Note: Double-layered polyimide film heater with low magnetic field generation

We designed a double-layered polyimide film heater where the direction of the injection current of each layer is opposite to that of the other layer to reduce the magnetic field. The width of the heater is 0.125 mm and the resistance is 21.2 Ω. This specially designed heater successfully demonstrated temperature controllability within 10 mK for an atomic cell in an atom spin gyroscope while minimizing the generation of the magnetic field to within 1 nT.

The effects of apigenin-7-O-beta-D-glucuronopyranoside on reflux oesophagitis and gastritis in rats

1. This study evaluated the inhibitory action of apigenin-7-O-beta-D-glucuronopyranoside (AGC), apigenin, and omeprazole on reflux oesophagitis and gastritis in rats. AGC was isolated from Clerodendron trichotomum leaves. 2. Oesophagitis and gastritis were induced by surgical procedure and the administration of indomethacin, respectively. The intraduodenal (i.d.) administration of AGC decreased the volume of gastric juice and increased the gastric pH compared with apigenin and omeprazole. The acid output was more inhibited by AGC in a dose-dependent manner than by apigenin and omeprazole. Compared with apigenin and omeprazole, AGC significantly decreased the size of gastric lesions, which were induced by exposure of the gastric mucosa to indomethacin. 3. Malondialdehyde (MDA) content, which is the end product of lipid peroxidation, was increased significantly after the induction of reflux oesophagitis. The MDA content was decreased by AGC (i.d. 3 mg kg(-1)), but not by either apigenin or omeprazole. This suggests that AGC has an antioxidative effect. In the oesophagitis group, the mucosal levels of glutathione (GSH) were significantly lower than that in the normal group. However, the GSH levels were preserved after administering the AGC, suggesting that AGC possesses scavenging activity. 4. In summary, AGC is more potent than apigenin and omeprazole at inhibiting reflux oesophagitis and gastritis and may therefore be a promising drug for their treatment.

Bioinformatics approaches for cross-species liver cancer analysis based on microarray gene expression profiling

Background

The completion of the sequencing of human, mouse and rat genomes and knowledge of cross-species gene homologies enables studies of differential gene expression in animal models. These types of studies have the potential to greatly enhance our understanding of diseases such as liver cancer in humans. Genes co-expressed across multiple species are most likely to have conserved functions. We have used various bioinformatics approaches to examine microarray expression profiles from liver neoplasms that arise in albumin-SV40 transgenic rats to elucidate genes, chromosome aberrations and pathways that might be associated with human liver cancer.

Results

In this study, we first identified 2223 differentially expressed genes by comparing gene expression profiles for two control, two adenoma and two carcinoma samples using an F-test. These genes were subsequently mapped to the rat chromosomes using a novel visualization tool, the Chromosome Plot. Using the same plot, we further mapped the significant genes to orthologous chromosomal locations in human and mouse. Many genes expressed in rat 1q that are amplified in rat liver cancer map to the human chromosomes 10, 11 and 19 and to the mouse chromosomes 7, 17 and 19, which have been implicated in studies of human and mouse liver cancer. Using Comparative Genomics Microarray Analysis (CGMA), we identified regions of potential aberrations in human. Lastly, a pathway analysis was conducted to predict altered human pathways based on statistical analysis and extrapolation from the rat data. All of the identified pathways have been known to be important in the etiology of human liver cancer, including cell cycle control, cell growth and differentiation, apoptosis, transcriptional regulation, and protein metabolism.

Conclusion

The study demonstrates that the hepatic gene expression profiles from the albumin-SV40 transgenic rat model revealed genes, pathways and chromosome alterations consistent with experimental and clinical research in human liver cancer. The bioinformatics tools presented in this paper are essential for cross species extrapolation and mapping of microarray data, its analysis and interpretation.

Long-term neuropsychological effects and MRI findings in patients with CS2 poisoning

OBJECTIVES

To evaluate the long-term neuropsychological effects and magnetic resonance imaging (MRI) findings among retired patients with a history of exposure to carbon disulfide (CS2).

MATERIAL AND METHODS

Seventy-four patients with a history of exposure to CS2 were divided into two equal groups according to their level of exposure, and they completed a questionnaire and were evaluated for neuropsychological symptoms using the Korean version of the revised Wechsler Adult Intelligence Scale. Thirty-one MRI images were reviewed retrospectively.

