Membrane topology of the myelin/oligodendrocyte glycoprotein

Myelin/oligodendrocyte glycoprotein (MOG), a specific component of the mammalian central nervous system, is located on the surface of the oligodendrocyte plasma membrane and the outermost lamellae of mature myelin; it is expressed during the latter steps of myelinogenesis. It has been shown that MOG may play a pathological role in autoimmune demyelinating diseases of the central nervous system, although its physiological function remains unknown. MOG is an integral membrane glycoprotein with an extracellular immunoglobulin-like domain and two hydrophobic segments which were predicted to be membrane-spanning on the basis of hydropathy analysis. As a first step in elucidation of MOG function, we have investigated its membrane topology, combining immunofluorescence studies on cultured oligodendrocytes and MOG-transfected Chinese hamster ovary cells with biochemical analyses, including in vitro translation, membrane insertion and protease-digestion assays. Our results indicate that the C-terminal tail of MOG is located into the cytoplasm, and that only the first hydrophobic region of MOG spans the membrane whereas the second hydrophobic region appears to be semi-embedded in the lipid bilayer, lying partially buried in the membrane with its N-terminal and C-terminal boundaries facing the cytoplasm.

Endogenous retroviruses and multiple sclerosis. II. HERV-7q

The search for new endogenous retroviral sequences, on the basis of sequence homologies with the pol gene of the recently reported multiple sclerosis associated retrovirus (MSRV), allowed us to identify a full length endogenous retrovirus sequence located on the long arm of human chromosome 7. This retrovirus, HERV-7q, includes in its env region, within a single 1,620 bp open reading frame, a 664 bp domain almost identical to a 3' non-coding region of the rab7 gene. Transcripts encompassing both the env and the 3' LTR regions of HERV-7q have already been identified as expressed sequence tags, suggesting that this env-like gene might code for a 538 amino acid long deduced protein.

Immunoelectron microscopic localization of the M6a antigen in rat brain

The monoclonal antibody M6-7, which recognizes both native and denatured immunopurified M6a antigen, was used in the present immunocytochemical study to localize its corresponding antigen in young rat brain. Strong labelling was observed in the cerebellar molecular layer, which corresponds to heavily stained axon terminals originating from granule cells. The immunodeposit, as observed by electron microscopy, is present only on the cytoplasmic side of the presynaptic membrane and on the membrane of synaptic vesicles. In contrast, the Purkinje cells and their processes are unstained. Stained synapses are also found, although less frequently, in several other cerebral areas. The pattern of staining at these synapses is similar to that observed in the cerebellar molecular layer. It is hypothesized, on the basis of its restricted distribution in certain neuronal endings and its high homology with myelin proteolipids, that the M6a antigen revealed by the M6-7 antibody is probably involved in a specific biological function in these structures.

[Endogenous retroviral sequences analogous to that of the new retrovirus MSRV associated with multiple sclerosis (part 1)]

Multiple sclerosis (MS) is still of unknown origin and may involve autoimmune, genetic and viral components in a pathogenic sequence whose relative importance is yet to be determined. A peptide, isolated from the cerebrospinal fluid of MS patients, is similar to a fragment of the pol protein reverse transcriptase (RT) of the newly reported MSRV retrovirus. The 700 amino acid sequence of MSRV-RT is closely related to a novel human retroviral-like sequences. We also identified a gag-like sequence upstream of this human genomic RT-like sequence, which allowed us to identify altogether 4,000 nucleotides, possibly coding for an endogenous retroviruses. Homologous sequences found in other locations in the human genome seem to characterize a new family of retroviral endogenous sequences, which may be of relevance to multiple sclerosis.

[Cloning of testican/SPOCK in man and mouse. Neuromuscular expression perspectives in pathology]

We have recently cloned a novel proteoglycan initially identified in human testis and hence previously called testican. A close examination of the overall protein structure reveals three main regions: four osteonectin/SPARC-like domains encompassing the amino-terminal and central part of the deduced protein, a Kazal-like motif overlapping the third domain, and the CWCV domain in the carboxyl-terminal end region of the protein core. We propose to call it SPOCK, the acronym of SPARC/Osteonectin CWCV and Kazal-like domains proteoglycan, according to its specific multidomain structure. To get further insight into the function, a Northern blot analysis was performed in order to determine the site of expression in various adult tissues; a 5.2 kb transcript appeared only but strongly in mouse brain. The structure of the murine brain proteoglycan was determined through molecular cloning; human and mouse deduced proteins are highly homologous with 95% overall amino acid identity. Murine brain serial sections hybridized with cDNA and immunological probes revealed identical distribution in discrete cerebral regions, such as CA3 hippocampal region and cerebellum. Immunoelectron microscopy showed the antigen selectively localized in the post-synaptic density of scattered pyramidal neurons and Purkinje cells. Structural analysis, a main expression in nervous system and preliminary assignment of the human gene in a critical region for neuropathologies, suggest that SPOCK may be of importance in neural development and neurodegenerative diseases.

