Isolation and characterization of a cDNA coding for a novel human 17.3K myelin basic protein (MBP) variant

Regenerative response following stab injury in the adult zebrafish telencephalon

In contrast to mammals, the brain of the adult zebrafish has a remarkable ability to regenerate. In mammals, injuries induce proliferation of astrocytes and oligodendrocyte progenitors contributing to the formation of a glial scar. We analyzed the proliferation of glial cells and microglia in response to stab injury in the adult zebrafish telencephalon: Radial glial markers were up-regulated at the ventricle and co-expressed the proliferation nuclear antigen (PCNA). Microglia and oligodendrocyte progenitors accumulated transiently at the site of lesion. However, we could not find evidence of permanent scar formation. Parenchymal proliferation was almost negligible in comparison to the increase in proliferation at the ventricular zone. This suggests that most of the cellular material for regeneration is derived from regions of constitutive neurogenesis. Remarkably, the proliferative response is almost completely restricted to the lesioned hemisphere indicating that signals inducing regeneration remain mainly confined within the lesioned half of the telencephalon.

Expression of the transcription factor Olig2 in proliferating cells in the adult zebrafish telencephalon

The telencephalon of the adult zebrafish is highly proliferative: Dividing cells are found along the entire ventricular zone and in the parenchyma. Here, we investigated the relation of proliferating cells in the telencephalic parenchyma to the oligodendrocyte lineage. We find at least three different cell types of the oligodendrocyte lineage (olig2-and sox10-positive) in the parenchyma of the telencephalon: Proliferating progenitors (PCNA-positive), including a subpopulation of slowly dividing progenitors (long term label-retaining), as well as mature oligodendrocytes (Mbp-positive) and presumptive quiescent OPCs (neither Mbp-positive nor proliferating). Furthermore, in the ventricular zone (in and ventral to the RMS), two different subpopulations of olig2-positive cell populations are present. Since these ventricular olig2-positive cells do not express the oligodendrocyte marker sox10, it is not clear whether these cells indeed belong to the oligodendrocyte lineage. Taken together, we detected at least five different classes of olig2-positive cells in the telencephalon of the adult zebrafish.

Immunohistochemical localization of citrullinated proteins in adult rat brain

By using hybridoma technology, an IgM monoclonal antibody (F95) against multiple citrullinated synthetic and natural peptides was recently developed and used to stain immunohistochemically subsets of astrocytes and myelin basic protein (MBP) from selected regions of human brain (Nicholas and Whitaker [2002] Glia 37:328-336). With this antibody, the present study provides a more detailed localization of citrullinated epitopes in the central nervous system (CNS) by examining immunohistochemical staining patterns for F95 in the normal adult rat brain. Thus, immunohistochemical labeling for citrullinated epitopes was seen in white matter areas consistent with myelin staining; however, in general, it was more prominent and uniform in the caudal CNS (spinal cord, medulla oblongata, pons, and cerebellum) than in more rostral areas. F95 staining was also seen in cells and fibers often intimately associated with blood vessels and/or ventricular surfaces. By using dual-color immunofluorescence, the vast majority of this latter staining was colocalized within a subset of astrocytes also immunoreactive for glial fibrillary acidic protein (GFAP). By using Western blot analysis of rat brain proteins, multiple GFAP- and MBP-immunoreactive proteins and peptide fragments were seen, and many of them were also reactive with the F95 antibody. Thus, the present study not only demonstrates that citrullinated epitopes in normal rat brain are most concentrated in subsets of myelin and astrocytes but also provides evidence that GFAP, like MBP, may be present as multiple citrullinated isoforms.

Down-regulation of mu-opioid receptor expression in rat oligodendrocytes during their development in vitro

In the central nervous system, opioid receptors are found in neurons and also in glial cells. To gain more information on their presence and possibly on their function, we investigated the expression of mu-opioid receptors (MOR) during oligodendroglial cell development in two culture systems. In these models, during the first days, the cells are O-2A bipotential progenitor cells (also called OPCs; oligodendrocyte precursor cells), and then they differentiate into oligodendrocytes, which mature. In the first system, oligodendroglial cells, derived from newborn rat brain hemispheres, are grown in primary culture in the presence of a confluent layer of astrocytes, and they differentiate slowly. In the second, cells are specifically detached from the mixed cultures of the first system and are grown thereafter alone in secondary culture, a condition allowing a rapid cell differentiation. Under both conditions OPCs and immature oligodendrocytes were found to express a high level of MOR mRNA, whereas mature oligodendrocytes did not express it at all. The decrease of MOR expression during oligodendrocyte maturation was progressive, suggesting that it was not a primary effect of differentiation but an indirect secondary effect. Our study also shows that basic fibroblast growth factor (bFGF), which has been claimed by some authors to induce a dedifferentiation of the mature oligodendrocytes, and retinoic acid (RA), which had not been tested before, were not able to restore MOR expression in mature oligodendrocytes. These results indicate that bFGF and RA neither reverse the maturation process nor dedifferentiate the cells. However, RA was found to inhibit almost completely the expression of the myelin basic protein. The main result of this study is that MOR is expressed in progenitors and in immature oligodendrocytes, but not in mature oligodendrocytes. This suggests that MOR could be involved in some developmental process of the cells of the oligodendroglial lineage.