RESULTS

There were no statistically significant differences in total, verbal and performance IQs between high- and low-exposure groups. MRI findings revealed a significantly larger number of cerebral lacunae (five of 12 subjects) in the high-exposure group. Periventricular hyperintensities were mostly located in frontal and occipital areas, and white-matter hyperintensities were mostly in frontal and parietal areas.

CONCLUSION

The higher prevalence of lacunae in the high-exposure group as revealed by MRI suggests that further MRI studies are needed into long-term neuropsychological effects induced by CS2.

Bacterial mutagenicity of some tobacco aromatic nitrogen bases and their mixtures

The first aim was to compare the genotoxicities of two tobacco-specific nitrosamines (TSNA), 4-(methylnitrosamino)-(3-pyridyl)-1-butanone (NNK) and N'-nitrosonornicotine (NNN) in two types of tests, the Salmonella reverse mutation assay (250-2000 microg per plate) and the Mutatox test (up to 1000 microg/ml) using dark mutant M-169 of Vibrio fischeri. The second aim was to assess the effects of single other tobacco chemicals and metabolites (nicotine (NIC), cotinine (COT), trans-3-hydroxycotinine (3HC), cotinine-N-oxide (CNO) and nicotine-N-oxide (NNO)) on the mutagenic responses at relative concentrations observed physiologically. The Salmonella strains were TA100, TA7004, TA7005, and TA7006, all showing missense backmutations that are characteristic of the TSNA. NNN was a direct mutagen to strains TA100, TA7004, and in the Mutatox test, and was not mutagenic in the presence of rat or hamster S9. NNK was mutagenic only in strain TA7004 with rat and hamster S9, but not in TA100, but was directly mutagenic in the Mutatox test. While all the other tobacco chemicals were not mutagenic alone to strains TA100 and TA7004 in the presence and absence of rat or hamster S9, the Mutatox test produced direct mutagenicity for COT, 3HC, and NNO, but not CNO. The latter was mutagenic in the Mutatox test with rat or hamster S9, but only rat S9 was effective for COT, NNO and 3HC. Inhibitory potentiations of NNN by NIC and COT were observed on strain TA7004, and by NIC on strain TA100. There were no interactions on NNK in the presence of S9 for strain TA7004 or TA100. In contrast, a complex inhibition and enhancement behavior occurred in the Mutatox test for each interaction, but no effects were observed for CNO on NNK without S9, and few for NIC on NNK with hamster S9. Compounds which showed no activity alone modulated the genotoxicity of two potent TSNAs in both types of tests.

Differences in signal transduction pathways by which platelet-derived and fibroblast growth factors activate extracellular signal-regulated kinase in differentiating oligodendrocytes

Treatment of cultured rat oligodendroglial progenitors with either platelet-derived growth factor (PDGF) or fibroblast growth factor-2 (FGF-2) activated extracellular signal regulated kinase 2 (ERK2). Activation was transient in response to PDGF, whereas it was greater and more prolonged in response to FGF-2. ERK2 activation by PDGF was preceded by a very rapid, robust and transient tyrosine phosphorylation of the PDGF receptor. Although there was consistently more activation of ERK2 in response to FGF-2 than to PDGF, immunostaining of FGF receptors 1 (FGFR1) and 2 (FGFR2) and their tyrosine phosphorylation in progenitors was very weak, and both receptors were up-regulated during differentiation to oligodendrocytes. Tyrosine phosphorylation of the FGF receptors was maximal from 15 to 60 min of treatment and was sustained for many hours. Binding of radioiodinated FGF-2 to FGFR1 was predominant in progenitors, whereas binding to FGFR2 was predominant in oligodendrocytes. ERK2 activation by PDGF was more sensitive to inhibition of tyrosine kinases, whereas ERK2 activation by FGF-2 was relatively more sensitive to inhibitors of protein kinase C. These differences in signal transduction pathways probably contribute to the different cellular responses of oligodendroglial lineage cells to PDGF and FGF-2, respectively.