Structure and cellular distribution of mouse brain testican. Association with the postsynaptic area of hippocampus pyramidal cells

The complete deduced primary structure of mouse brain testican has been established from cDNA cloning. The cDNA encodes a polypeptide of 442 amino acids belonging to the proteoglycan family. The mouse brain testican core protein is 95% identical to its human testicular counterpart. In situ hybridization investigations revealed that mouse testican mRNA is mainly present in a subpopulation of pyramidal neurons localized in the CA3 area of the hippocampus. An immunocytochemical approach, with antibodies directed against an overexpressed chimeric antigen, produced in bacterial systems, showed that testican is associated with the postsynaptic region of these pyramidal neurons. Testican includes several putative functional domains related to extracellular or pericellular proteins associated with binding and/or regulatory functions. On the basis of its structural organization and its occurrence in postsynaptic areas, this proteoglycan might contribute to various neuronal mechanisms in the central nervous system.

Developmental expression of the C1G5F2 antigen in cultured rat oligodendroglial cells

The C1G5F2 antigen is a newly described minor myelin antigen of the central nervous system. Its expression compared with that of some other main myelin protein components (Wolfgram W1 protein, myelin basic proteins (MBP) and proteolipids) was investigated in rat oligodendrocytes derived from 10-day-old primary glial cell cultures and subcultured for several days in a chemically defined medium. It was demonstrated immunocytochemically that this antigen is detected later than the major myelin markers. All cells immunoreactive with the monoclonal antibody C1G5F2 were always labeled either by W1-, MBP- or proteolipid-specific antisera. It was also shown at the electron microscopic level that this antigen is mainly expressed on the surface of the extremities of the fine oligodendroglial processes. All these observations suggest that the C1G5F2 antigen may be a useful marker for a specific step in the oligodendrocyte maturation stage.

Comparative immunohistochemical study of C1G5F2 antigen and myelin/oligodendrocyte glycoprotein (MOG) expression in brain of several animal species

The localisation of the myelin/oligodendrocyte specific antigen C1G5F2 and the myelin/oligodendrocyte glycoprotein (MOG) was studied in parallel in the brain of various species throughout the phylogenetic line of vertebrates. This immunofluorescence study was performed on unfixed brain sections by using the newly described monoclonal antibody C1G5F2 and polyclonal anti-MOG antibody. The antigen C1G5F2 is detected from the reptilian class onwards whereas MOG is only found in mammals. Both antibodies clearly stained only the myelin sheaths in the brain of adult animals. The phylogenetic distribution of the C1G5F2 antigen compared to the other well known myelin proteins may indicate that it has a specific function during myelination. Moreover, evidence is given that the C1G5F2 antigen is a new minor myelin protein distinct from the glycoprotein MOG.

Characterization and expression of the cDNA coding for the human myelin/oligodendrocyte glycoprotein

We report here the characterization of a full-length cDNA encoding the human myelin/oligodendrocyte glycoprotein (MOG). The sequence of the coding region of the human MOG cDNA is highly homologous to that of other previously cloned mouse, rat, and bovine MOG cDNAs, but the 3' untranslated region differs by an insertion of an Alu sequence between nucleotides 1,590 and 1,924. Accordingly, northern blot analyzes with cDNA probes corresponding to the coding region or the 3' untranslated Alu-containing sequence revealed a single band of 2 kb, rather than the 1.6 kb of bovine, rat, or mouse MOG cDNA(s). Immunocytochemical analysis of HeLa cells transfected with human MOG cDNA, which was performed using a specific antibody raised against whole MOG, clearly indicated that MOG is expressed at the cell surface as an intrinsic protein. These data are in accordance with the predicted amino acid sequence, which contains a signal peptide and two putative transmembrane domains. The knowledge of the human MOG sequence should facilitate further investigations on its potential as a target antigen in autoimmune demyelinating diseases like multiple sclerosis.

