is not well understood. This minireview provides a brief overview of our current knowledge about septins in the non-neuronal cells of the vertebrate nervous system, collectively termed ‘glial cells’, i.e., astrocytes, microglia, oligodendrocytes, and Schwann cells. The dysregulation of septins observed in various models of myelin pathology is discussed with respect to implications for hereditary neuralgic amyotrophy (HNA) caused by mutations of the human SEPT9-gene.

Neuro-glial interactions at the nodes of Ranvier: implication in health and diseases

Specific cell adhesion molecules (CAMs) are dedicated to the formation of axo-glial contacts at the nodes of Ranvier of myelinated axons. They play a central role in the organization and maintenance of the axonal domains: the node, paranode, and juxtaparanode. In particular, CAMs are essential for the accumulation of voltage-gated sodium channels at the nodal gap that ensures the rapid and saltatory propagation of the action potentials (APs). The mechanisms regulating node formation are distinct in the central and peripheral nervous systems, and recent studies have highlighted the relative contribution of paranodal junctions and nodal extracellular matrix. In addition, CAMs at the juxtaparanodal domains mediate the clustering of voltage-gated potassium channels which regulate the axonal excitability. In several human pathologies, the axo-glial contacts are altered leading to disruption of the nodes of Ranvier or mis-localization of the ion channels along the axons. Node alterations and the failure of APs to propagate correctly from nodes to nodes along the axons both contribute to the disabilities in demyelinating diseases. This article reviews the mechanisms regulating the association of the axo-glial complexes and the role of CAMs in inherited and acquired neurological diseases.

Nfasc155H and MAG are specifically susceptible to detergent extraction in the absence of the myelin sphingolipid sulfatide

Mice incapable of synthesizing the myelin lipid sulfatide form paranodes that deteriorate with age. Similar instability also occurs in mice that lack contactin, contactin-associated protein or neurofascin155 (Nfasc155), the proteins that cluster in the paranode and form the junctional complex that mediates myelin-axon adhesion. In contrast to these proteins, sulfatide has not been shown to be enriched in the paranode nor has a sulfatide paranodal binding partner been identified; thus, it remains unclear how the absence of sulfatide results in compromised paranode integrity. Using an in situ extraction procedure, it has been reported that the absence of the myelin sphingolipids, galactocerebroside and sulfatide, increased the susceptibility of Nfasc155 to detergent extraction. Here, employing a similar approach, we demonstrate that in the presence of galactocerebroside but in the absence of sulfatide Nfasc155 is susceptible to detergent extraction. Furthermore, we use this in situ approach to show that stable association of myelin-associated glycoprotein (MAG) with the myelin membrane is sulfatide dependent while the membrane associations of myelin/oligodendrocyte glycoprotein, myelin basic protein and cyclic nucleotide phosphodiesterase are sulfatide independent. These findings indicate that myelin proteins maintain their membrane associations by different mechanisms. Moreover, the myelin proteins that cluster in the paranode and require sulfatide mediate myelin-axon adhesion. Additionally, the apparent dependency on sulfatide for maintaining Nfasc155 and MAG associations is intriguing since the fatty acid composition of sulfatide is altered and paranodal ultrastructure is compromised in multiple sclerosis. Thus, our findings present a potential link between sulfatide perturbation and myelin deterioration in multiple sclerosis.

Complex I inhibition in the visual pathway induces disorganization of the node of Ranvier

Mitochondrial defects can have significant consequences on many aspects of neuronal physiology. In particular, deficiencies in the first enzyme complex of the mitochondrial respiratory chain (complex I) are considered to be involved in a number of human neurodegenerative diseases. The current work highlights a tight correlation between the inhibition of complex I and the state of axonal myelination of the optic nerve. Exposing the visual pathway of rats to rotenone, a complex I inhibitor, resulted in disorganization of the node of Ranvier. The structure and function of the node depend on specific cell adhesion molecules, among others, CASPR (contactin associated protein) and contactin. CASPR and contactin are both on the axonal surfaces and need to be associated to be able to anchor their myelin counterpart. Here we show that inhibition of mitochondrial complex I by rotenone in rats induces reactive oxygen species, disrupts the interaction of CASPR and contactin couple, and thus damages the organization and function of the node of Ranvier. Demyelination of the optic nerve occurs as a consequence which is accompanied by a loss of vision. The physiological impairment could be reversed by introducing an alternative NADH dehydrogenase to the mitochondria of the visual system. The restoration of the nodal structure was specifically correlated with visual recovery in the treated animal.