Conditional disruption of the aryl hydrocarbon receptor nuclear translocator (Arnt) gene leads to loss of target gene induction by the aryl hydrocarbon receptor and hypoxia-inducible factor 1alpha

To determine the function of the aryl hydrocarbon receptor nuclear translocator (ARNT), a conditional gene knockout mouse was made using the Cre-loxP system. Exon 6, encoding the conserved basic-helix-loop-helix domain of the protein, was flanked by loxP sites and introduced into the Arnt gene by standard gene disruption techniques using embryonic stem cells. Mice homozygous for the floxed allele were viable and had no readily observable phenotype. The Mx1-Cre transgene, in which Cre is under control of the interferon-gamma promoter, was introduced into the Arnt-floxed mouse line. Treatment with polyinosinic-polycytidylic acid to induce expression of Cre resulted in complete disruption of the Arnt gene and loss of ARNT messenger RNA (mRNA) expression in liver. To determine the role of ARNT in gene control in the intact animal mouse liver, expression of target genes under control of an ARNT dimerization partner, the aryl hydrocarbon receptor (AHR), was monitored. Induction of CYP1A1, CYP1A2, and UGT1*06 mRNAs by the AHR ligand 2,3,7,8-tetrachlorodibenzo-p-dioxin was absent in livers of Arnt-floxed/Mx1-Cre mice treated with polyinosinic-polycytidylic. These data demonstrate that ARNT is required for AHR function in the intact animal. Partial deletion of the Arnt allele was found in kidney, heart, intestine, and lung. Despite more than 80% loss of the ARNT expression in lung, maximal induction of CYP1A1 was found, indicating that the expression level of ARNT is not limiting to AHR signaling. Cobalt chloride induction of the glucose transporter-1 and heme oxygenase-1 mRNAs was also markedly abrogated in mice lacking ARNT expression, suggesting an inhibition of HIF-1alpha activity. These studies establish a critical role for ARNT in AHR and HIF-1alpha signal transduction in the intact mouse.

Translational suppression by hammerhead ribozymes and inactive variants in S. cerevisiae

The activity of hammerhead ribozymes in S. cerevisiae was assessed using two ribozymes that were designed to intramolecularly attack the hepatitis B viral X mRNA. The ribozymes effectively suppressed the expression of the X-lacZ fusion gene, when they were inserted at the 5' end of the X mRNA. The ribozymes cleaved the target RNA efficiently at the targeted phosphodiester bond, but the inactive mutants carrying G5-to-A substitution in the core did not, as the total RNA preparations of yeast extracts was assayed by primer extension. These G5A mutants, however, exerted the suppression as effectively as the wild-type ribozymes. The results, with several mutations introduced to a ribozyme, suggested that either mere formation of hammerhead-like structures with the three stems, or the formation of any two stems, could inhibit translation. Thus, the hammerhead-like structures, leading to cleavage or not, could effectively suppress translation, especially when formed around the initiation codon. The G5-to-A and U7-to-G mutations and replacement of the stem-II hairpin tetraloop did not appear to affect the formation of the inhibitory structure(s). The inhibition that was observed when stems I and III were directly connected without a loop or with a stem II hairpin was completely relieved when they were connected with only the loop of stem II (not containing the stem portion).

Genotoxicity of nicotine and cotinine in the bacterial luminescence test

Cotinine was positive in the absence of S9 in the bacterial luminescence genotoxicity test at 1.25 mg/ml (9-15 h incubation) and at 2.50 mg/ml (18-30 incubation hours) signifying potential mutagenicity and teratogenicity. In the presence of S9, cotinine was positive at 1.25 mg/ml after 9 incubation hours. In contrast, nicotine was not at any concentration or incubation time. Nicotine/cotinine mixtures were still positive at physiological concentrations, with potentiation relative to cotinine alone with and without S9. Standard additions of nicotine to other positive controls such as 2-aminoanthracene (2AA) (a mutagen causing point mutations on activation), phenol (a DNA intercalator), and N-methyl-N'-nitrosoguanidine (MNNG) (a direct-acting point mutagen) revealed a complex nicotine effect. Nicotine antagonized MNNG without S9, and potentiated MNNG with S9, 2AA with and without S9, and phenol without S9. Cotinine was not a very potent agent relative to the positive controls. Since cotinine has been considered an inactive biological monitoring marker of nicotine absorption in humans, the present results indicate that the many health effect correlations based on cotinine in urine, serum, saliva, and blood may involve more cause and effect than thought hitherto.