A new oligodendrocyte specific plasma membrane surface protein identified by a monoclonal antibody produced in vitro

This paper describes a novel monoclonal antibody (C1G5F2) derived from mice splenocytes immunized in vitro with a wheat germ agglutinin glycoprotein fraction isolated from bovine central nervous system (CNS) myelin. Immunohistochemical reactions with C1G5F2 were investigated on rat brain sections during the active period of myelination. From day 10 to 13 postnatally, no stained structures were observed throughout the whole brain. The first immunolabeled myelin fibers were detected within the pons at day 14, and the white matter areas in the cerebrum started to be stained some days later. White matter areas of the cerebellum were clearly immunopositive after the third week. There was a strong positive signal on myelin fibers in the cerebrum at day 30. By contrast, no immunolabeled cell bodies of oligodendrocytes were observed throughout the brain. The other neural cell types were also not labeled. This C1G5F2 monoclonal antibody bound mainly to the extracytosolic membrane surface of the processes of live cultured oligodendrocytes derived from newborn rat brain but was unreactive with live or fixed astrocytes and neurons maintained in culture. No immunostaining was detected in the peripheral nervous system or in the spleen, liver, or pancreas. The C1G5F2 epitope containing antigen may therefore be considered as a CNS myelin/oligodendrocyte specific molecule. Sodium deoxycholate-Tween 20 extracts of secondary oligodendrocyte cultures, biotinylated with biotin hydrazide, were used to attempt the purification of the antigen with C1G5F2 IgMs linked to antimouse IgM agarose. A main broad biotinylated protein band of 54-58 kDa molecular mass was noted. In a second approach, the antigen was immunopurified from cultured oligodendrocytes as an immune complex using biotinylated C1G5F2 IgMs. A distinct protein doublet of 53-56 kDa was also observed. It is postulated that this antigen may play an essential role in myelin formation and could be a possible target in diseases restricted to CNS myelin.

Myelin/oligodendrocyte glycoprotein is a member of a subset of the immunoglobulin superfamily encoded within the major histocompatibility complex

Myelin/oligodendrocyte glycoprotein (MOG) is found on the surface of myelinating oligodendrocytes and external lamellae of myelin sheaths in the central nervous system, and it is a target antigen in experimental autoimmune encephalomyelitis and multiple sclerosis. We have isolated bovine, mouse, and rat MOG cDNA clones and shown that the developmental pattern of MOG expression in the rat central nervous system coincides with the late stages of myelination. The amino-terminal, extracellular domain of MOG has characteristics of an immunoglobulin variable domain and is 46% and 41% identical with the amino terminus of bovine butyrophilin (expressed in the lactating mammary gland) and B-G antigens of the chicken major histocompatibility complex (MHC), respectively; these proteins thus form a subset of the immunoglobulin superfamily. The homology between MOG and B-G extends beyond their structure and genetic mapping to their ability to induce strong antibody responses and has implications for the role of MOG in pathological, autoimmune conditions. We colocalized the MOG and BT genes to the human MHC on chromosome 6p21.3-p22. The mouse MOG gene was mapped to the homologous band C of chromosome 17, within the M region of the mouse MHC.

Biochemical and immunohistochemical studies with specific polyclonal antibodies directed against bovine myelin/oligodendrocyte glycoprotein

Bovine myelin/oligodendrocyte glycoprotein (MOG) was purified from a Wolfgram protein fraction of brain myelin by molecular sieving and preparative gel electrophoresis. The N-terminal sequence of this wheat germ agglutinin reacting glycoprotein was determined. Antibodies against purified MOG and synthetic N-terminal octapeptide of MOG were produced in rabbits. Respective affinity purified antibody preparations gave identical results on Western blots. Treatment with specific glycosidases indicated that the oligosaccharide chains of MOG are only of N-chain type. This glycoprotein seems to be restricted to mammalian species since it was not detected in other animal species, ranging from fish up to reptiles. Immunohistochemical investigations on rat brain sections revealed that MOG is restricted to myelin sheaths and oligodendrocytes, thus corroborating previous results obtained with the MOG 8-18C5 monoclonal antibody. Decreased staining pattern in Jimpy brain further attested its specific localization in myelin-related structures. The octapeptide site-specific antibodies were not reactive on brain sections which may be attributed to the burying of this N-terminal sequence in the membrane. These MOG polyclonal antibodies appear to be valuable tools for further studies concerning this minor glycoprotein.

Proteolipid DM-20 predominates over PLP in peripheral nervous system

The major central nervous system (CNS) myelin proteolipid (PLP) is also expressed in the peripheral nervous system (PNS). This paper gives evidence that DM-20, an isoform of PLP, also occurs in rat sciatic nerves, where, in contrast to what is seen in CNS myelin, it predominates over PLP. This conclusion was reached on the basis of results obtained by immunoblot analysis of a crude proteolipid extract from adult peripheral nerve with two site-specific anti-proteolipid (PLP and DM-20) antibodies. This finding was further corroborated by characterization of the products obtained by Polymerase Chain Reaction (PCR) amplification of cDNAs synthesized from total RNA of 14-day-old sciatic nerves. The significance of the occurrence of these proteolipids in PNS remains obscure.