In situ expression of PLP/DM-20, MBP, and CNP during embryonic and postnatal development of the jimpy mutant and of transgenic mice overexpressing PLP

We analyzed by in situ hybridization the spatiotemporal expression of dm-20, myelin basic protein (MBP) and 2'-3' cyclic nucleotide phosphodiesterase (CNP) during embryonic and postnatal development of the normal mouse and two plp/dm-20 mutants: the jimpy mouse and a transgenic mouse overexpressing the plp gene. In the central nervous system (CNS) of the normal mouse, dm-20 mRNA was detected at embryonic day (E)9.5 in the laterobasal plate of the diencephalon. The pattern of expression of CNP transcript was superimposable on that of dm-20, but appeared slightly later, at E12.5. MBP mRNA was detected even later (E14.5), and, in addition, only in the caudal (rhombencephalon and spinal cord) territories of expression of dm-20 and CNP. These observations support our previous proposals: (1) dm-20-expressing cells in the germinative neuroepithelium are precursors of oligodendrocytes, and (2) oligodendrocytes emerge from distinct pools of precursors along the neural tube (Timsit et al., 1995). In the jimpy mutant, despite the mutation in the plp gene, cells of the oligodendrocyte lineage developed normally. It is only at the time of myelin deposition that oligodendrocytes die. During embryonic development of the transgenic mutant overexpressing plp, there were no alterations in the spatiotemporal pattern or the level of expression of dm-20 in the CNS, in contrast to the higher levels of dm-20 observed in the peripheral nervous system (PNS).

Temperature-dependent regulation of PLP/DM20 and CNP gene expression in two conditionally-immortalized jimpy oligodendrocyte cell lines

We conditionally immortalized jimpy primary oligodendrocytes (ODCs) with the temperature-sensitive SV40 large T antigen. Two cell lines (clones JP1.1 and JP1.2) were generated that expressed a number of ODC markers. Both jimpy cell lines expressed DM20 mRNAs at the proliferative temperature of 34 degrees C, but not at the "differentiation" temperature of 39 degrees C. Interestingly, at 39 degrees C neither cell line appeared to differentiate further, and neither survived longer than 7 days, in contrast to other ODC cell lines from normal animals that survive many weeks at 39 degrees C. These findings are not consistent with the notion that a PLP/DM20 gene product is the cause of oligodendrocyte cell death in jimpy, since neither jimpy cell line survived at 39 degrees C, and neither line expressed PLP or DM20 proteins. Analysis of the expression of the CNP (2'3' cyclic nucleotide-3'-phosphodiesterase) gene indicated that in both cell lines only one of the two CNP isoforms was expressed at 34 degrees C. Raising the temperature to 39 degrees C caused a greater reduction in the levels of CNP protein than CNP mRNA. Taken together, the DM20 and CNP data suggest that at least some of the decline in myelin/oligodendrocyte components observed in jimpy brains may not be due simply to fewer mature oligodendrocytes, but also to a down regulation of expression of these genes at several levels including transcriptional and post-transcriptional events. Our results provide two cell models for in vitro investigations into the nature of the jimpy mutation at several cellular and molecular levels.

A 39-kD DNA-binding protein from mouse brain stimulates transcription of myelin basic protein gene in oligodendrocytic cells

The MB1 regulatory sequence of the myelin basic protein (MBP) gene spanning between nucleotides -14 to -50 with respect to the transcription start site is critical for cell type-specific transcription of the MBP gene, which encodes the major protein component of myelin sheath in cells derived from the central nervous system (CNS). This regulatory sequence has the ability to interact with a developmentally controlled DNA-binding protein from mouse brain that stimulates transcription of MBP promoter in an in vitro system (Haas, S., J. Gordon, and K. Khalili. 1993. Mol. Cell. Biol. 13:3103-3112). Here, we report the purification of a 39-kD protein from mouse brain tissue at the peak of myelination and MBP production that binds to the MB1 regulatory motif. Following partial amino acid sequence analysis, we have identified a complementary DNA encoding a 39-kD DNA-binding protein called pur alpha. Expression of pur alpha cDNA in the prokaryotic and eukaryotic cells resulted in the synthesis of a protein with characteristics similar to the purified brain-derived 39-kD protein in band shift competition assays. Cotransfection of the recombinant pur alpha expressor plasmid with MBP promoter construct indicated that Pur alpha stimulates transcription of the MBP promoter in oligodendrocytic cells, and that the nucleotide sequence required for binding of the 39-kD Pur alpha to DNA within the MB1 region is crucial for this activity. Moreover, transient expression of Pur alpha caused elevation in the level of endogenous MBP RNA in oligodendrocytic cells. Thus, Pur alpha, a sequence-specific DNA-binding protein upon binding to MB1 regulatory region may play a significant role in determining the cell type-specific expression of MBP in brain.

Basic fibroblast growth factor down-regulates myelin basic protein gene expression and alters myelin compaction of mature oligodendrocytes in vitro

The effects of basic fibroblast growth factor (bFGF) on myelin basic protein (MBP) gene expression and myelin-like membrane formation were investigated in oligodendrocyte cultures containing mainly mature oligodendrocytes expressing MBP. These cultures were obtained by selective detachment of the cells of the oligodendrocyte lineage from 40-day-old mixed cultures derived from newborn rat brain. They were further purified by a 3-day pretreatment with cytosine arabinoside (ARA-C) in order to kill cycling cells. After withdrawal of ARA-C, daily treatment of the cells with bFGF for 3 days induced a drastic decrease in MBP mRNA level compared to control cultures treated only with ARA-C. Moreover, the percentage of oligodendrocytes labelled with anti-MBP antibodies decreased by 50%, as well as that of oligodendrocytes expressing myelin oligodendrocyte glycoprotein (MOG), whereas proteolipid protein (PLP) immunolabelled cells were less affected. At the ultrastructural level, myelin-like membranes were still abundant in the ARA-C- and bFGF-treated cultures, but they were conspicuously uncompacted compared to cultures only pretreated with ARA-C. These results bring the first evidence that bFGF is able to down-regulate myelin protein gene expression in mature oligodendrocytes and to alter myelin structure. They imply that if bFGF is secreted after a demyelinating lesion of the central nervous system (CNS), this plasticity of mature oligodendrocytes will allow final remyelination of axons to complete only after this factor has returned to low levels.