Comparison of the phosphorylation of myelin-associated glycoprotein in cultured oligodendrocytes and Schwann cells

Phosphorylation of the large and small isoforms of myelin-associated glycoprotein (L- and S-MAG) was investigated in primary oligodendrocyte cultures and in immortalized Schwann cells by incubating the cells with inorganic [32P]phosphate and immunoprecipitating MAG. In oligodendrocytes, both L- and S-MAG were phosphorylated, but L-MAG was much more heavily labeled. In Schwann cells, most of the phosphorylation was in S-MAG, which is the predominant isoform expressed by these cells. In both types of cells, the principal phosphorylated amino acid in MAG was serine. Radioactive phosphothreonine and phosphotyrosine were also detected in the MAG from oligodendrocytes. In Schwann cells, there was less phosphorylation of threonine and labeled phosphotyrosine was not detected. In both oligodendrocytes and Schwann cells, the phosphorylation of MAG was stimulated by phorbol ester and a calcium ionophore, but not by forskolin. The results indicate that the phosphorylation of MAG is catalyzed by protein kinase C and possibly other calcium-activated kinases in both types of myelinating cells, but not by cAMP-activated kinase. An inhibitor of tyrosine phosphatase, ammonium vanadate, increased the amount of radioactive phosphate in MAG several fold in both oligodendrocytes and Schwann cells. However, even in the presence of vanadate, the great majority of radioactivity in MAG was in phosphoserine and only a small amount was in phosphotyrosine, suggesting that tyrosine phosphorylation of other proteins may indirectly increase the phosphorylation of MAG. The current status of our understanding of MAG phosphorylation is reviewed in the context of similarities and differences between our results and other reports in the literature.

Expression of glycolipids and myelin-associated glycoprotein during the differentiation of oligodendrocytes: comparison of the CG-4 glial cell line to primary cultures

The expression of cerebrosides, sulfatides, gangliosides and the myelin-associated glycoprotein (MAG) during differentiation of the CG-4 line of oligodendrocyte progenitors [Louis et al.: J. Neurosci Res 31: 193, 1992] was compared with their expression in primary cultures of oligodendrocyte precursors [McCarthy and de Vellis: J Cell Biol 85: 890, 1980]. When the CG-4 cells differentiated from bipolar progenitors to oligodendrocytes, there was a decrease of glucosylcerebroside synthesis and an increase in galactosylcerebroside and sulfatide synthesis. However, even after differentiation, the incorporation of [3H]galactose into these glycolipids, the amounts of galactosylcerebroside and sulfatide, and the galactocerebroside/sulfatide ratio were all much less than in primary cultures of differentiating oligodendrocytes. The major gangliosides in differentiated primary oligodendrocyte cultures were GM3 and GD3, and GD3 was also a major ganglioside in the CG-4 line. However, unlike primary cultures of O-2A lineage cells in which GM3 synthesis increased dramatically during differentiation to oligodendrocytes, the CG-4 cells expressed very little GM3. Also, the CG-4 cells expressed larger amounts of more complex gangliosides, e.g. GD1b and GT1b, which were almost entirely restricted to the b-series. The amount of MAG expressed by the CG-4 cells increased substantially when they differentiated to oligodendrocytes, and it was almost all the large immature isoform. However, even after differentiation, the amount expressed was less than in differentiated primary oligodendrocyte cultures. Overall, the lower expression of myelin-related glycolipids and MAG by the CG-4 line suggests a lesser degree of differentiation in comparison to primary oligodendrocytes under the culture conditions of these experiments, but the larger amounts of cells available from the CG-4 line should be useful for investigating glycolipid and MAG function related to the early stages of myelinogenesis.

Differentiation of oligodendrocytes cultured from developing rat brain is enhanced by exogenous GM3 ganglioside

Cultures consisting primarily of O-2A progenitor cells and immature oligodendrocytes with a few microglia and astrocytes were obtained by shaking primary cultures from neonatal rat brain after 12-14 days in vitro. Addition of 50 micrograms/ml exogenous Neu-NAc alpha 2-3Gal beta 1-4Glc beta 1-1'ceramide (GM3 ganglioside) to the cultures resulted in an increase in the number and thickness of cell processes that stained intensely for sulfatide and galactocerebroside (galC) in comparison to control cultures without added GM3. The treated cultures also contained fewer astrocytes than control cultures as revealed by immunostaining for glial fibrillary acidic protein (GFAP). Cells that immunostained for both GFAP and sulfatide/galC were very rare in control cultures but were frequently seen in the GM3-treated cultures, suggesting that these may represent cells changing their direction of differentiation away from type II astrocytes toward oligodendrocytes under the influence of GM3. These effects on the developing rat oligodendrocytes were specific for GM3 ganglioside and were not produced by adding GM1, GM2, GD3, or GD1a to the cultures. Lactosyl ceramide and neuraminyl lactose were also ineffective. When control cultures were initially plated on polylysine and incubated with [14C]galactose, GD3 was the principal labeled ganglioside. However, as the control cells differentiated over time in culture without the addition of exogenous GM3 and produced increasing amounts of myelin-related components, the incorporation of [14C]galactose into endogenous GM3 increased to become the predominant labeled ganglioside by 6 days after plating. Metabolic labeling of the GM3-treated oligodendrocytes with [14C]galactose revealed increased incorporation into galC and sulfatide in comparison to control cultures, but a decreased labeling of endogenous GM3. Similarly, incorporation of an amino acid precursor into the myelin-associated glycoprotein (MAG) was increased by GM3 treatment, but incorporation into myelin basic protein (MBP) was not affected. Although the overall effect of added GM3 was to decrease the phosphorylation of most proteins in the oligodendrocytes, including MBP, GM3 enhanced the phosphorylation of MAG. These findings indicate that GM3 ganglioside has an important role in the differentiation of cells of the O-2A lineage toward myelin production, since differentiation is associated with increased metabolic labeling of endogenous GM3 in control cultures and is enhanced by the addition of exogenous GM3.