In situ localization of NF-H neurofilament subunit mRNAs in rat brain

The expression of NF-H neurofilament subunit mRNAs was investigated in the rat brain at different ontogenic stages. The levels of NF-H mRNAs vary 15-fold among brain regions with the highest level in the brainstem. In situ localization studies revealed that the NF-H mRNAs are mainly concentrated in the brainstem motoneuron nuclei. By increasing the sensitivity of the hybridization method, NF-H mRNAs could also be localized in neurons present in the cortex, thalamus and hippocampus areas. Minor amounts of NF-H mRNAs were already detected at 17-day embryonic stages.

Immunohistochemical studies on cross-transplantations between jimpy, shiverer, and normal newborn mice

Cross-transplantations of neural tissue have been performed between jimpy (jp), shiverer (shi), and normal mice. Taking advantage of the absence of immunodetectable myelin basic protein (MBP) in the shi brain, jp myelin has been identified in the shi recipient by using an anti-MBP antiserum. By contrast, shi as well as normal myelin have been identified in the jp brain by using an anti-C-terminal hexapeptide of the proteolipid protein (PLP) (this PLP hexapeptide being absent in the jp PLP). When transplanted under homochronic conditions (newborn into newborn), jp oligodendrocytes (ODC) express their usual phenotype in a normal or a shi environment, suggesting that at birth the jp ODCs phenotype is strictly established and cannot be modified by environmental conditions. The reverse transplantations (newborn shi or normal into newborn jp brain) demonstrate that the jp environment does not modify the phenotype of normal or shi ODCs. Finally, these experiments demonstrated a normal timing of differentiation of jp axons and of jp ODCs.

Oligodendrocyte cell surface recognized by a novel monoclonal antibody specific to sulfatide

A rat monoclonal antibody (OL-1) was obtained by in-vitro immunization of rat spleenocytes with paraformaldehyde-fixed primary cultured glial cells derived from newborn rat brain and subsequent fusion with a rat myeloma cell line. The antibody secreted by the hybridoma immunostains live rat and mouse oligodendrocytes in primary and secondary cultures. The antibody binds specifically to oligodendrocytes and myelin structures in-situ. Radioimmunolabelling assays with a number of purified glycolipids offer thin layer chromatography separation show that OL-1 antibody binds strongly to sulfatide and to a lesser extent to galactosyl diglyceride.

The large neurofilament subunit (NF-H) of the rat: cDNA cloning and in situ detection

A lambda gt11 expression library was screened with a polyclonal antiserum directed against Wla Wolfgram protein which corresponds to the 2',3'-cyclic nucleotide 3'-phosphohydrolase. This antiserum also recognizes epitopes of the high protein subunit of neurofilaments (NF-H). An NF-H cDNA clone (pNF-H1: 1.7 kb) was isolated and characterized. Using pNF-H1 as a probe, a second cDNA clone (pNF-H2: 3 kb) was isolated from the lambda gt11 library. The two clones were sequenced and pNF-H2 was found to encode 80% of rat NF-H protein (coil-2 and C-terminal region). The C-terminal region contains an unusual sequence with stretches of repeats of Lys-Ser-Pro which represent possible phosphorylation sites. Specific localization in neurons of the corresponding mRNA was demonstrated by in situ hybridization using the pNF-H1 as a probe.

A chemically defined medium for the culture of mature oligodendrocytes

A new chemically defined medium consisting of equal parts of Dulbecco modified Eagle's and Ham's F-12 media supplemented with insulin, sodium selenite, putrescine, and D+ galactose, which allows the long-term survival of mature oligodendrocyte pure cultures, is described. Immunohistochemical staining has shown that over 90% of the cells become positive for myelin proteins shortly following subculture. Contaminating astrocytes (2%) do not survive in this medium. Biochemical data have indicated that these purified oligodendrocytes express 2'3'-cyclic nucleotide 3'-phosphohydrolase and UDP-galactose ceramide galactosyltransferase activities. Electron microscopical examination revealed that the oligodendrocytes were mostly of medium-dark type and appeared to be identical to cells cultured in serum-containing medium. The ability to maintain pure oligodendrocyte cultures in such a defined medium will allow investigations concerning exogenous and endogenous factors involved in oligodendrocyte metabolism.