Excitable domains of myelinated nerves: axon initial segments and nodes of Ranvier

Neurons are highly polarized cells. They can be subdivided into at least two structurally and functionally distinct domains: somatodendritic and axonal domains. The somatodendritic domain receives and integrates upstream input signals, and the axonal domain generates and relays outputs in the form of action potentials to the downstream target. Demand for quick response to the harsh surroundings prompted evolution to equip vertebrates' neurons with a remarkable glia-derived structure called myelin. Not only Insulating the axon, myelinating glia also rearrange the axonal components and elaborate functional subdomains along the axon. Proper functioning of all theses domains and subdomains is vital for a normal, efficient nervous system.

Polarization and myelination in myelinating glia

Myelinating glia, oligodendrocytes in central nervous system and Schwann cells in peripheral nervous system, form myelin sheath, a multilayered membrane system around axons enabling salutatory nerve impulse conduction and maintaining axonal integrity. Myelin sheath is a polarized structure localized in the axonal side and therefore is supposed to be formed based on the preceding polarization of myelinating glia. Thus, myelination process is closely associated with polarization of myelinating glia. However, cell polarization has been less extensively studied in myelinating glia than other cell types such as epithelial cells. The ultimate goal of this paper is to provide insights for the field of myelination research by applying the information obtained in polarity study in other cell types, especially epithelial cells, to cell polarization of myelinating glia. Thus, in this paper, the main aspects of cell polarization study in general are summarized. Then, they will be compared with polarization in oligodendrocytes. Finally, the achievements obtained in polarization study for epithelial cells, oligodendrocytes, and other types of cells will be translated into polarization/myelination process by Schwann cells. Then, based on this model, the perspectives in the study of Schwann cell polarization/myelination will be discussed.

Axons and myelinating glia: An intimate contact

The coordination of the vertebrate nervous system requires high velocity signal transmission between different brain areas. High speed nerve conduction is achieved in the myelinated fibers of both the central and the peripheral nervous system where the myelin sheath acts as an insulator of the axon. The interactions between the glial cell and the adjacent axon, namely axo-glial interactions, segregate the fiber in distinct molecular and functional domains that ensure the rapid propagation of action potentials. These domains are the node of Ranvier, the paranode, the juxtaparanode and the internode and are characterized by multiprotein complexes between voltage-gated ion channels, cell adhesion molecules, members of the Neurexin family and cytoskeletal proteins. In the present review, we outline recent evidence on the key players of axo-glial interactions, depicting their importance in myelinated fiber physiology and disease.

Drosophila adducin regulates Dlg phosphorylation and targeting of Dlg to the synapse and epithelial membrane

Adducin is a cytoskeletal protein having regulatory roles that involve actin filaments, functions that are inhibited by phosphorylation of adducin by protein kinase C. Adducin is hyperphosphorylated in nervous system tissue in patients with the neurodegenerative disease amyotrophic lateral sclerosis, and mice lacking β-adducin have impaired synaptic plasticity and learning. We have found that Drosophila adducin, encoded by hu-li tai shao (hts), is localized to the post-synaptic larval neuromuscular junction (NMJ) in a complex with the scaffolding protein Discs large (Dlg), a regulator of synaptic plasticity during growth of the NMJ. hts mutant NMJs are underdeveloped, whereas over-expression of Hts promotes Dlg phosphorylation, delocalizes Dlg away from the NMJ, and causes NMJ overgrowth. Dlg is a component of septate junctions at the lateral membrane of epithelial cells, and we show that Hts regulates Dlg localization in the amnioserosa, an embryonic epithelium, and that embryos doubly mutant for hts and dlg exhibit defects in epithelial morphogenesis. The phosphorylation of Dlg by the kinases PAR-1 and CaMKII has been shown to disrupt Dlg targeting to the NMJ and we present evidence that Hts regulates Dlg targeting to the NMJ in muscle and the lateral membrane of epithelial cells by controlling the protein levels of PAR-1 and CaMKII, and consequently the extent of Dlg phosphorylation.

Building Excitable Membranes

Multiple plasma membrane proteins such as ion transporters and ion channels are involved in electrogenesis by setting resting membrane potentials and triggering/propagating action potentials. Recent findings strongly suggest that some of these membrane proteins are selectively transported into membrane microdomains termed lipid rafts. There appear to be multiple mechanisms for the specific protein translocation to lipid rafts, and many of these proteins exhibit distinct properties when inserted into the raft microdomains. Here the authors review the plasma membrane ion channels specifically localized at membrane lipid rafts in neurons. The mechanisms to selectively translocate these molecules to the lipid rafts and the consequences of the trafficking are also discussed.

A draft of the human septin interactome

Background

Septins belong to the GTPase superclass of proteins and have been functionally implicated in cytokinesis and the maintenance of cellular morphology. They are found in all eukaryotes, except in plants. In mammals, 14 septins have been described that can be divided into four groups. It has been shown that mammalian septins can engage in homo- and heterooligomeric assemblies, in the form of filaments, which have as a basic unit a hetero-trimeric core. In addition, it has been speculated that the septin filaments may serve as scaffolds for the recruitment of additional proteins.