Oligodendrocyte proteoglycans: modulation by cell-substratum adhesion

The signals that trigger the cytodifferentiation of oligodendrocytes (OLGs) are largely unknown. Using as a model system cultures of pure OLGs, we have shown that adhesion to a substratum initiates myelinogenesis (Yim SH, Szuchet S, Polak PE, J Biol Chem 261:11808-11815, 1986). It was of interest to investigate whether components such as proteoglycans (PGs) play any role in the biology of OLGs as it pertains to myelinogenesis. We set out to determine first, whether OLGs carry PGs; second, the nature of the association of these components with OLG plasma membrane; and third, if and how these PGs are modulated by OLG-substratum interaction. We compared the expression and characteristics of PGs extracted with different solvents from nonattached (B3.f) and attached (B3.fA) OLGs. B3.f and B3.fA OLG cultures were labeled with carrier-free 35SO4(2-) in serum-free medium. After removing excess label, OLGs were treated with heparin to extract susceptible components. Pellets were then exposed to 1% Triton X-100 plus 0.1 M NaCl and subsequently to 4 M guanidine-HCl plus 0.5 M NaCl. Solutions containing extracted material were characterized by size-exclusion chromatography, SDS-PAGE, and enzymatic degradation. Herein we report that (1) OLGs display [35S]PGs on their surface within 24 hr of substratum adhesion, and (2) these PGs can be operationally classified as peripheral and integral. We further show that the peripheral PGs are of high and intermediate size as assessed by size-exclusion chromatography and are segregated within the plasma membrane in such a way that the species with intermediate mass are extracted while OLGs remain adhered, whereas the high-molecular-weight species are only extracted after OLGs have been detached. Heparin also dislodges a number of sulfated proteins/Gps. Only a single class--high molecular weight--of integral PGs was identified; this PG requires guanidine-HCl for extraction. All PGs belong to the heparan sulfate class as evidenced by their degradation with heparitinase and their lack of susceptibility to chondroitinase ABC. The common theme of our findings is that these macromolecules have basal levels of expression in the nonadhered OLGs but undergo an adhesion-induced enhancement in their syntheses. We postulate that these PGs (1) play a role in OLG-substratum adhesion and hence myelinogenesis, and (2) may be determinants in establishing OLG polarity. Such polarization is the first overt sign of OLG functional differentiation and occurs prior to any morphological differentiation, e.g., extension of processes does not occur until 48 hr later when the plasma membrane is already polarized.

Biosynthesis and expression of the myelin-associated glycoprotein in cultured oligodendrocytes from adult bovine brain

The biosynthesis and expression of myelin-associated glycoprotein (MAG) were investigated in cultured oligodendrocytes isolated from adult bovine brain. Western blotting revealed two prominent MAG bands that were present in comparable amounts; the larger component electrophoresed above the 97 kD standard but was slightly smaller than the MAG band in purified bovine myelin, and the smaller component electrophoresed below the 97 kD standard. In comparison to other precursors of oligosaccharides, inorganic [35S]sulfate was a relatively specific isotope for labeling MAG relative to other glycoproteins in the cells. Sulfate labeled only the larger of the two MAG components, which contains complex N-linked oligosaccharides, but which appears to be glycosylated to a lesser extent than MAG in vivo. The smaller MAG band in the cells is a form with high-mannose oligosaccharides and was not detected in purified bovine myelin. Both the large and small MAG components were expressed on the oligodendrocyte surface as indicated by their sensitivity to neuraminidase and/or trypsin treatment of live cells. MAG was also released by the oligodendrocytes into the culture medium. The MAG in the medium was slightly smaller than that in the cells, suggesting that it may be released from the cell surface by limited proteolysis. The release of MAG by myelin-forming cells could be relevant to physiological roles that have been postulated for soluble forms of MAG and other adhesion proteins.