Immunological investigation of a 21-kilodalton cytosolic basic protein in rat brain

A gamma-globulin fraction was isolated from the antiserum raised against a 21-kilodalton (kDa) basic protein which was purified from bovine brain cytosol. This fraction was employed to study the immunocytochemical localization of the 21-kDa protein during the development of rat brain. Immunostaining was observed on oligodendrocytes and their processes at all stages of development investigated. This immunostaining was less prominent in very young and adult brains. Myelin fibers were always moderately stained; neurons and astrocytes were not immunolabelled. The electron microscopic study revealed that the labelling covers the entire cytoplasm of the oligodendrocytes, being more dense along the membranes of the rough endoplasmic reticulum and the plasma membrane. Other cytoplasmic organelles were unstained. The present report emphasizes that 21-kDa protein may serve as a specific marker for oligodendroglial cells in the central nervous system despite its presence in peripheral organs.

UDPgalactose:ceramide galactosyltransferase in cultured oligodendrocytes: an enzymological and immunological study

The developmental expression of UDPgalactose:ceramide galactosyltransferase (CGalT), an enzyme marker of one myelinogenic activity in nervous tissue, was studied in cultured oligodendrocytes. The activity of CGalT in cultures followed a characteristic pattern of developmental changes. In the primary cultures these changes could be represented by a biphasic curve with a maximum of enzymatic activity at about the 25th day in culture. After purifying the oligodendrocytes from the primary cultures and replating them in culture dishes, similar developmental changes of CGalT were observed. In the subcultures prepared from 20-day-old primary cultures the activity of CGalT per oligodendrocyte increased from 1.3 x 10(-6) nmol/hr on day 4 to 3.7 x -6 nmol/hr on day 21. Immunocytochemical studies with the antiserum against rat brain CGalT showed the presence of CGalT+ oligodendrocytes after 7 days in the primary culture (earliest time studied), later on the number of CGalT+ oligodendrocytes increased until 28 days (latest time examined). In the subcultures of purified oligodendrocytes the bulk of oligodendrocytes was stained by the anti-CGalT antibodies after 15 days. These results suggest that the initial expression of CGalT in oligodendroglial cultures involves an increase of the number of CGalT+ oligodendrocytes and of the amount of enzyme protein per cell.

A morphological and biochemical study of the myelin-like membrane structures formed in cultures of pure oligodendrocytes

This study reports the production of myelin-like membranes in oligodendrocyte subcultures derived from 20-day-old primary glial cell cultures of newborn rat brain. These multi-layered structures show a variable number of membrane turns; up to 10 concentric lamellae are found in 3- to 4-week-old subcultures. When they are compacted, alternate dense and intraperiodic lines with a periodicity of 11.2 nm are noticeable. The most typical myelin proteins were detected straight on the multi-lammellar structures by a gold immunocytochemical method. Subcellular fractions containing these myelin-like structures were isolated by ultracentrifugation on a discontinuous sucrose gradient. They were analysed by sodium dodecylsulfate-polyacrylamide gel electrophoresis and immunoblotting; UDP-galactose: ceramide galactosyltransferase and 2',3'-cyclic nucleotide 3'-phosphohydrolase activities were also measured. The results indicate that the multi-layered membrane profiles have many characteristics of the myelin found in vivo; nevertheless some differences were still apparent. Our data support the concept of the cultured oligodendrocytes expressing the intrinsic myelinogenic properties and possessing a basic developmental program of myelination, apparently in the absence of stimuli coming from other brain cells.

Arrest of proteolipid transport through the Golgi apparatus in Jimpy brain

Immunocytochemical investigations were performed on Jimpy and control mouse brains using three specific anti-myelin proteolipids antisera: immunoaffinity purified multivalent anti-(PLP + DM-20) proteolipid antibodies, anti-C-terminal hexapeptide 271-276 and anti-tridecapeptide 117-129 antisera. The results show that oligodendrocytes and myelin sheaths in normal mouse brain are labelled to the same extent by the three specific antisera; in contrast, in Jimpy brain these cellular structures are only stained by the multivalent antibodies and the site-specific, anti-tridecapeptide antiserum. The absence of labelling with C-terminal hexapeptide antiserum in mutant brain is interpreted as the result of either a large deletion or a point mutation producing a frameshift in the C-terminal part of the sequences of the proteolipids PLP and DM-20. Furthermore, we show that this mutation prevents the normal transport of proteolipid molecules through the Golgi apparatus. The existence of a minor, extra-Golgi apparatus metabolic route for proteolipids to myelin structures is also discussed.