Cellular influences on RNA sorting in neurons and glia: an in situ hybridization histochemical study

The unique structures of process-bearing cells in the central nervous system (CNS) present an ideal model with which to study the differential distribution of mRNA. We conducted a side-by-side examination of the intracellular distribution of nine neural mRNAs by in situ hybridization histochemistry in mammalian brain and observed four general types of mRNA distributions. (1) Some mRNA species were confined to cell somas and included those encoding the glial proteins, myelin proteolipid protein and 2'3'-cyclic nucleotide-3'-phosphodiesterase and the neuronal enzymes, neuron-specific enolase and glutamate decarboxylase-67. (2) Some mRNAs were found abundantly within the cell soma and were also located throughout cellular processes. These included myelin basic protein (MBP) mRNA, which was localized to the cell soma and myelin sheaths of oligodendrocytes, and glial fibrillary acidic protein (GFAP) mRNA, which was localized to the cell soma and processes of reactive and some non-reactive astrocytes in the adult brain and radial glia in embryonic brain. (3) Some mRNAs were found primarily in perinuclear cytoplasm but in some cells were also observed in cell processes. These included mRNAs encoding the protein kinase C/calmodulin-binding substrates, RC3 (neurogranin) and GAP-43, which were identified in the somas as well as within the proximal dendritic branches of specific forebrain neurons. (4) Some mRNAs were localized primarily within cell processes. These included MAP2 mRNA, which was identified by deep staining within dendritic fields but by only light staining within neuronal cell bodies. The data also indicated that the stage of cellular development and the regional location of a cell within the CNS had a profound influence on translocation events. MAP2 mRNA was found in the dendritic processes of most neurons but was confined to the soma of neurons in specific brainstem nuclei. MBP mRNA was confined to the perinuclear cytoplasm of immature oligodendrocytes and was then transported into the myelin sheath at a developmental stage corresponding to myelination. The distribution patterns of these mRNAs are likely to reflect the mechanism by which the protein products of these molecules are targeted within neurons and glia. In addition, mRNA movement may be influenced by cellular and regional factors not encoded solely within the structure of the translocated mRNA.

Myelin in multiple sclerosis is developmentally immature

The etiology of multiple sclerosis (MS) is considered to involve genetic, environmental, infective, and immunological factors which affect the integrity of a normally assembled myelin sheath, either directly or indirectly resulting in demyelination. In a correlative study involving protein chemical, mass spectrometric, and electron microscopic techniques we have determined that myelin obtained from victims of MS is arrested at the level of the first growth spurt (within the first 6 yr of life) and is therefore developmentally immature. The data supporting this conclusion include (a) the pattern of microheterogeneity of myelin basic protein (MBP); (b) the NH2-terminal acylation of the least cationic component of MBP ("C-8"); (c) the phase transition temperature (Tc) of myelin isolated from victims of MS correlated with the increased proportion of the least cationic component of MBP; and (d) immunogold electron microscopy using an antibody specific for "C-8" showed that the distribution of gold particles in a 2-yr-old infant was similar to the distribution found in a victim of MS. We postulate that this developmentally immature myelin is more susceptible to degradation by one or a combination of factors mentioned above, providing the initial antigenic material to the immune system.

Structural features of myelin basic protein mRNAs influence their translational efficiencies

The myelin basic protein (MBP) gene expresses several alternatively spliced products with the same 5' and 3' untranslated regions (UTRs). It has been reported that its expression may be regulated not only at the transcriptional level but also at the translational level during development. We engineered several MBP mRNA deletion mutants with 5' (-48, -37, -27, -22, and -10) and 3' UTRs of differing lengths and examined the translational efficiencies of these constructs in cell-free systems. The translational efficiencies of the constructs differed significantly over a range of almost 10-fold. A deletion of 11 nucleotides from the 5' end of the natural (i.e., -48) MBP mRNA resulted in an approximate fourfold reduction in translational efficiency. Further truncation of the 5' UTR increased the translational efficiencies of the constructs as has been observed with many RNAs. These results suggest that there may be a positive control element between -48 and -37 nucleotides in the 5' UTR of MBP mRNA. The effects of modifying the lengths of the 5' UTR on the translational efficiency of mRNAs encoding the 21.5-kDa and 14-kDa MBPs were the same, suggesting that the effect observed was not unique to the 21.5-kDa MBP mRNA. Truncating the 3' UTR of four different alternatively spliced MBP mRNAs also altered their translational efficiencies. Thus, the 5' and 3' UTRs of MBP mRNAs appear to influence the translation of these mRNAs, and such factors may be involved in the translational regulation of MBP gene expression.

Myelin basic protein mRNA translocation in oligodendrocytes is inhibited by astrocytes in vitro

Myelin basic protein (MBP) mRNAs are translocated from cell bodies into the slender processes connecting oligodendrocyte somas with the myelin sheath in vivo. This translocation was observed in mixed glial cultures prepared from newborn mouse brains and it occurred in approximately 25% of the cells expressing the gene. However, when "enriched" oligodendrocytes were prepared by shaking them free of other glial cells, MBP mRNA translocation occurred into the processes of essentially all of the cells. When enriched oligodendrocytes were plated back onto astrocytes, MBP mRNA was observed to be confined to the cell bodies of almost all the cells, indicating a marked inhibition of translocation of the mRNA. This inhibition of mRNA translocation did not appear to be mediated through soluble factors secreted by astrocytes or by "astromatrix," but rather through physical contact between the oligodendrocytes and astrocytes. Intact, but not necessarily live, astrocytes were required for the inhibition of mRNA translocation in the oligodendrocytes. Fibroblasts and a neuroblastoma cell line, SKN-SH, did not inhibit MBP mRNA translocation in oligodendrocytes suggesting that astrocyte surface-specific components might be involved in the interaction between astrocytes and oligodendrocytes in culture. These results suggest that contact between these two cell types can influence intramolecular events related to myelinogenesis.