Exogenous GM3 ganglioside stimulates process formation and glycoprotein release by cultured bovine oligodendrocytes

Isolated adult bovine oligodendrocytes maintained in vitro for 10 days were treated for 1 day with 50 micrograms/ml of GM3 ganglioside (NeuNac alpha 2-3Gal beta 1-4Glc beta 1-1'ceramide) in serum-free culture medium. The treated oligodendrocytes had significantly longer processes with more branching than control cells in the same medium without GM3. The treatment also stimulated the release of a series of 22-100-kDa, [3H]glucosamine-labeled glycoproteins into the culture medium. Treatment of oligodendrocytes maintained in vitro for 50 days with GM3 for 1 day resulted in a thickening of the processes and the appearance of many fine branches on existing processes as well as a similar stimulation of glycoprotein release into the medium.

Plasma membrane of cultured oligodendrocytes: II. Possible structural and functional domains

An oligodendrocyte plasma membrane-rich fraction, F2.2, was resolved by equilibrium density centrifugation on a linear sucrose gradient from 0.5 M to 1.3 M into three fractions, F2.2a, F.2.2b, F2.2c, and a pellet F2.2p. F2.2a and F.2.2b were enriched 1.5-fold relative to F2.2 in plasma membrane markers at the expense of F2.2c and F2.2p, which became correspondingly impoverished. This gave F2.2a and F2.2b a 42-fold and 37-fold enrichment, respectively, in plasma membrane markers relative to the initial cell homogenate. F2.2c had a sevenfold enrichment in a Golgi marker; together with F2.2p, they contained all the Golgi marker initially present in F2.2. Preliminary data indicated that the F2.2-subfractions differed from one another in their molar ratios of cholesterol to phospholipids and protein to lipids but had similar protein profiles when examined by sodium dodecylsulfate-polyacrylamide gel electrophoresis. Their content of fucosylated glycoproteins appeared also to be different. Morphologically, F2.2a and F2.2b were very similar: they contained large membrane vesicles, membrane sheets, and vesicles entrapped within other vesicles. Membrane-membrane interaction was apparent in these fractions. F2.2c had many of the same elements, but most of the membrane structures contained amorphous material. F2.2p differed morphologically from the other fractions in that it had principally electron-dense structures. It is postulated that F2.2a, F2.2b, and perhaps F2.2c represent different domains of oligodendrocyte plasma membrane. Alternatively, these fractions might correspond to the plasma membrane of oligodendrocyte subtypes.

Plasma membrane of cultured oligodendrocytes: III. Relatedness to myelin

We have compared highly purified fractions of oligodendrocyte plasma membrane to myelin by one- and two dimensional gel electrophoresis and found them to be distinct. The major myelin proteins--proteolipid protein (PLP), DM-20, and myelin basic protein (MBP), which dominate the sodium dodecyl sulfate polyacrylamide gel electrophoresis pattern of myelin--were minor components of the plasmalemma. However, 2',3', cyclic nucleotide phosphodiesterase (CNPase) and myelin-associated glycoprotein (MAG) were represented equally in both membranes. Labeling the cells with various precursors followed by isolation of plasmalemma revealed that newly synthesized PLP, DM-20, CNPase, and MAG were incorporated into the plasma membrane of "floating" oligodendrocytes (i.e., nonattached to substratum). This was not so with MBP. Nevertheless, scattered patches of MBP were localized on the plasma membrane of intact cells using the immunogold method at the electron microscopic level. The data are consistent with the notion that MBP is not a constituent of the plasma membrane of mature oligodendrocytes (the MBP patches on intact cells are likely remnants from past association with myelin) but is rapidly associated with the plasmalemma of myelinating oligodendrocytes (i.e., attached cells). It is suggested that phosphorylation of MBP provides the triggering signal for plasma membrane association. In order to analyze the minor proteins in myelin and compare them to the plasma membrane by two-dimensional gel electrophoresis, myelin was extracted with chloroform:methanol to remove PLP, DM-20, and MBP. Even in the absence of PLP, DM-20, and MBP the pattern of extracted myelin still differed from that of plasmalemma indicating that their minor protein compositions were not the same. Myelin was characterized by a group of proteins that clustered at pI 5.5-6.5 and Mr 40,000-60,000 of which alpha-tubulins, beta-tubulins, and actin are part: the plasmalemma had tubulins and actin but in different proportions. Our findings indicate that in addition to PLP, DM-20, and MPB, myelin is also enriched relative to the plasmalemma in another group of proteins.