Immunocytochemical localization of UDP-galactose: ceramide galactosyltransferase in myelin and oligodendroglial cells of rat brain

Specific antibodies were prepared against rat-brain UDP-galactose:ceramide galactosyltransferase (CGalT) and used to study the localization of this enzyme at light and electron microscopic levels. Using an immunocytochemical technique the presence of CGalT was revealed in the cytoplasm and processes of oligodendrocytes and in myelin sheaths of developing and adult rat brain. No immunostaining was detected in neurons or astrocytes. At the ultrastructural level the immunostaining of oligodendrocytes was most intense at the periphery of cytoplasm and probably included plasma membrane. Among the intracellular organelles of oligodendrocytes, specific labelling was occasionally seen in the stacks of Golgi apparatus membranes. In myelin sheaths anti-CGalT staining seems to be restricted to the outermost and innermost lamellae. The finding of CGalT in distant portions of oligodendrocyte processes and in loosely wrapped myelin membranes might indicate that myelin galactocerebrosides are synthesized in the proximity of the site of their incorporation into the newly formed myelin.

Identification of two cell surface proteins of rat brain oligodendrocytes in culture

Antibodies specific for the surface of oligodendrocytes were prepared by incubating living cultures of pure oligodendrocytes with a crude anti-oligodendrocyte antiserum. These specific antibodies, when used in the technique of immunoelectroblotting, led to the characterization of at least two major plasma membrane proteins of 43 kilodaltons (kDa) and 53 kDa, respectively, as accessible at the external surface of the oligodendrocytes. The 53-kDa protein was also found in oligodendrocyte-conditioned medium in significant amounts. Additional oligodendrocyte surface proteins were also detected in the Wolfgram protein fraction.

UDPgalactose:ceramide galactosyltransferase of rat brain: a new method of purification and production of specific antibodies

A new method for purification of UDPgalactose:ceramide galactosyltransferase (EC 2.4.1.45) is described. The principal steps involved solvent extraction at -70 degrees C, Triton X-100 extraction, and DEAE-Sephadex and Blue Sepharose chromatography. The active configuration of the enzyme was stabilized by phospholipids and a rapid loss of enzymatic activity was observed after removal of these lipids. The inactive enzyme could be fully reactivated in the presence of brain phospholipids dispersed in a Triton X-100-containing buffer. The purified enzyme preparation showed two major components by polyacrylamide gel electrophoresis in the presence of sodium dodecyl sulfate with apparent molecular weights of 50-70,000. The 53,000-dalton protein was isolated by preparative gel electrophoresis in the presence of sodium dodecyl sulfate and used to produce antibodies against UDPgalactose:ceramide galactosyltransferase.

A specific immunological probe for the major myelin proteolipid. Confirmation of a deletion in DM-20

Major myelin proteolipid (MMPL, also called PLP) and DM-20 are the two major intrinsic membrane proteins of CNS myelin. A specific immunological probe was obtained for MMPL by raising antibodies against the synthetic tridecapeptide 117-129 of MMPL. Antibodies against this peptide reacted with the MMPL but did not cross react with DM-20, while both proteolipids had been shown previously to be recognized by antibodies directed against the C-terminal hexapeptide of MMPL. This is in accordance with previous findings showing that DM-20 differs only from MMPL by a deletion of residues 100-140 (+/- few units). Furthermore, this site-specific immunological probe also recognizes MMPL in its native form in oligodendrocytes in primary glial cell cultures.

Molecular cloning and nucleotide sequence of a cDNA clone coding for rat brain myelin proteolipid

A cDNA library from rat brain was constructed in pBR322 and screened with a 14-mer mixed oligonucleotide probe based on residues 231-235 of bovine proteolipid (PLP). A positive clone was isolated: it contained a 1334-base-pair cDNA insert and was subjected to DNA sequence analysis. The cDNA encoded information for the 276 amino acids of rat PLP. Comparison with bovine PLP sequence showed a complete amino acid sequence homology except for 4 amino acid residues.

Site-specific antibodies to rat myelin proteolipids directed against the C-terminal hexapeptide

A site-specific antiserum against the rat myelin proteolipids was produced in rabbits by injection of a synthetic polypeptide composed of the C-terminal amino acids of the proteolipid sequence. The immunogenic hexapeptide H-Gly-Arg-Gly-Thr-Lys-Phe-OH was coupled to chicken egg-albumin with dimethylsuberimidate. Antibodies specific for this peptide reacted with the 2 myelin proteolipid protein bands after SDS polyacrylamide gel electrophoresis and electrophoretic transfer onto nitrocellulose. Immunocytochemical investigations with this anti-peptide antiserum showed that the Golgi complexes of the oligodendrocytes were highly labeled as noted previously with multivalent antibodies. Labeling of vesicles and discontinuous staining of the plasmalemma were also observed in the most actively myelinating oligodendrocytes. In contrast to previous results, the major dense line was free of staining; this may indicate that at this site the C-terminal hexapeptide is inaccessible to these antibodies and perhaps buried in the lipid bilayer, in disagreement with the proposed organization of the myelin proteolipid in the myelin membrane.

