Synthesis of Sulfatide by Cultured Rat Schwann Cells

Abstract: The ³⁵S sulfolipids synthesized by purified cultures of rat Schwann cells, fibroblasts, and a rat cell line (RN2) were studied. Schwann cell ³⁵S sulfolipids were almost entirely [³⁵S]sulfatide, as shown by TLC in two different solvent systems with unlabeled authentic sulfatide run in the same track. RN2 and fibroblasts did not synthesize significant amounts of sulfatide, by the same criteria. Previous studies failed to detect any characteristic myelin components, including sulfatide, on Schwann cells after several days in culture (Brockes et al., 1980a; Mirsky et at., 1980). My results show that Schwann cells continue to synthesize some sulfatide in the absence of neurons.     

The Role and Metabolism of Sulfatide in the Nervous System

3-O-sulfogalactosylceramide or sulfatide is a major component of the myelin sheath in the central and peripheral nervous system. The examination of mice deficient in the sulfatide-synthesizing enzyme, cerebroside sulfotransferase, provided new insight into the role of sulfatide in the differentiation of myelinating cells, formation of the paranodal junction, and myelin maintenance. Although in general regarded as a marker for oligodendrocytes and Schwann cells, sulfatide is also present in astrocytes and neurons. The relatively low amount of sulfatide in neurons can dramatically increase in the absence of the sulfatide-degrading enzyme, arylsulfatase A, as in metachromatic leukodystrophy. Recent advance in the understanding of this disease comes from studies on new transgenic mouse models. Significant changes in sulfatide levels have also been observed more recently in Alzheimer's disease and other diseases, suggesting that sulfatide might be involved in the pathogenesis of these diseases as well. This review summarizes recent studies on the physiological and pathophysiological role of sulfatide using transgenic mice deficient in its synthesis or degradation.     

Regulation of Myelin P0 Glycoprotein Synthesis in Cultured Rat Schwann Cells and Continuous Rat PNS Cell Lines

We studied the effects of agents that raise intracellular cyclic AMP on synthesis of myelin components by cultured neonatal rat sciatic nerve Schwann cells and by continuous PNS cell lines derived from the fusion of neonatal rat sciatic nerve Schwann cells with rat RN22 Schwannoma. Treatment with N6,2'-O-dibutyryl cyclic AMP (dibutyryl cyclic AMP) caused a fourfold increase in Schwann cell incorporation of 35SO4 into sulfogalactosylceramide (sulfatide), and elicited a 10- to 20-fold increase in such incorporation by the continuous PNS cell lines; a similar effect on PNS cell line sulfatide radiolabelling was obtained with forskolin. Cultured Schwann cells expressed barely detectable levels of myelin P0 glycoprotein (P0) mRNA and myelin basic protein (MBP) mRNA. Treatment of the Schwann cells with axolemmal fragments or with dibutyryl cyclic AMP did not elicit a detectable increase in the levels of these mRNAs. The PNS cell lines constitutively expressed much higher levels of P0 mRNA than did the Schwann cells, and synthesized immunochemically demonstrable P0 glycoprotein, but did not express MBP. Treatment of the PNS cell lines with dibutyryl cyclic AMP markedly reduced expression of P0 mRNA and also diminished immunoreactive P0 glycoprotein. These PNS cell lines should prove useful for further studies of the control of Schwann cell differentiation.     

Emergence of three myelin proteins in oligodendrocytes cultured without neurons

Oligodendrocytes, the myelin-forming cells of the central nervous system, were cultured from newborn rat brain and optic nerve to allow us to analyze whether two transmembranous myelin proteins, myelin-associated glycoprotein (MAG) and proteolipid protein (PLP), were expressed together with myelin basic protein (MBP) in defined medium with low serum and in the absence of neurons. Using double label immunofluorescence, we investigated when and where these three myelin proteins appeared in cells expressing galactocerebroside (GC), a specific marker for the oligodendrocyte membrane. We found that a proportion of oligodendrocytes derived from brain and optic nerve invariably express MBP, MAG, and PLP about a week after the emergence of GC, which occurs around birth. In brain-derived oligodendrocytes, MBP and MAG first emerge between the fifth and the seventh day after birth, followed by PLP 1 to 2 d later. All three proteins were confined to the cell body at that time, although an extensive network of GC positive processes had already developed. Each protein shows a specific cytoplasmic localization: diffuse for MBP, mostly perinuclear for MAG, and particulate for PLP. Interestingly, MAG, which may be involved in glial-axon interactions, is the first myelin protein detected in the processes at approximately 10 d after birth. MBP and PLP are only seen in these locations after 15 d. All GC-positive cells express the three myelin proteins by day 19. Simultaneously, numerous membrane and myelin whorls accumulate along the oligodendrocyte surface. The sequential emergence, cytoplasmic location, and peak of expression of these three myelin proteins in vitro follow a pattern similar to that described in vivo and, therefore, are independent of continuous neuronal influences. Such cultures provide a convenient system to study factors regulating expression of myelin proteins.     