Cultured oligodendrocytes. A role for cell-substratum interaction in phenotypic expression

Oligodendrocytes can be maintained in two states: nonattached; we call these cells B3.f; morphologically they resemble freshly isolated cells; attached; we refer to the latter as B3.fA. Profound morphological, ultrastructural, and biochemical changes take place upon adhesion to a competent surface (Szuchet, S., Yim, S. H., and Monsma, S. (1983) Proc. Natl. Acad. Sci. U. S. A. 80, 7019-7023). Here we present evidence that the transition from B3.f to B3.fA has important consequences for the expression of myelinogenic properties by these cells. We have examined the incorporation of [3H]leucine, [35S]methionine, and [35S]cysteine into polypeptide chains by B3.f and B3.fA cells from 3 days after isolation up to 8 weeks in culture. Specific antisera against myelin and cytoskeletal proteins were used to identify the newly synthesized proteins. Our results indicate that: overall incorporation expressed as cpm/mg of protein remains essentially constant and independent of the state of adhesion or time in culture; B3.f cells keep a low profile in the synthesis of the major myelin proteins but have a high uptake of precursors into 2',3'-cyclic nucleotide phosphodiesterase, actin, and tubulin; adhesion of oligodendrocytes to a polylysine substratum activates the synthesis and phosphorylation of myelin basic protein, and the synthesis and acylation of proteolipid protein and DM-20; over time in culture there is an increased synthesis and accumulation of these proteins and of myelin-associated glycoprotein. We conclude that B3.f cells exhibit a behavior that is distinct from that of B3.fA cells. Our results are consistent with the notion that upon adhesion to a substratum, oligodendrocytes undergo a transition from myelin-maintaining cells (B3.f) to that of myelin-forming cells (B3.fA). This conclusion is substantiated by the finding of myelin membranes in these cultures.

Mature oligodendrocytes cultured in the absence of neurons recapitulate the ontogenic development of myelin membranes

We have maintained isolated oligodendrocytes in culture for up to 5 months. Over time cultured cells acquire conspicuous membranous profiles that either emanate from cell processes and perikarya or are apposed to them. These membranous profiles have biochemical and ultrastructural features characteristic of myelin. Because the cells used in this study are post-myelination (cells are isolated from white matter of mature brains), we argue that this is a case of resynthesis of myelin membranes. Because this process takes place in the absence of neurons, we have termed it myelin palingenesis in order to distinguish it from remyelination, a term commonly used to designate reensheathment of axons. Myelin palingenesis may occur seemingly without wrapping and spiraling, but membranes wrapped around oligodendrocyte processes and soma are also observed. Irrespective of the modes of formation, those membranes that are compact have the fine structure of normal myelin. Thus, long-term cultures of mature oligodendrocytes should be a good model system in helping to decipher the molecular and cellular mechanisms involved in myelination and in remyelination.

Lipid and glycolipid metabolism of cultured astrocytes: a time course study

Primary cultures of astrocytes free of neurons and containing less than 1% of oligodendrocytes were examined for their ability to incorporate labeled precursors into lipids and glycolipids. At selected developmental stages cultures were double-labeled with either [3H]glycerol and [14C]acetate or with [3H]galactose and Na2[35SO4] for a total of 72 hr. Lipids were extracted with CHCl3/CH3OH, fractionated on a silicic acid column, and further resolved by two-dimensional thin-layer chromatography. It was found that cultured astrocytes actively incorporate acetate and glycerol into various phospholipids; they have very limited ability to utilize galactose and virtually lack the synthetic machinery to use Na2SO4 for the synthesis of sulfated sphingogalactolipids; and their overall lipid metabolism is very distinct from that of oligodendrocytes. It was also found that cultured astrocytes have low levels of 2',3' cyclic phosphodiesterase and glycerol phosphate dehydrogenase activities; the latter is less than one fifth of that in oligodendrocytes.