Methodology/Principal Findings

Here, we performed yeast two-hybrid screens with human septins 1–10, which include representatives of all four septin groups. Among the interactors detected, we found predominantly other septins, confirming the tendency of septins to engage in the formation of homo- and heteropolymeric filaments.

Conclusions/Significance

If we take as reference the reported arrangement of the septins 2, 6 and 7 within the heterofilament, (7-6-2-2-6-7), we note that the majority of the observed interactions respect the “group rule”, i.e. members of the same group (e.g. 6, 8, 10 and 11) can replace each other in the specific position along the heterofilament. Septins of the SEPT6 group preferentially interacted with septins of the SEPT2 group (p<0.001), SEPT3 group (p<0.001) and SEPT7 group (p<0.001). SEPT2 type septins preferentially interacted with septins of the SEPT6 group (p<0.001) aside from being the only septin group which interacted with members of its own group. Finally, septins of the SEPT3 group interacted preferentially with septins of the SEPT7 group (p<0.001). Furthermore, we found non-septin interactors which can be functionally attributed to a variety of different cellular activities, including: ubiquitin/sumoylation cycles, microtubular transport and motor activities, cell division and the cell cycle, cell motility, protein phosphorylation/signaling, endocytosis, and apoptosis.

The spectrin-ankyrin-4.1-adducin membrane skeleton: adapting eukaryotic cells to the demands of animal life

The cells in animals face unique demands beyond those encountered by their unicellular eukaryotic ancestors. For example, the forces engendered by the movement of animals places stresses on membranes of a different nature than those confronting free-living cells. The integration of cells into tissues, as well as the integration of tissue function into whole animal physiology, requires specialisation of membrane domains and the formation of signalling complexes. With the evolution of mammals, the specialisation of cell types has been taken to an extreme with the advent of the non-nucleated mammalian red blood cell. These and other adaptations to animal life seem to require four proteins--spectrin, ankyrin, 4.1 and adducin--which emerged during eumetazoan evolution. Spectrin, an actin cross-linking protein, was probably the earliest of these, with ankyrin, adducin and 4.1 only appearing as tissues evolved. The interaction of spectrin with ankyrin is probably a prerequisite for the formation of tissues; only with the advent of vertebrates did 4.1 acquires the ability to bind spectrin and actin. The latter activity seems to allow the spectrin complex to regulate the cell surface accumulation of a wide variety of proteins. Functionally, the spectrin-ankyrin-4.1-adducin complex is implicated in the formation of apical and basolateral domains, in aspects of membrane trafficking, in assembly of certain signalling and cell adhesion complexes and in providing stability to otherwise mechanically fragile cell membranes. Defects in this complex are manifest in a variety of hereditary diseases, including deafness, cardiac arrhythmia, spinocerebellar ataxia, as well as hereditary haemolytic anaemias. Some of these proteins also function as tumor suppressors. The spectrin-ankyrin-4.1-adducin complex represents a remarkable system that underpins animal life; it has been adapted to many different functions at different times during animal evolution.

Myelin sheaths are formed with proteins that originated in vertebrate lineages

All vertebrate nervous systems, except those of agnathans, make extensive use of the myelinated fiber, a structure formed by coordinated interplay between neuronal axons and glial cells. Myelinated fibers, by enhancing the speed and efficiency of nerve cell communication allowed gnathostomes to evolve extensively, forming a broad range of diverse lifestyles in most habitable environments. The axon-covering myelin sheaths are structurally and biochemically novel as they contain high portions of lipid and a few prominent low molecular weight proteins often considered unique to myelin. Here we searched genome and EST databases to identify orthologs and paralogs of the following myelin-related proteins: (1) myelin basic protein (MBP), (2) myelin protein zero (MPZ, formerly P0), (3) proteolipid protein (PLP1, formerly PLP), (4) peripheral myelin protein-2 (PMP2, formerly P2), (5) peripheral myelin protein-22 (PMP22) and (6) stathmin-1 (STMN1). Although widely distributed in gnathostome/vertebrate genomes, neither MBP nor MPZ are present in any of nine invertebrate genomes examined. PLP1, which replaced MPZ in tetrapod CNS myelin sheaths, includes a novel 'tetrapod-specific' exon (see also Möbius et al., 2009). Like PLP1, PMP2 first appears in tetrapods and like PLP1 its origins can be traced to invertebrate paralogs. PMP22, with origins in agnathans, and STMN1 with origins in protostomes, existed well before the evolution of gnathostomes. The coordinated appearance of MBP and MPZ with myelin sheaths and of PLP1 with tetrapod CNS myelin suggests interdependence - new proteins giving rise to novel vertebrate structures.