A Monoclonal Antibody Raised to Corpus Callosum Extract Reacts with 2'',3''-Cyclic Nucleotide 3''-Phosphohydrolase

Monoclonal antibody against 2',3'-cyclic nucleotide 3'-phosphohydrolase (CNP) was generated by fusing mouse myeloma cells with spleen cells from BALB/c mice immunized with delipidated white matter from rat corpus callosum. The antibody was characterized by solid-phase radioimmunoassay, immunoblot of sodium dodecyl sulfate-polyacrylamide gel electrophoresis (SDS-PAGE), immunoprecipitation from C6 glioma cells, and indirect immunofluorescence staining of monolayer cultures containing oligodendrocytes. The monoclonal antibody bound specifically to an intracellular antigen of oligodendrocytes, but not to Schwann cells, astrocytes, neurons, or fibroblast cytoplasm. The immunoblot of SDS-PAGE of CNS myelin showed that the antibody identified two protein bands at 48,000 and 50,000 molecular weight. These proteins were not identified in peripheral nervous system myelin. The monoclonal antibody immunoprecipitated CNP enzyme activity from extracts of C6 glioma cells. This monoclonal antibody should prove useful in further study of this myelin-specific enzyme in CNS myelin and in cells responsible for myelin production.     

Immunocytochemical and RT-PCR analysis of connexin36 in cultures of mammalian glial cells

The expression of connexin36 (Cx36) was studied in primary cultures of rat brain glial cells: mature astrocytes, ameboid and ramified microglia and immature oligodendrocytes (at middle period of myelinogenesis). The data from these cells were compared with those obtained from cultures of neocortical and hypothalamic neurons. mRNA encoding Cx36 was investigated by RT-PCR, the Cx36 protein by immunocytochemistry using a polyclonal antibody against Cx36 in cells characterized by antibodies specific for the single cell types. The Cx36 was found in oligodendrocytes, both ameboid and ramified microglial cells and in neurons. Astrocytes showed no detectable expression of the Cx36. The expression of Cx36 in oligodendrocytes and microglial cells suggests an involvement of the direct cell-cell communication channels formed by Cx36 in myelin formation and in brain development, damage and repair processes.     

Galactocerebroside is expressed by non-myelin-forming Schwann cells in situ

Interest in the glycosphingolipid galactocerebroside (GC) is based on the consensus that in the nervous system it is expressed only by myelin-forming Schwann cells and oligodendrocytes, and that it has a specific role in the elaboration of myelin sheaths. We have investigated GC distribution in two rat nerves--the sciatic, containing a mixture of myelinated and non-myelinated axons, and the cervical sympathetic trunk, in which greater than 99% of axons are non-myelinated. Immunohistochemical experiments using mono- and polyclonal GC antibodies were carried out on teased nerves and cultured Schwann cells, and GC synthesis was assayed biochemically. Unexpectedly, we found that mature non-myelin-forming Schwann cells in situ and in short-term cultures express unambiguous GC immunoreactivity, comparable in intensity to that of myelinated fibers or myelin-forming cells in short-term cultures. GC synthesis was also detected in both sympathetic trunks and sciatic nerves. In the developing sympathetic trunk, GC was first seen at day 19 in utero, the number of GC-positive cells rising to approximately 95% at postnatal day 10. In contrast, the time course of GC appearance in the sciatic nerve shows two separate phases of increase, between day 18 in utero and postnatal day 1, and between postnatal days 20 and 35, at which stage approximately 94% of the cells express GC. These time courses suggest that Schwann cells, irrespective of subsequent differentiation pathway, start expressing GC at about the same time as cell division stops. We suggest that GC is a ubiquitous component of mature Schwann cell membranes in situ. Therefore, the role of GC needs to be reevaluated, since its function is clearly not restricted to events involved in myelination.     