Expression of myelin protein genes and other myelin components in an oligodendrocytic cell line conditionally immortalized with a temperature-sensitive retrovirus

We have conditionally immortalized oligodendrocytes isolated from normal and shiverer primary mouse brain cultures through the use of the retroviral vector ZIPSVtsA58. This vector encodes an immortalizing thermolabile simian virus 40 large T antigen (Tag) and allows for clonal selection by conferring neomycin (G418) resistance. We isolated 14 shiverer and 10 normal lines that expressed the early oligodendrocyte marker 2',3'-cyclic nucleotide 3'-phosphodiesterase mRNA. These cell lines grew continuously at the permissive temperature (34 degrees C) and displayed Tag nuclear immunostaining. On shifting to nonpermissive temperatures (39 degrees C), the cells showed rapid arrested cell growth and loss of Tag staining. One line (N20.1) engineered from normal oligodendrocytes also expressed myelin basic protein (MBP) and proteolipid protein (PLP) mRNAs, genes normally expressed by mature, differentiated oligodendrocytes. No differences in any of the myelin-specific protein mRNA levels were observed in N20.1 cells grown at 39 degrees C for > 9 days compared with cells maintained at 34 degrees C. Immunocytochemical staining revealed N20.1 cells to be positive for the oligodendrocyte surface markers--galactocerebroside, A007, and A2B5. However, MBP and PLP polypeptides could not be detected by western blot or immunocytochemical staining at either the permissive or nonpermissive temperature. Cell-free protein synthesis experiments indicated that the MBP mRNAs isolated from N20.1 cells were translatable and directed the synthesis of the 17-, 18.5-, and 21.5-kDa MBP isoforms. Analysis of the PLP/DM20 gene splice products by polymerase chain reaction indicated that the expression of DM20 mRNA predominated over that of PLP mRNA in this cell line. Because the cell line expressed the MBP and PLP genes, it represents a "mature" oligodendrocyte, but the splicing patterns of these genes indicate that it is at an early stage of "maturation." This cell line has now been passaged > 40 times with fidelity of phenotype and genotype.

Extracellular somatostatin measured by microdialysis in the hippocampus of freely moving rats: evidence for neuronal release

Intracerebral microdialysis combined with a sensitive and specific radioimmunoassay was used to monitor the neuronal release of somatostatin (somatostatin-like immunoreactivity, SLI) in the dorsal hippocampus of freely moving rats. The sensitivity of the radioimmunoassay was optimized to detect < 1 fmol/ml. The basal concentration of SLI in 20-min dialysate fractions (5 microliters/min) collected 24 h after probe implantation was stable over at least 200 min. The spontaneous efflux dropped by 54 +/- 6.4% (p < 0.05) when Ca2+ was omitted and 1 mM EGTA added to the Krebs-Ringer solution and by 65.5 +/- 3.2% (p < 0.05) in the presence of 1 microM tetrodotoxin. Depolarizing concentrations of the Na+ channel opener veratridine (6.25, 25, 100 microM) induced 11 +/- 2 (p < 0.05), 17 +/- 2 (p < 0.05), and 21 +/- 5 (p < 0.01) fold increase in SLI concentration, respectively, during the first 20 min of perfusion. The effect of 100 microM veratridine was blocked by coperfusion with 5 microM tetrodotoxin (p < 0.01) and reduced by 79% (p < 0.01) in the virtual absence of Ca2+. Neuronal depolarization by 20 min of perfusion with Krebs-Ringer solution containing 25 and 50 mM KCl and proportionally lowered Na+ increased the dialysate SLI 4.4 +/- 1 (p < 0.05) and 17 +/- 3 (p < 0.01) fold baseline, respectively. Ten micromolar ouabain, a blocker of Na+,K(+)-ATPase, increased the dialysate SLI 15-fold baseline, on average (p < 0.05), during 80 min of perfusion. The results demonstrate the suitability of brain microdialysis for monitoring the neuronal release of SLI and for studying its role in synaptic transmission.

Isolation and sequence determination of cDNA encoding PMP-22 (PAS-II/SR13/Gas-3) of human peripheral myelin

A full length cDNA of PMP-22 (PAS-II/SR13/Gas-3) of peripheral myelin has been isolated from a cDNA library of human fetus spinal cord. The clone is 1823 base pairs (bp) in length and contains a 480 bp open reading frame encoding a polypeptide of 160 residues. The deduced amino acid sequence is highly homologous to PMP-22 from bovine (PAS-II), rat (SR13) and mouse (Gas-3).

Characterization of a cell line derived from a human oligodendroglioma

A novel clonal cell line derived from a human glioma (HOG) was found to express some oligodendrocyte-specific proteins including a 15-kDa form of myelin basic protein (MBP) and high 2',3'-cyclic nucleotide 3'-phosphodiesterase (CNPase) activity. Expression of the myelin lipids galactosylceramide and sulfogalactosylceramide (sulfatide) was low. HOG cells did not express the characteristic astrocyte markers glial fibrillary acidic protein (GFAP) or significant glutamine synthetase (GS) activity. After initial plating, HOG cells were flat and epitheloid and thus showed a limited oligodendrocyte-like morphology. However, after cells became more confluent, some cells were phase-bright and elaborated short processes. Receptor types expressed by HOG cells included A2-adenosine, prostaglandin E1 (PGE1), and beta 2-adrenergic receptors (beta-ARs) linked to stimulation of adenylate cyclase, and muscarinic cholinergic and H1-histamine coupled to phosphatidyinositol turnover (Post and Dawson, 1991). HOG cells should therefore provide a useful model for studying the extracellular regulation and phosphorylation of oligodendrocyte-specific proteins.

Isolation and sequence determination of cDNA encoding P2 protein of human peripheral myelin

A full length cDNA of P2 protein of peripheral myelin has been isolated from a cDNA library of human fetus spinal cord. The clone is 2150 base pairs (bp) in length and contains a 393 bp open reading frame encoding a polypeptide of 131 residues. The deduced amino acid sequence is highly homologous to P2 protein from other species.

Isolation and sequence determination of cDNA encoding the major structural protein of human peripheral myelin

A full length cDNA of the major structural protein of peripheral myelin (P0 protein) has been isolated from a cDNA library of human fetus spinal cord. The clone is 1948 base pairs (bp) in length and contains a 744 bp open reading frame encoding a polypeptide of 248 residues including 29 signal peptide. The deduced amino acid sequence is highly homologous to P0 protein from other species.

