Lethal adulthood myelin breakdown by oligodendrocyte-specific Ddx54 knockout

Multiple sclerosis (MS) is a leading disease that causes disability in young adults. We have previously shown that a DEAD-box RNA helicase Ddx54 binds to mRNA and protein isoforms of myelin basic protein (MBP) and that Ddx54 siRNA blocking abrogates oligodendrocyte migration and myelination. Herein, we show that MBP-driven Ddx54 knockout mice (Ddx54 fl/fl;MBP-Cre), after the completion of normal postnatal myelination, gradually develop abnormalities in behavioral profiles and learning ability, inner myelin sheath breakdown, loss of myelinated axons, apoptosis of oligodendrocytes, astrocyte and microglia activation, and they die within 7 months but show minimal peripheral immune cell infiltration. Myelin in Ddx54fl/fl;MBP-Cre is highly vulnerable to the neurotoxicant cuprizone and Ddx54 knockdown greatly impairs myelination in vitro. Ddx54 expression in oligodendrocyte-lineage cells decreased in corpus callosum of MS patients. Our results demonstrate that Ddx54 is indispensable for myelin homeostasis, and they provide a demyelinating disease model based on intrinsic disintegration of adult myelin.

The Absence of Myelin Basic Protein Reduces Non-Amyloidogenic Processing of Amyloid Precursor Protein

BACKGROUND

The accumulation of amyloid β-protein (Aβ) in the brain is a pathological feature of Alzheimer's disease (AD). Aβ peptides originate from amyloid precursor protein (APP). APP can be proteolytically cleaved through amyloidogenic or non-amyloidogenic pathways. The molecular effects on APP metabolism / processing may be influenced by myelin and the breakdown of myelin basic protein (MBP) in AD patients and mouse models of AD pathology.

METHODS

We directly tested whether MBP can alter influence APP processing in MBP-/- mice, known as Shiverer (shi/shi) mice, in which no functional MBP is produced due to gene breakage from the middle of MBP exon II.

RESULTS

A significant reduction of the cerebral sAPPα level in Shiverer (shi/shi) mice was found, although the levels of both total APP and sAPPβ remain unchanged. The reduction of sAPPα was considered to be due to the changes in the expression levels of a disintegrin and metalloproteinase-9 (ADAM9) catalysis and non-amyloid genic processing of APP in the absence of MBP because it binds to ADAM9. MBP -/- mice exhibited increased Aβ oligomer production.

CONCLUSION

Together, these findings suggest that in the absence of MBP, there is a marked reduction of non-amyloidogenic APP processing to sAPPα, and targeting myelin of oligodendrocytes may be a novel therapy for the prevention and treatment of AD.

Phase separation of myelin sheath in Triton X-114 solution: predominant localization of the 21.5-kDa isoform of myelin basic protein in the lipid raft-associated domain

Myelin basic protein (MBP) isoforms in the myelin sheath are known to have distinct intracellular expression patterns, which are profoundly related to functional specificity. Determining the differential localization of MBP isoforms is therefore important for understanding their pathophysiological roles. In this study, we have developed a new method for phase separation of myelin. The non-ionic detergent Triton X-114 is used to solubilize myelin sheath which then undergoes phase separation to yield four fractions. The lipid raft-associated proteins and lipids in each fraction were analysed by immunoblotting and lipid analysis, respectively. The present method gives two lipid raft-enriched fractions, one of them was found to contain only lipid raft-associated galactocerebroside and cholesterol as the major lipids. The 21.5-kDa MBP isoforms (21.5 MBP), both unphosphorylated and phosphorylated, were exclusively contained in this fraction. Phosphorylated 21.5 MBP (21.5 pMBP) has been shown to specifically disappear from demyelinated loci. The present analytical method clearly indicated that disappearance of 21.5 pMBP corresponded to demyelination and its reappearance corresponded to prevention of demyelination. Demyelination was also associated with aging and was prevented by the myelin-protecting herbal medicine, Chinpi, a type of dried citrus peel.