A monoclonal antibody that binds to both astrocytes and myelin sheaths

A monoclonal antibody designated III 5H8 was shown to bind both to astrocytes and to myelin sheaths as studied with immunocytochemical techniques on brain sections and cell cultures. Binding to astrocytes was confirmed by double immunofluorescent labelling of frozen sections and cell cultures with anti-GFAP, and appeared to be sensitive to formalin treatment. Binding to myelin sheaths was confirmed by comparing sections labelled with III 5H8 with sections labelled with antibodies against axons and myelin basic protein as well as by staining of sections of hypomyelinated spinal cord with III 5H8. On immunoblots of separated white matter III 5H8 revealed two bands, while on immunoblots of purified myelin only one band was seen. The findings are discussed with respect to the function of astrocytes in white matter and shared antigenic determinants between astrocytes and oligodendrocytes.

Characterization of a subset of oligodendrocytes separated on the basis of selective adherence properties

A subset of oligodendrocytes (B3,f) was isolated by taking advantage of selective cell-substratum interaction. B3,f cells were characterized morphologically, biochemically, and immunocytochemically. Oligodendrocytes were isolated from 4-to-6-month-old lamb brains by a modified version of our published procedure [Szuchet et al, J Neurosci Methods 3:7-19, 1980]. Freshly isolated cells from band III were plated on plastic culture plates at a concentration of 2 X 10(6) cells/ml. Approximately 40% of the cells attached to the plate under these conditions. The remaining cells formed small floating clusters. We refer to the latter as B3,f oligodendrocytes. After 4 to 5 days, the supernatant containing B3,f cells was removed and centrifuged, and the pellet was resuspended in culture medium and replated on polylysine-coated petri dishes. B3,f oligodendrocytes attached to this surface and extended an intricate network of processes. The purity of the cultures, judged by the number of cells staining with a monoclonal antibody against galactocerebroside was 98-99%. This high degree of cell homogeneity was maintained throughout the life of the cultures. B3,f cells appeared to be highly differentiated and remained so in vitro. This is surmised by the expression of oligodendrocytic characteristic functions such as high levels of CNPase activity typically, 5 microM/min/mgP; high incorporation of H2 35SO4 into sulfatides, an overall lipid metabolism that mimics events associated with myelinogenesis [Szuchet et al, PNAS 80:7019-7023, 1983]; the presence, detected immunocytochemically, of myelin-associated glycoprotein and myelin basic proteins. It is concluded that this culture system offers an opportunity for studying the biology of interfascicular oligodendrocytes and their interaction with neurons and/or astrocytes. It also should open up a way of examining the relevance of oligodendrocyte polymorphism.

Lipid metabolism of isolated oligodendrocytes maintained in long-term culture mimics events associated with myelinogenesis

Oligodendrocytes isolated from ovine white matter according to a published procedure [Szuchet, S., Stefansson, K., Wollmann, R. L., Dawson, G. & Arnason, B. G. W. (1980) Brain Res. 200, 151-164] were cultured for up to 35 days and their capacity to incorporate precursors into lipids was investigated. At various times, cultures were double labeled with [3H]glycerol/[14C]acetate or [3H]galactose/35SO2-4. The cells were harvested 72 hr later and lipids were fractionated using standard procedures. The time course of incorporation for each precursor was distinct. In the days after attachment to substratum, oligodendrocytes preferentially incorporated [3H]glycerol into phospholipids and [14C]acetate into cholesterol while uptake of 35SO2-4 and [3H]galactose into glycolipids was modest. A switch in phospholipid metabolism from preferential incorporation into phosphatidylcholine to incorporation into phosphatidylethanolamine, phosphatidylserine, and phosphatidylinositol occurred at about the 10th day in vitro. After 20 days, uptake of [3H]glycerol into phospholipids and [14C]acetate into cholesterol had stabilized but incorporation of 35SO2-4 into glycolipids had increased. 35SO2-4 incorporation into glycolipids was even greater at 35 than at 20 days. Uptake of [3H]galactose did not change over time. An attempt was made to correlate changes in lipid metabolism with morphologic developments. High incorporation into phospholipids and cholesterol coincided in time with the extensive membrane synthesis required for cell attachment and process extension. Differentiation of these newly formed membranes, as assessed by the incorporation of myelin-characteristic glycolipids, galactocerebrosides, and sulfatides, occurred at a time when an intricate network of processes had already been established. The sequence of metabolic events observed in vitro parallels that observed at the onset of myelinogenesis in vivo. We postulate that mature oligodendrocytes can reenact those early events associated with myelinogenesis.