Morphological, biochemical, and functional characterization of bulk isolated glial progenitor cells

We describe a simple, rapid, and efficient method, based on separation on a Percoll centrifugation gradient, to purify glial progenitor cells from newborn rat brains. Cytofluorimetry analysis of the isolated cell population showed that 75 +/- 8 and 86 +/- 7% of the cells were A2B5- and R24-positive, respectively. Transmission electron microscopy examination of the purified cell population confirmed their homogeneity and illustrated their typical morphology, as previously described in situ. Assay of UDP-galactose-ceramide galactosyltransferase, 3'-phosphoadenosine 5'-phosphosulfate galactosylceramide sulfotransferase, and 2',3'-cyclic nucleotide 3'-phosphohydrolase activities showed that the levels of these enzymes were 446, 76, and 11 times lower, respectively, than the levels measured in mature oligodendrocytes. Low levels of mRNA coding for 2',3'-cyclic nucleotide 3'-phosphohydrolase and myelin proteolipid protein, but not for myelin basic protein, were present in the glial progenitor cells. At the time of isolation, 40% of the cells in the population were dividing, and the cells could easily be expanded in culture. After 3 weeks of culture in the presence of 1% fetal calf serum, 75% of the cells had differentiated into galactosylceramide-positive oligodendrocytes. When the culture took place in the presence of 10% fetal calf serum, only 2% of the cells expressed galactosylceramide, and 60% were glial fibrillary acidic protein-positive astrocytes; half of them were also A2B5 positive.

Nuclear proteins in mouse brain cells bind specifically to the myelin basic protein regulatory region

Expression of myelin basic protein (MBP) in mice is regulated in a cell- and stage-specific manner during brain development. The MBP control region contains multiple cis-acting elements, shown by in vivo and in vitro assays, which are responsible for its unique pattern of transcription. Using synthetic DNA fragments spanning the MBP control region, we have analyzed nuclear proteins obtained from newborn (2-3 d), young adult (18-30 d), and adult (60 d) animals; these nuclear proteins form DNA-protein complexes with the MBP regulatory region. Brain extracts from young adult and adult mice showed enhanced binding activities with the sequences supporting transcriptional activation in glial cells. Deletion analysis of the proximal activating sequence located at position -14 to -50 with respect to the RNA initiation site resulted in identification of a small region, located between nucleotides -14 to -37, which is required for formation of the complexes. Southwestern assay revealed a major 39-kD protein from young adult brain extract that recognizes the sequences between nucleotides -14 to -37. An additional minor 37-kD protein, derived from young adult brain extract, was also found to be associated with this proximal activating region. Of particular interest is the observation that the minor 37-kD protein became more abundant in the extract derived from adult brain, whereas the major 39-kD protein became less abundant. The possible role of these proteins in cell/stage-specific transcription of MBP is discussed.

Expression of a novel transcript of the myelin basic protein gene

A cDNA (M41) corresponding to a mouse myelin basic protein (MBP) mRNA with a longer 5'-untranslated region than predicted from earlier studies of MBP gene structure has been isolated and characterized. The additional 5'-untranslated region is encoded by two previously unidentified exons upstream of the major transcription start site of the gene. Using a DNA probe specific for M41-MBP mRNAs, Northern blot analysis indicated that expression of this transcript follows a developmental course in mouse brain similar to that of the majority of MBP mRNAs, but that the level of expression varies between brain and spinal cored. Expression of MBP mRNAs similar to the mouse M41-MBP also was identified in rat brain. The results suggest that the structure of the MBP gene is more complex than originally thought, containing at least two more exons. There appears to be at least one more MBP gene promoter that directs the synthesis of a subset of MBP mRNAs with a unique 5'-untranslated region.

Role of phosphorylation in conformational adaptability of bovine myelin basic protein

Controlled thrombic digestion of a preparation of components 2 + 3 isolated from the 18.5 kDa bovine myelin basic protein (MBP) yielded a polypeptide that was monophosphorylated on threonine 97 (component 3pT97). This is the first posttranslationally phosphorylated MBP isolated in pure form. We studied the effect of this single phosphate on the conformational adaptability of 18.5 kDa bovine MBP by comparing the circular dichroism (CD) spectrum of component 3pT97 with the spectra of highly purified nonphosphorylated components 1 and 2. The CD spectra of nonphosphorylated component 1 and component 2 [monodeamidated form(s) of component 1] were indistinguishable, while component 3pt97 exhibited a different spectrum. The singly phosphorylated MBP component exhibited 13% more ordered conformations than that adopted by nonphosphorylated MBP in dilute aqueous solutions. This was estimated from the CD spectra, and apparently involved about 17 additional amino acid residues in beta-structure(s).

Developmental expression of myelin proteolipid, basic protein, and 2',3'-cyclic nucleotide 3'-phosphodiesterase transcripts in different rat brain regions

RNA was extracted from five different rat brain regions during development, starting from embryonic day 15 (E15) until postnatal day 60 (P60). These RNA preparations were analyzed by both Northern and dot blot for their content of 2',3'-cyclic nucleotide 3'-phosphodiesterase (CNPase), myelin proteolipid protein (PLP), and myelin basic protein (MBP) -specific transcripts. CNPase mRNA was readily detectable at E15 and PLP mRNA at P1 in all brain regions examined. In contrast, expression of MBP mRNA followed a caudorostral gradient. It was first observed at P1 in the mesencephalon and at P9-P11 in the olfactory bulb. Expression of these three transcripts displayed two types of developmental profiles. One was termed biphasic because the specific mRNA level increased regularly and then reached a plateau level. The other developmental profile was termed triphasic, because there was a gradual increase in the level of specific transcripts with a sudden appearance of a sharp peak followed by a decline to a plateau level. When the triphasic pattern was observed, the date of the peak appearance was probe-, but not region-, dependent. It was P15 for CNPase, P18 for MBP, and P21 for PLP. As these peaks occurred at a time during development when myelination was the most active, we postulate the existence of a transient external signal, perhaps neuronal, which would be responsible for this increased amount of myelin-related transcripts.