A DEAD-box RNA helicase Ddx54 protein in oligodendrocytes is indispensable for myelination in the central nervous system

We recently reported that a new monoclonal antibody, 4F2, which labels oligodendroglial lineage cells, recognizes a DEAD-box RNA helicase Ddx54 and that Ddx54 binds to myelin basic protein (MBP) in brain and cultured oligodendrocytes. To elucidate the biological function of Ddx54, we generated a recombinant adenovirus, Ad-shRNA:Ddx54, expressing a short hairpin RNA to silence endogenous Ddx54 protein. The virus was intraventricularly injected into the brains of mice on postnatal day (PD) 2. The brains at PD 9 were then analyzed by immunohistochemistry. In untreated normal brain sections, as well as control brains that had been injected with Ad-β-Gal, myelination of axons occurred in the corpus callosum with filamentous patterns of immunosignals of myelin-associated glycoprotein (MAG) and MBP. In Ad-shRNA:Ddx54-injected brain, substantial amounts of MAG and MBP immunosignals were present, but MBP immunosignals accumulated in the subplate layer and did not intrude into the emerging white matter. Immunoblot analysis revealed that Ddx54 knockdown caused a significant decrease in the level of 21.5 kDa MBP isoform and Ddx54, but the amount of Olig2; 2',3'-cyclic nucleotide 3' phosphodiesterase; MAG; three MBP isoforms (14, 17.5, and 18 kDa); and QKI-5, QKI-6, and QKI-7 proteins remained unchanged. Transfection of the Ddx54 expression vector into luciferase reporter-introduced neuroepithelial cells resulted in upregulated MBP promoter activity. Immunoprecipitation of Ddx54 protein in MBP-transfected HEK293 cells indicated that Ddx54 may directly interact with MBP mRNA. These results suggest that Ddx54 protein play an important role in central nervous system myelination, presumably in myelin sheath formation after the differentiation of oligodendrocytes.

A new monoclonal antibody, 4F2, specific for the oligodendroglial cell lineage, recognizes ATP-dependent RNA helicase Ddx54: possible association with myelin basic protein

Recent research in neural development has highlighted the importance of markers to discriminate phenotypic alterations of neural cells at various developmental stages. We isolated a new monoclonal antibody, 4F2, which was shown to be specific for an oligodendrocyte lineage. In primary cultures of oligodendroglial and mixed neural cells, the 4F2 antibody labeled a large proportion of Sox2(+) , Sox10(+) , A2B5(+) , NG2(+) , Olig2(+) , O4(+) , and myelin basic protein (MBP)(+) cells but did not label any GFAP(+) or NeuN(+) cells. In immunohistochemisty of rat embryos, the 4F2 antibody labeled a portion of neuroepithelial cells of the neural tube at embryonic day 9. The 4F2-positive cells were located initially in the ventricular zone as Musashi1(+) Tuj1(-) populations and distributed throughout the striatum; thereafter, they populated the whole brain and spinal cord. These cells showed ramified processes during embryonal development. The 4F2 antigen was associated with all four isoforms of MBP in coimmunoprecipitation experiments using brain homogenates or cell lysates of cultured oligodendrocytes. Immunoscreening of a brain cDNA library identified the antigen as DEAD (Asp-Glu-Ala-Asp) box polypeptide 54 (Ddx54), a member of the DEAD box family of RNA helicases involved in RNA metabolism, transcription, and translation. Cotransfection of the Ddx54 gene with MBP isoform genes increased the nuclear localization of the 21.5-kDa MBP isoform, which has been reported to function as a nuclear signal transduction molecule. These data indicate that Ddx54 might be not only a useful marker for investigating the ontogeny of oligodendrocytes but also an important factor in oligodendrocyte differentiation and myelination.