Cultured oligodendrocytes mimic in vivo phenotypic characteristics: Cell shape, expression of myelin-specific antigens, and membrane production

Primary cultures of neonatal mouse cerebra were maintained for up to 4 weeks in the absence of neurons. Oligodendrocytes in these cultures pass through a sequence of cytoarchitectural change and antigen expression which mimics the differentiation of oligodendrocytes in vivo. The cell bodies and processes of oligodendrocytes first express the myelin-specific antigen galactocerebroside (GC) by 2 days in vitro. Myelin basic protein (MBP) appears several days later. The majority of oligodendrocytes then proceed to elaborate large sheets of membranous material from the tips and lengths of cell processes. These membranous sheets, which contain GC and MBP, are reminiscent of unwrapped myelin profiles in vivo. As with the cell bodies and processes, GC is inserted into the sheets several days before MBP. Our results establish that oligodendrocytes cultured without neurons are able to produce extensive membranes containing myelin-specific antigens. They also suggest that oligodendrocyte shape and membrane production are, in part, regulated from within the oligodendrocyte itself.     

Evidence That Secondary Rat Schwann Cells in Culture Maintain Their Differentiated Phenotype

Schwann cells, on receiving the correct signal, will encircle an axon and wrap it with a myelin sheath. To begin examining some of the mechanisms underlying the process of myelination in vitro, we isolated Schwann cells from the sciatic nerves of neonatal rats and generated large cell populations with cholera toxin. The immunological and biochemical properties of these secondary Schwann cells were characterized after five to seven passages in the absence of axonal contact. These cells continued to express antigens found in both myelinating (P0 and 2',3'-cyclic nucleotide phosphohydrolase) and nonmyelinating cells in vivo (A5E3 and glial fibrillary acidic protein) in addition to the markers common to both types of cells (Ran-1, 217c, S-100, and laminin). Biochemical analyses showed that these cells synthesize the very-long-chain fatty acids (22-26 carbon atoms) found in myelin membranes. Moreover, the enzymes required for the synthesis of myelin glycolipids (including sphingosine acyltransferase, UDP-galactose:ceramide galactosyltransferase, and cerebroside sulfotransferase) were still active, and metabolic labeling studies showed that galactocerebroside and sulfatide were synthesized even though the galactocerebroside pool was insufficient to be detected by immunostaining. Secondary Schwann cells also synthesized four species of myelin basic protein and the major structural glycoprotein in myelin, P0. The pathway necessary for glycosylation of P0 protein remained active, and an analysis of the oligosaccharide chain revealed that approximately 70% was processed to a complex form. In summary, we found that secondary Schwann cells still express most of the immunological markers of differentiated cells and continue to synthesize low levels of myelin components. Therefore, Schwann cells do not dedifferentiate in culture, as previously believed.     

Immunoreactive myelin basic proteins are not detected when shiverer mutant Schwann cells and fibroblasts are co-cultured with normal neurons

Shiverer (shi) is an autosomal recessive mutation in mice that results in hypomyelination in the central nervous system (CNS) but normal myelination in the peripheral nervous system (PNS). Myelin basic proteins (MBPs) are virtually absent in both PNS and CNS. It is not known whether the cellular target in the PNS is the myelin-forming Schwann cell or another cell type which secondarily affects the Schwann cell. To determine the cellular target of the shi gene, we have adapted tissue culture techniques that allow co-culture of pure populations of mouse sensory neurons of one genotype with Schwann cells and fibroblasts of another genotype under conditions that permit myelin formation. These cultures were stained immunocytochemically as whole mounts to determine whether MBPs were expressed under various in vitro conditions. In single-genotype cultures, presence or absence of MBPs was consistent with earlier in vivo results: +/+ cultures were MBP-positive and shi/shi cultures were MBP-negative. In mixed-genotype cultures, visualization of MBPs in myelin accorded with the genotype of the non-neuronal Schwann cells and fibroblasts and not with the neurons--those cultures that contained +/+ non-neuronal cells were MBP-positive and those with shi/shi non-neuronal cells were MBP-negative, independent of the neuronal genotype. These results rule out neurons or circulating substances as mediators of the influence of the shi genetic locus on MBP synthesis and deposition in peripheral myelin.     

Expressing antisense P0 RNA in Schwann cells perturbs myelination.