Regional expression of myelin protein genes in the developing mouse brain: in situ hybridization studies

Expression of mRNAs for the two major myelin proteins, myelin basic protein (MBP) and proteolipid protein (PLP), was examined in a number of regions of the developing mouse brain using in situ hybridization. In general, MBP and PLP mRNAs were observed to be coexpressed during ontogeny, prior to the histological appearance of myelin. Expression of both mRNAs was detected as early as 6 hours postpartum in the medulla oblongata and, with development, expression of these mRNAs progressed in a caudal to rostral direction. Peak expression occurred at approximately postnatal day 20 in most regions examined, regardless of time of onset of expression. As myelination proceeded, two different labeling patterns were observed with the PLP and MBP 35S-labeled cDNA probes. In the earliest stages of myelinogenesis MBP mRNA labeling was restricted to oligodendrocyte cell bodies, but shortly after the gene began to be expressed the labeling became more diffuse. In contrast, PLP mRNA labeling remained over or surrounding oligodendrocyte cell bodies at all stages of myelinogenesis. These two distinctly different patterns of labeling are consistent with alternative intracellular trafficking of MBP and PLP mRNAs, in which PLP mRNAs remain associated with ribosomes within the cell soma and MBP mRNAs move from the cell soma to the oligodendrocyte processes at a specific stage early in myelinogenesis. However, there appeared to be a clear time lag between the onset of MBP mRNA expression and the movement of ribosomes carrying MBP mRNAs into the oligodendrocyte processes. Additionally, the in situ hybridization studies revealed a population of unidentified cells residing in cortical molecular layers that express PLP mRNA in the absence of MBP mRNA.

An approach to searching protein sequences for superfamily relationships or chance similarities relevant to the molecular mimicry hypothesis: application to the basic proteins of myelin

A rapid method for similarity searches (FASTP program) was used to identify similarities between a protein database and the human basic proteins from myelin [P2 protein and 17.2K, 18.5K, and 21.5K variants of myelin basic protein (MBP)]. From similarity scores, we concluded that none of the presently known proteins are in a family containing the MBPs. No new members were found for the lipid-binding family of which P2 is a member. Sequence similarities deemed relevant to the molecular mimicry hypothesis for virus-induced autoimmunity were identified in FASTP data with the aid of microcomputer programs. Several MBP/viral protein similarities were found that have not been reported previously. Of note because of their association with demyelinating conditions were proteins from visna and vaccinia. Similarity with visna was specific to the 21.5K and 20.2K MBPs. The most interesting new possibility for mimicry involving the P2 protein was between the influenza A NS2 protein and a sequence region of P2 thought to be neuritogenic in animals and mitogenic for lymphocytes from some patients with Guillain-Barré syndrome (GBS). This may have relevance for some cases of GBS associated with the 1976 U.S.A. swine flu vaccination program. Because FASTP reports only the best similarities between proteins, searches with FASTP may not have detected all the examples of mimicry present in the database. Searches might also be more effective if similarities could be scored on immunological rather than structural relatedness.

Molecular biology of myelin proteins from the central nervous system

Within the past several years, several of the genes coding for the major myelin proteins have been isolated, characterized, and mapped to specific chromosomes. In all cases, it has been clearly established that these proteins exist as multiple isoforms, and their structures have been established through an analysis of the cDNA clones encoding them. In each case, the isoforms appear to arise through the translation of individual mRNAs produced by alternative splicing of the primary transcript of a single gene. In several cases, the expression of the individual isoforms appears to be developmentally and/or regionally regulated, probably at the level of the splicing of the primary transcript. In the case of the dysmyelinating mutants shiverer and jimpy, the molecular defects involve the MBP gene and PLP gene, respectively; most of the dysmyelinating mutants, including those in which the genetic defect is established, appear to exhibit pleiotropy with respect to the expression of other myelin protein genes.

Cellular and molecular aspects of myelin protein gene expression

The cellular and molecular aspects of myelin protein metabolism have recently been among the most intensively studied in neurobiology. Myelination is a developmentally regulated process involving the coordination of expression of genes encoding both myelin proteins and the enzymes involved in myelin lipid metabolism. In the central nervous system, the oligodendrocyte plasma membrane elaborates prodigious amounts of myelin over a relatively short developmental period. During development, myelin undergoes characteristic biochemical changes, presumably correlated with the morphological changes during its maturation from loosely-whorled bilayers to the thick multilamellar structure typical of the adult membrane. Genes encoding four myelin proteins have been isolated, and each of these specifies families of polypeptide isoforms synthesized from mRNAs derived through alternative splicing of the primary gene transcripts. In most cases, the production of the alternatively spliced transcripts is developmentally regulated, leading to the observed protein compositional changes in myelin. The chromosomal localizations of several of the myelin protein genes have been mapped in mice and humans, and abnormalities in two separate genes appear to be the genetic defects in the murine dysmyelinating mutants, shiverer and jimpy. Insertion of a normal myelin basic protein gene into the shiverer genome appears to correct many of the clinical and cell biological abnormalities associated with the defect. Most of the dysmyelinating mutants, including those in which the genetic defect is established, appear to exhibit pleiotropy with respect to the expression of other myelin genes. Post-translational events also appear to be important in myelin assembly and metabolism. The major myelin proteins are synthesized at different subcellular locations and follow different routes of assembly into the membrane. Prevention of certain post-translational modifications of some myelin proteins can result in the disruption of myelin structure, reminiscent of naturally occurring myelin disorders. Studies on the expression of myelin genes in tissue culture have shown the importance of epigenetic factors (e.g., hormones, growth factors, and cell-cell interactions) in modulating myelin protein gene expression. Thus, myelinogenesis has proven to be very useful system in which to examine cellular and molecular mechanisms regulating the activity of a nervous system-specific process.