Precursor cells of oligodendrocytes in rat primary cultures

In monolayer primary cultures of brain from newborn rats, which contain astrocytes and oligodendrocytes, a new morphological cell type (flat black cells) was observed. Microphotographs of different areas of the monolayer, taken every 30 min, showed that these flat black cells can divide and that they undergo morphological transformation in vitro. They give rise to oligodendrocytes which were identified by their characteristics morphology but also by their content of W1 Wolfgram protein. These findings suggest that the flat black cells are precursors for oligodendrocytes, in culture.

Immunohistochemical study with an anti-myelin serum. A marker for all glial cells except 'dark' oligodendrocytes

The usefulness of an anti-myelin antiserum as a possible marker for glial cells and related structures was investigated using rat brain. As expected, the myelin fibers were heavily stained but the neuronal cells and their processes were unreactive. The oligodendrocytes, identified on electron microscopy, revealed labelling of only the light and medium types, but not the dark cells. These results indicate that the suggested morphological classification of oligodendrocytes may be based on varying amounts of myelin antigen synthesis. Astrocytes from all areas, Golgi epithelial cells, Bergmann fibers and some subependymal cells also reacted with this anti-myelin antiserum but the staining was abolished completely by preabsorption with kidney powder. In contrast, the myelin fibers and the light and medium oligodendrocytes could still be labelled. We conclude that this anti-myelin antiserum should prove useful in studies of oligodendrocytes in the central nervous system.

Immunocytochemical demonstration of the transport of myelin proteolipids through the Golgi apparatus

Purified antibodies directed against myelin proteolipids were isolated by affinity chromatography of whole serum obtained from rabbits inoculated with myelin. These antibodies were specific for light, medium and dark oligodendrocytes. Astrocytes, neurons and their processes were not reactive. Immunocytochemical investigations showed that the membranes of the Golgi complex are highly labeled by these antibodies. Diffuse cytoplasmic labeling was only observed on the light and medium oligodendrocytes and was absent from the dark types. Vesicles possessing a punctate staining were detected in the vicinity of the Golgi complex and the oligodendroglial membrane. A discontinuous labeling of the plasmalemma appears to be characteristic of the actively myelinating light and medium oligodendrocytes. In compact myelin sheaths positive immunostaining was only detected at the dense line. The immunocytochemical localization of the myelin proteolipids in the oligodendrocytes is in accordance with previously published biochemical data.

Detection of Wolfgram W1 protein, myelin basic proteins and proteolipids in cultured oligodendrocytes by the electro-immunoblotting method

Oligodendrocytes, mechanically obtained from primary cultures of newborn rat brain, were investigated by a sensitive electro-immunoblotting method for the presence of the characteristic myelin proteins: Wolfgram W1 protein, basic proteins and proteolipids. These three major myelin protein types were detectable from the 20th to the 40th day in culture. The present biochemical findings are in accordance with previous immunohistochemical data and provide additional evidence that oligodendrocytes in culture are capable of synthesizing every myelin and oligodendrocyte marker found in vivo, in the absence of neurones.

Brain proteolipids. Isolation, purification and effect on ionic permeability of membranes

Proteolipid apoproteins have been isolated from a whole bovine brain homogenate by chloroform/methanol extraction, and fractionated by chromatography on modified (lipophilic) Sephadex, followed by ion-exchange chromatography on CM-Trisacryl. The various final, highly hydrophobic, fractions are homogeneous (sodium dodecyl sulfate/polyacrylamide gel electrophoresis). Transmembrane ion transfers were studied by 22Na + flux and electrical conductance measurements. Single channel events were observed at low protein concentrations, in particular with one of the final homogeneous apoproteolipids of molecular mass 24 kDa.

An immunohistochemical study of two myelin-specific proteins in enriched oligodendroglial cell cultures combined with an autoradiographic investigation using [3H]thymidine

The aim of the present work was to examine the possible relationship between proliferation and expression of 2 myelin specific proteins in cultured oligodendroglial cells. Mixed cultures of glial cells, from newborn rat brain, containing astroglia and oligodendroglia were grown in 2 different culture media, minimum Eagle's medium and Waymouth's medium both supplemented with 10% calf serum in presence or absence of adult rat brain soluble extract. The proliferative activity of the cells was followed over a 28-day period by autoradiography after radioactive thymidine incorporation. It was found that in cultures grown in Waymouth's medium the proportion of oligodendroglial cells was higher and that proliferation was more active than in minimum Eagle's medium. Addition of brain extract elicited a stimulation of the proliferation of the cells in the 2 basal media. Under all conditions W1 protein appeared earlier than MBP by immunofluorescent visualization. Some oligodendroglial cells synthesizing W1 protein were still able to proliferate. MBP appears to be a marker of a later stage of cell maturation since very few MBP-positive cells incorporated tritiated thymidine. More cells contained MBP in the presence of brain extract. These results suggest that oligodendroglial cell maturation proceeds by steps, the step of W1 protein expression is compatible with proliferation while that of MBP expression appears at the end of the proliferation phase.