Primary Schwann cells were infected in vitro with a recombinant retrovirus expressing a dominant selectable marker, neomycin phosphotransferase (conferring resistance to the drug G418), and antisense P0 RNA under the control of the human beta-actin promoter. A proportion of the G418-resistant cells failed to form myelin when cocultured with dorsal root ganglion neurons under conditions that promote Schwann cell differentiation. These cells expressed high levels of P0 antisense RNA. Among the impaired cells, the majority had segregated and ensheathed individual axon but had not differentiated further. They did not express P0 but did express myelin- associated glycoprotein and galactocerebroside. A minority of partially inhibited Schwann cells were also observed that elaborated thin myelin sheaths containing variable numbers of compacted and noncompacted lamellae. These data indicate that restricting the level of P0 expression inhibits spiralling of the Schwann cell membrane and subsequent compaction.     

04 and A007-sulfatide antibodies bind to embryonic Schwann cells prior to the appearance of galactocerebroside; regulation of the antigen by axon-Schwann cell signals and cyclic AMP

In the rat sciatic nerve, the relationship between Schwann cells, axons, the extracellular matrix and perineurial sheath cells undergoes extensive modification between embryo day 15 and the onset of myelination during the first postnatal day. Little is known about molecular changes in Schwann cells in this important prenatal period. In the present paper, we use immunofluorescence to study the prenatal development and postnatal regulation of the antigen(s) recognized by the 04 monoclonal antibody and a well-characterized rat monoclonal antibody to sulfatide, A007. We show that, in a series of immunochemical tests, the 04 antibody recognizes only sulfatide in neonatal and adult rat nerves. Both antibodies first bind to Schwann cells in the sciatic nerve at embryo day 16-17, and all Schwann cells bind both antibodies at birth. In the adult nerve, both nonmyelin-forming and myelin-forming cells are labelled with the antibodies. Schwann cells dissociated from embryo day 15 nerves and cultured in the absence of axons develop neither 04 nor A007 binding on schedule, and 04-positive and A007-positive Schwann cells from postnatal nerves lose the ability to bind these antibodies during the first few days in culture. Schwann cells in the distal stump of transected nerves also sharply down-regulate cell surface binding of 04. High numbers of 04-positive or A007-positive Schwann cells reappear in cultures treated with agents that mimic or elevate intracellular cAMP. We conclude that two anti-sulfatide antibodies 04 and A007, recognize an antigen, probably sulfatide, that appears very early in Schwann cell development (one to two days prior to galactocerebroside) but is nevertheless subject to upregulation by axonal contact or elevation of intracellular cAMP.     

Effects of ethanol on rat schwann cell proliferation and myelination in culture

Summary It is possible to treat dissociated embryonic rat dorsal root ganglia in culture to inhibit proliferation of all nonneuronal cells except Schwann cells. Neurons have been shown to produce a mitogenic stimulus for Schwann cells under these conditions. Additionally, myelin-competent neurons induce Schwann cells to elaborate myelin sheaths. Groups of sibling cultures were exposed to various nonlethal concentrations of ethanol (0, 43, 86, or 172 mM) for 4 wk. Culture were assessed weekly by light microscopy in a blind fashion for evidence of Schwann cell proliferation and myelin formation. Ethanol adversely affected both Schwann cell proliferation and myelin formation in culture. No obvious differences in neuronal morphology were observed among the various groups of cultures by light or electron microscopy. These observations suggest that ethanol might interfere with Schwann cell proliferation and myelin formation in culture by one or both of the following means: a) inhibit neuronal production of signals for Schwann cell proliferation and myelination or b) impede Schwann cell responses to neuronal signals. Investigation of these possibilities in culture may provide insight into neuropathologic mechanisms operative in the fetal alcohol syndrome or alcohol-associated peripheral neuropathy in humans. This work was supported by the Department of Veterans Affairs, Washington, D.C.     

Identification of New Oligodendrocyte- and Myelin-Specific Genes by a Differential Screening Approach

Abstract: We have isolated several new genes that are specifically expressed by oligodendrocytes in the CNS. This was achieved by differential screening of a rat spinal cord cDNA library with probes derived from normal and from oligodendrocyte-free spinal cord mRNAs. Four of these genes are exclusively expressed by oligodendrocytes: Three of these are not related to known genes, whereas one encodes the myelin oligodendrocyte glycoprotein (MOG). Four other genes are expressed by oligodendrocytes as well as by Schwann cells. One gene codes for apolipoprotein D, which is thought to be involved in lipid metabolism. A second cDNA sequence codes for the recently identified galactosylceramide-synthesizing enzyme UDP-galactose:ceramide galactosyl-transferase. The third gene encodes a small protein with four putative transmembrane domains that is related to a T-lymphocyte-specific membrane protein, MAL. The fourth gene encodes the rat homologue of the stearyl-CoA-desaturase 2 (SCD2) gene, which is specifically expressed in the nervous system and involved in the synthesis and regulation of long-chain unsaturated fatty acids essential for myelination. Finally, we found that a member of the β-tubulin family is highly expressed in oligodendrocytes as well as neurons. The identification of several new proteins that may play a role in myelin synthesis and sheath formation will lead to new insight into this complex mechanism.     