Electroimmunoblotting of myelin basic protein peptides: a novel approach to the rapid characterisation of antigenic specificities of monoclonal and polyclonal anti-MBP antibodies

A rapid and sensitive method for the identification of antigenic determinants recognised by monoclonal and polyclonal antibodies directed against myelin basic protein (MBP) is described. By electroimmunoblotting a series of overlapping peptides covering the entire MBP molecule with monoclonal anti-MBP antibodies, the binding pattern of immunoreactive peptides can be rapidly determined and the reactive antigenic determinant identified. This procedure, which can be performed with both native and synthetic peptides, can also with appropriate modification, be applied to the analysis of naturally occurring or experimentally induced polyclonal anti-MBP autoantibodies.

Myelin composition and activities of CNPase and Na+,K+-ATPase in hypomyelinated "pt" mutant rabbit

A disorder of CNS myelination was found in paralytic tremor ("pt") rabbits. The condition is inherited in a sex-linked recessive mode. Ultrastructurally, an obvious myelin deficiency with aberration of myelin sheath formation is observed. The yield of myelin isolation was reduced to 20-30% of control. Myelin isolated from 4-week-old "pt" rabbits contained reduced amounts of galactosphingolipids and of several myelin protein markers. Moreover, myelin basic protein, analyzed by two-dimensional gel electrophoresis, showed a deficit in its more basic components. All these facts suggest a delay in myelin maturation. Ganglioside content was increased as well as Na+,K+-ATPase specific activity. 2',3'-Cyclic nucleotide phosphodiesterase (CNPase) specific activity was the same in "pt" as in control myelin but differed by having greater sensitivity to detergent activation.

Developmental expression of the myelin proteolipid protein and basic protein mRNAs in normal and dysmyelinating mutant mice

Expression of the myelin proteolipid protein (PLP) was examined in the nuclei and polysomes of 12-27-day-old quaking, jimpy, and shiverer mouse brains and in 2-27-day-old normal brains and compared with expression of the myelin basic proteins (MBPs). Northern blots showed the presence of multiple mouse PLP RNAs, the developmental expression of which coincided with myelination. Two major mouse PLP RNAs, 3.5 and 2.6 kilobases in length, were observed in both cytoplasmic polyribosomes and nuclei, and, in addition, a larger 4.6-kilobase PLP RNA was observed in nuclei. Quantitative measurements with slot blot analyses showed that the levels of PLP and MBP RNAs peaked simultaneously at 18 days in nuclei but that maximal levels of PLP RNA lagged behind MBP RNA by several days in the polysomes. The developmental expression of both major classes of myelin protein mRNAs was affected in all three mutants. In shiverer brains, the levels of PLP mRNA in polysomes and nuclei were only 30-55% of control levels after 15 days. Thus, the deletion of a portion of the MBP gene appeared to have a major effect on the expression of the PLP gene in this mutant. In jimpy mice, where the mutation has been shown to involve the PLP gene, expression of MBP mRNA was also severely reduced, to less than 25% of control values. In quaking brains, the expression of each gene followed its own developmental course, different from each other and different from the normal mouse. The extent to which the expression of PLP and MBP was affected by the quaking mutation depended on the age at which it was examined.

Identification of a cDNA coding for a fifth form of myelin basic protein in mouse

The primary sequences of four molecular mass variants (14, 17, 18.5, and 21.5 kDa) of the mouse myelin basic protein (MBP) have recently been determined through analysis of cDNA clones of their mRNAs. The mRNAs coding for the four MBP variants are thought to arise by differential splicing of two exons (exons 2 and 6) from a single gene. In contrast, exons 2 and 5 may be spliced out in the posttranscriptional processing of the human MBP gene. To investigate the possibility that a third exon (exon 5) may also be differentially spliced out in the processing of the mouse MBP gene transcript, a mouse cDNA library was screened to search for cDNAs missing exon 5. A MBP cDNA was isolated whose coding region specified a fifth mouse MBP variant with a molecular mass of approximately equal to 17 kDa. The mass of this variant (17,257 Da) is so close to that of the other 17-kDa mouse MBP (17,224 Da) that the two would be indistinguishable on NaDodSO4/polyacrylamide gels. Analysis of the sequence of the cDNA clone indicates that excision of exons 2 and 5 of the mouse MBP gene would produce the mRNA encoding this newly described 17-kDa MBP, whereas excision of exon 6 would produce the mRNA for the other 17-kDa MBP variant. Thus, the "17-kDa" mouse MBP consists of at least two molecular forms with very similar molecular masses but markedly different primary sequences. Of five full-length or near full-length cDNAs representing 17-kDa MBPs, one was missing exons 2 and 5 and four were missing exon 6.

Assignment of the myelin basic protein gene to human chromosome 18q22-qter

The assignment of the human myelin basic protein gene to 18q22-qter has been made using a mouse cDNA probe in the study of human-mouse somatic cell hybrids and by in situ hybridization. These results confirm the earlier assignment using in situ studies alone by Saxe et al. (1985).

Investigations on myelinogenesis in vitro: developmental expression of myelin basic protein mRNA and its regulation by thyroid hormone in primary cerebral cell cultures from embryonic mice

The concentration of myelin basic protein (MBP) mRNA in primary cultures of cells dissociated from embryonic mouse cerebra and grown in the presence of varying amounts of thyroid hormone was measured using a 32P-labeled cDNA probe and a dot-blot procedure. The cDNA probe contained 1.85 kilobases of the gene for MBP. The concentration of mRNA specific for MBP in control cells grown on a medium containing normal (euthyroid) calf serum increased with increasing age of culture. The greatest increase occurred between 15 and 35 days in culture (5.25-fold increase); whereas between 35 and 50 days in culture, the rate of accumulation slowed to yield a net increase of MBP mRNA of only 10%. The quantity of MBP mRNA was drastically diminished at all ages studied when the cells were grown from the sixth day onward on a medium containing hypothyroid calf serum. Although the amount of MBP mRNA in hypothyroid-treated cells did increase, the change in concentration was less (3.43-fold), and it peaked earlier (at 30 days). Unlike the euthyroid cells, after 30 days the MBP mRNA actually fell in the hypothyroid-treated cells. If hypothyroid media were supplemented with triiodothyronine (T3) on the eighth day in culture, the quantity of MBP mRNA in the cells was restored almost completely to the levels found in the control euthyroid cells at all ages. Therefore, the regulation of the synthesis of MBP by thyroid hormone is at least in part a pretranslational event; that is, thyroid hormone adjusts the concentration of the mRNA specific for MBP.