Surface labelling of oligodendrocytes with anti-myelin serum in cell cultures from the rat brain. Light- and electron-microscopic immunocytochemical studies

Antiserum produced in rabbits against purified myelin contains antibodies that bind to the surface of cells having multiple branched processes in live cultures of cerebral hemispheres of newborn rats. The identity of these cells was determined by double immunolabelling experiments with other specific antigenic markers (W1 Wolfgram protein, myelin basic proteins, glial fibrillary acidic protein). It was demonstrated that the cells are a subclass of oligodendrocytes which have reached a certain degree of maturation; nearly all of them contain basic proteins. Indeed, a number of oligodendrocytes, that contain the W1 protein, and may or may not have processes, are not surface-labelled in similar conditions. The usefulness of such an anti-myelin serum in the isolation of pure oligodendrocytes is discussed.

Comparative localization of Wolfgram W1 and myelin basic proteins in the rat brain during ontogenesis

Antisera raised in rabbits against myelin basic proteins (MBP) and Wolfgram W1 protein isolated from rat myelin were used to study the maturation of oligodendrocytes in the developing rat nervous system. Both proteins were localized immunohistochemically at the light and electron microscopical levels in rat brain from the time of their first appearance to the adult stage. Oligodendrocytes were first detected by their positive staining with W1 antiserum two days after birth and at 1-3 days later with MBP antiserum. At 8-10 days, the number of oligodendrocytes labelled with both sera increases and the myelinated fibre pathways were clearly visible. Labelling with W1 antiserum was observed in oligodendrocytes at all stages from 2 days after birth to adulthood and in myelin fibers when they were present. In contrast, staining of oligodendroglial cells with MBP declined during the period of rapid myelination (20-25 days after birth) and finally disappeared, whereas myelin staining was still apparent. The electron microscopical study revealed that the synthesis of Wolfgram proteins occurred mostly at the peripheral cytoplasmic ribosomes of the cells, from where they were probably transported to processes engaged in myelination. The electron micrographs also showed that the sites of MBP synthesis seemed to be more uniformly distributed over the entire cytoplasm.

Demonstration of a specific localization of carbonic anhydrase C in the glial cells of rat CNS by an immunohistochemical method

The localization of carbonic anhydrase C isoenzyme in the central nervous system (CNS) of the rat has been investigated using the indirect immunoperoxidase technique, at both optic and electron microscopic levels. Evidence is presented for a specific localization of the enzyme in the cytoplasm of the oligodendrocytes and astrocytes. Myelinated fibers show a weak staining. The positive reaction is restricted to the cytoplasmic areas of the myelin sheath and does not appear in the compact myelin. Neuronal cell bodies do not stain at all. A strong positive reaction to the antiserum was also observed in the choroid plexus.

Ultrastructural localization study of two Wolfgram proteins in rat brain tissue

The ultrastructural immunohistochemical localization of Wolfgram proteins W1 and W2 is described in young rat brain tissue. The labelling by the antiserum to W1 is restricted to oligodendroglial cells and myelin sheaths. The plasma membrane of the cells as well as the polysomes are positively stained whereas the mitochondria and the nuclei are always free of labelling. Glial cell processes with definite organelles, which are involved in the myelination of neighbouring axons, are also positive to the antiserum. In the myelin sheaths, the positive staining occurs predominantly at the dense period line of the innermost and outermost lamellae. The present results add further evidence for a specific local synthesis of these Wolfgram proteins in oligodendroglial cells during myelination.

Immunohistochemical studies of Wolfgram proteins in central nervous system of neurological mutant mice

Immunohistochemical localization of Wolfgram proteins has been studied by the indirect immunoperoxidase technique with Wolfgram protein W1 antibodies in the nervous system of myelin deficient mutant mice: Jimpy, MSD and Quaking. In all these mutants, the myelinated fibers and the oligodendroglial cells (few in number) in the corpus callosum and the white matter of the cerebellum folium show a positive reaction to protein W1. These observations are in accordance with the immunological studies showing that the two major Wolfgram proteins, W1 and W2, of mutant mice have immunological similarities with that of the controls.