Enzyme levels in cultured astrocytes,oligodendrocytes and Schwann cells,and neurons from the cerebral cortex and superior cervical ganglia of the rat

Data are presented for 16 enzymes from 8 metabolic systems in cell cultures consisting of approximately 95% astrocytes and 5% oligodendrocytes. Nine of these enzymes were also measured in cultures of oligodendrocytes, Schwann cells, and neurons prepared from both cerebral cortex and superior cervical ganglia. Activities, in mature astrocyte cultures, expressed as percentage of their activity in brain, ranged from 9% for glycerol-3-phosphate dehydrogenase to over 300% for glucose-6-phosphate dehydrogenase. Creatine phosphokinase activity in astrocytes was about the same as in brain, half as high in oligodendrocytes, but 7% or less of the brain level in Schwann cells and superior cervical ganglion neurons and only 16% of brain in cortical neurons. Three enzymes which generate NADPH, the dehydrogenases for glucose-6-phosphate and 6-phosphogluconate, and the NADP-requiring isocitrate dehydrogenase, were present in astrocytes at levels at least twice that of brain. Oligodendrocytes had enzyme levels only 30% to 70% of those of astrocytes. Schwann cells had much higher lactate dehydrogenase and 6-phosphogluconate dehydrogenase activities than oligodendrocytes, but showed a remarkable similarity in enzyme pattern to those of cortical and superior cervical ganglion neurons.Special issue dedicated to Dr. Lewis Sokoloff.     

An Autoradiographic Study of Nucleic Acid and Protein Turnover in the Mammalian Neuraxis

The turnover of nucleic acids and proteins in the central nervous system has been explored by autoradiography following the subarachnoid injection of tagged precursors. Nuclear PNA of neurons and oligodendrocytes becomes radioactive earlier than cytoplasmic PNA after injection of adenine-C¹⁴ and orotic-C¹⁴ acid. By 24 hours following injection, cytoplasmic PNA is radioactive. Radioactivity persists with little decrease for as long as 51 days after an injection of adenine-C¹⁴. The cells of the ependymal lining, choroidal plexus, leptomeninges, blood vessel walls, and Schwann cells also exhibit radioactivity in PNA as judged by the loss of radioactivity following ribonuclease digestion. From the 3rd day on, increasing numbers of the aforementioned cells, with the exception of nerve cells, exhibit ribonuclease-resistant nuclear radioactivity which is abolished by deoxyribonuclease. This radioactivity indicates labelling of nuclear DNA. Following the intrathecal injection of methionine-S³⁵ and glycine-2-H³, nerve cells, oligodendrocytes, cells of ependymal lining, choroidal plexus, leptomeninges, blood vessels, and Schwann cells become radioactive. Nerve cells lose most of their radioactivity within a few hours, first from the cytoplasm and later from the nucleus. Other cell types retain their radioactivity for considerable periods of time. Although astrocytes, microglia, and satellite cells of sensory ganglia do not appear to incorporate labelled precursors into nucleic acids or proteins, reacting phagocytic microglia actively take up labelled amino acids. These results are discussed with particular reference to PNA and protein turnover in nerve cells, oligodendrocytes, and Schwann cells. It is believed that these metabolic activities in neurons are concerned in part with the elaboration of axoplasmic proteins. The nucleoprotein metabolism of oligodendrocytes and Schwann cells may be related to myelin biosynthesis both in the immature and the mature nervous system.     