Evidence for the expression of four myelin basic protein variants in the developing human spinal cord through cDNA cloning

Four human myelin basic protein (MBP) variants with molecular masses of 21.5, 20.2, 18.5, and 17.3 kilodaltons (kDa) have been identified in the developing human spinal cord and their structures determined through an analysis of cDNA clones of their mRNAs. The 20.2-kDa MBP mRNA encoded a novel MBP variant, the structure of which has not been reported in any species. Its amino acid sequence was identical with that of the 21.5-kDa MBP except for a deletion of 11 amino acid residues encoded by exon 5 of the MBP gene. All four human MBP variants were identical except for the insertion of deletion of two peptide fragments corresponding to those encoded by exons 2 and 5 of the MBP gene. In this study, no mature human MBP cDNAs missing exon 6 sequences were identified. This suggests that, unlike the mouse, the four human MBP mRNAs encoding these MBP variants arise by the alternative splicing of only exons 2 and 5 from the primary MBP gene transcript. This indicates that the predominant MBP splicing pathways in human and mouse are different. Immunoblots of human fetal spinal cords (11-21 weeks) indicated that MBP expression turned on abruptly between 14 and 16 weeks. Expression of the 20.2-kDa MBP variant was most evident at 16 weeks and its relative proportion declined thereafter, suggesting that its expression was developmentally regulated.

Structure and expression of the mouse myelin proteolipid protein gene

The gene for the mouse myelin proteolipid protein has been isolated and the seven exons have been sequenced. Since the sequence of a rat proteolipid protein cDNA and partial sequence of the human proteolipid protein gene have been determined, it was possible to demonstrate a very high degree of conservation for the proteolipid protein gene exons among species. While there are some nucleotide changes, the protein coding region of the mouse gene encodes protein that is totally conserved relative to both rat and human proteolipid proteins. The regulatory and noncoding regions of the proteolipid protein gene are also highly conserved. The upstream regulatory and 5'-noncoding region of the gene is 92% homologous to the comparable region of the human proteolipid protein gene, and the 3'-noncoding region of the mouse gene is approximately 90% homologous to a rat proteolipid protein cDNA through 2,200 nucleotides of 3'-noncoding DNA. S1 nuclease protection experiments indicated that the major 5'-end for proteolipid protein mRNAs from mouse, rat, human, or baboon is approximately 147-160 nucleotides upstream from the initial methionine codon of the protein coding region. Other S1 nuclease protection experiments indicated the possible existence of an alternative splice site within exon 3, which may produce mRNA for DM20. This mRNA is approximately 100 nucleotides shorter than that for the proteolipid protein, and it is missing the latter half of exon 3, that is, amino acids 116-150 of the proteolipid protein sequence.

Expression of myelin proteins in the developing human spinal cord: cloning and sequencing of human proteolipid protein cDNA

A full-length clone for the human proteolipid protein (PLP) was isolated from a cDNA library constructed from poly(A)+ RNA isolated from fetal spinal cords obtained at 15-24 weeks of conceptional age. The sequence of the human PLP cDNA was determined, and the deduced amino acid sequence was found to be identical with that of rat PLP. Comparison of human and rat PLP cDNA clones indicated that the coding regions retained 97% homology and that there were also other areas of conserved sequence. The human 5'-untranslated region was 93% homologous to that of the rat. The 3'-untranslated region was, overall, 73% homologous to that of the rat with areas containing greater than 84% homology in the first 400 and last 200 nucleotides. The most variability within the 3'-untranslated region occurred between nucleotides 2,000-2,500, where homology with the rat cDNA dropped to 55%. Expression of PLP in the human spinal cord between 11 and 23 weeks after conception was examined and compared with the expression of the myelin basic protein (MBP). RNA was isolated from pooled human spinal cords obtained at three periods of development: 11-14 weeks, 17-19 weeks, and 21-23 weeks. Northern blot analysis revealed a 3.2-kilobase (kb) PLP mRNA that was present at higher abundance in the 21-23-week spinal cord RNA than in the 17-19-week or the 11-14-week samples. The 17-19-week RNA sample also contained a PLP-hybridizing band at 2.2 kb which may possibly have arisen by utilization of alternative polyadenylation signals. Messenger RNA for MBP was detectable at 11-14 weeks but was readily evident in both the 17-19- and 21-23-week age groups. Immunoblot analysis of whole spinal cord homogenates indicated that polypeptides for MBP preceded the appearance polypeptides for PLP by 3-4 weeks.

A new form of myelin basic protein found in human brain

Human myelin basic protein was subjected to ion-exchange chromatography at high pH to separate the differently charged components. Polyacrylamide gel electrophoretic patterns of the fractions showed that the less basic fractions 3, 4, and 5 contained significant amounts of a protein somewhat smaller than the more common 18.5-kDa form. Fraction 3 consisted of approximately equal amounts of this smaller polypeptide and component 3, the 18.5-kDa form found in other mammalian myelin basic protein preparations. The two proteins in fraction 3 were separated by fast protein liquid chromatography. Both have blocked N termini and identical C termini (-Met-Ala-Arg-Arg). When the tryptic digests of the two proteins were fractionated by HPLC, the elution profiles were similar, except that four peaks found in the chromatogram of the larger protein were missing from the chromatogram of the smaller one. In addition, an extra peak was found in the elution pattern of the latter chromatogram. Amino acid analysis of the individual tryptic peptides indicated that the smaller protein lacked residues 106-116 (-Gly-Arg-Gly-Leu-Ser-Leu-Ser-Arg-Phe-Ser-Trp-). The deleted portion corresponds exactly to the amino acid sequence encoded by exon 5 of the mouse basic protein gene. This new form of myelin basic protein has a molecular weight of 17,200, calculated from its amino acid composition.