Cellular Location of Glutamine Synthetase and Lactate Dehydrogenase in Oligodendrocyte-Enriched Cultures from Rat Brain

Glial cells were isolated from 1-week-old rat brain and cultured in a serum-free medium supplemented with the hormones insulin, hydrocortisone, and triiodothyronine. After 1 week in culture the cell population consisted mainly of galactocerebroside-positive cells (GC+; oligodendrocytes), the remainder of the cells being positive for glial fibrillary acidic protein (GFAP+; astrocytes). Oligodendrocytes were selectively removed from the cultures by complement-mediated cytolysis. The activities of glutamine synthetase and of various marker enzymes were measured in the nonlysed cells remaining after complement treatment of the cultures and in the culture medium containing proteins of the lysed cells. We found that the cellular activity of glutamine synthetase decreased in parallel with the lysis of GC+ cells and that the activity of glutamine synthetase in the supernatant increased. The activity of glycerol-3-phosphate dehydrogenase, a marker enzyme for oligodendrocytes, was no longer detectable in complement-treated cultures and the activity of glutamine synthetase was markedly lowered, whereas the activity of lactate dehydrogenase was as high as in untreated cultures. The location of glutamine synthetase both in oligodendrocytes and in astrocytes was confirmed by double-label immunocytochemistry with antisera against glutamine synthetase, GC, and GFAP. We conclude that in this culture system glutamine synthetase is expressed in both types of glial cells and that the activity of lactate dehydrogenase is at least one order of magnitude higher in astrocytes than in oligodendrocytes.     

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.     

Cell shape and motility of oligodendrocytes cultured without neurons

Summary Oligodendrocytes, the myelin-forming cells of the central nervous system (CNS), were cultured from newborn rat brain and optic nerve to study how they differentiate in vitro in the absence of neurons. By use of galactocerebroside (GC) as a reference marker, the development of the cell phenotype was studied with video-enhanced differential interference contrast microscopy, immunofluorescence and electron microscopy. After a few days in culture, oligodendrocytes extend 5 to 10 main processes that are very rich in microtubules, but they did not stain with a monoclonal antibody reacting with all known classes of intermediate filaments. The number of processes can vary with the substrate on which the cells are grown; fewer processes form on laminin than on polylysine coated glass. Oligodendrocytes, in a fashion similar to that of neurons appear to keep their body immobile while the long processes grow. However, while neurons display motile activities mostly at the end of the cell processes called growth cones, the oligodendrocytes display motile, actin rich filopodia and lamellipodia along the entire length of all processes. The outgrowth of motile processes from oligodendrocytes sometimes occurs preferentially towards neighboring astrocytes. Oligodendrocyte processes display intense bidirectional movement of cytoplasmic organelles. Movement of surface components also occurs since GC molecules cross-linked by antibodies move from the processes towards the cell body. Thus, oligodendrocytes cultured without neurons develop on schedule a complex phenotype similar to their in vivo counterpart. In addition, their processes are capable of specific motile activities which may function in vivo to find the target axon and to transport myelin membrane components at the site of myelin assembly.Abbreviations (CNS) Central nervous system - (DIC) Differential interference contrast - (GC) Galactocerebroside - (GFA) protein Glial fibrillary acidic - (NSE) Neuron-specific enolase     

Identification of reciprocally regulated gene modules in regenerating dorsal root ganglion neurons and activated peripheral or central nervous system glia

Differential gene expression in the rat after injury of dorsal root ganglion neurons in vivo, and simulation injury of Schwann cells and oligodendrocytes in vitro was analyzed using high-density cDNA microarrays. The analyses were carried out to study the genetic basis of peripheral nerve regeneration, and to compare gene regulation in glia of the central (oligodendrocyte) and peripheral (Schwann cell) nervous systems. The genes showing significant differential regulation in the three study groups represented all aspects of cellular metabolism. However, two unexpected observations were made. Firstly, a number of identical genes were differentially regulated in activated Schwann cells, activated oligodendrocytes and regenerating DRG neurons. Specifically, a group of 113 out of 210 genes that were down-regulated in Schwann cells upon lipopolysaccharide (LPS) treatment, were identical to genes up-regulated in the injured, regenerating DRG. Furthermore, a group of 53 out of 71 genes that were down-regulated in interferon gamma (IFN-gamma)/LPS-activated oligodendrocytes, were identical to genes up-regulated in the DRG neurons. Finally, 22 genes were common to these three groups, i.e., down-regulated in activated oligodendrocytes, down-regulated in activated Schwann cells, and up-regulated in regenerating DRG neurons. Secondly, a group of 16 cell-cycle and proliferation-related genes were up-regulated in the DRG following sciatic nerve crush, despite the absence of cells undergoing mitosis in the DRG, or any significant presence of apoptosis-related gene expression. Therefore, it appears that in these three cell types, large sets of genes are reciprocally regulated upon injury and/or activation. This suggests that the activation of the injury-related gene expression program in cell derivatives of the neuroectoderm involves, in part, highly conserved genetic elements.