Administration of chinpi, a component of the herbal medicine ninjin-youei-to, reverses age-induced demyelination

The disruption of myelin causes severe neurological diseases. An understanding of the mechanism of myelination and remyelination is essential for the development of therapeutic strategies for demyelination diseases. Our previous findings indicated that the FcRγ/Fyn cascade is a potential therapeutic target for remyelination caused by the Chinese/Japanese traditional herbal (Kampo) medicine ninjin'youeito (Ninjin-youei-to, NYT), which is a hot-water extract made from 12 medicinal herbs. To identify which constituents of NYT are involved in the reversal of demyelination and to examine the potential therapeutic effect, we tested several of the chemical constituents of NYT. Here, we report that Chinpi, a constituent of NYT, upregulates the FcRγ/Fyn signaling cascade resulting in a potentially therapeutic effect against age-induced demyelination. In addition, we observed that phosphorylated (activated) FcRγ/Fyn upregulated the expression of the 21.5 kDa isoform of myelin basic protein, inducing rapid morphological differentiation, when oligodendrocyte precursor cells (OPCs) were cultured in the presence of hesperidin and/or narirutin (the major active constituents of Chinpi). These results suggest that hesperidin and narirutin participate in the FcRγ/Fyn signaling pathway in OPCs causing these cells to differentiate into myelinating oligodendrocytes.

Hypothermia-induced increase of oligodendrocyte precursor cells: Possible involvement of plasmalemmal voltage-dependent anion channel 1

Hypothermia is believed to suppress cell proliferation by inducing apoptosis/necrosis and phase-specific/nonspecific cell cycle arrest, which are, directly or indirectly, related to a reduced energy supply. Intriguingly, hypothermia is known to improve neurological recovery of animals and humans exposed to focal brain hypoxic-ischemic injury. The underlying mechanism of the neuroprotective effect of hypothermia is unclear, although the prevention of neural cell apoptosis is thought to play a role. Herein we demonstrate that in vitro cell culture of oligodendrocyte precursor cells (OPCs) under conditions of mild hypothermia (31.5°C) results in an increase in cell number relative to cells cultured under normothermic conditions (37°C). Cell cycle analysis, immunoblotting of cyclins, TUNEL assay, and immunocytochemistry of OPC differentiation markers suggest that hypothermia shifts the balance between proliferation and apoptosis/differentiation toward proliferation. A combination of transcriptome analysis, pharmacological intervention, and immunoaffinity-based assays suggests a possible involvement of the Gα13-Rho GTPase Cdc42-ERK1/2 signaling cascade and voltage-dependent anion channel 1 (VDAC1), which associate or dissociate with Gα13 protein at 37°C and 31.5°C, respectively. Immunoelectron microscopy revealed the presence of VDAC1 in the plasma membrane of OPCs. Furthermore, the exogenous addition of impermeable VDAC1 inhibitors enhanced proliferation of OPCs at 37°C. These results may contribute to the elucidation of the mechanism of hypothermic neuroprotection as well as the possible novel role of plasmalemmal VDAC1.

Restoration of FcRγ/Fyn signaling repairs central nervous system demyelination

Disruption of myelin causes severe neurological diseases. An understanding of the mechanisms that control myelination and remyelination is needed to develop therapeutic strategies for demyelinating diseases such as multiple sclerosis (MS). Our previous finding indicating the critical involvement of the gamma chain of immunogloblin Fc receptors (FcRgamma) and Fyn signaling in oligodendrocyte differentiaion and myelination demands a fundamental revision of the strategies used for MS therapy, because antigen-antibody complexes in MS patients may induce the direct dysregulation of myelination process as well as the inflammatory destruction of myelin sheath. Here we show that the FcRgamma/Fyn signaling cascade is critically involved in cuprizone-induced demyelination/remyelination, with no lymphocytic response. The levels of phosphorylated myelin basic proteins (p-MBPs), especially the 21.5-kDa isoform, but not the levels of total MBPs, decreased markedly during demyelination induced by aging, cuprizone treatment, and double knockout of FcRgamma/Fyn genes. We also showed that the recovery from demyelination in cuprizone-treated and aged mice is achieved after administration of the herbal medicine Ninjin'yoeito, an effective therapy targeting the FcRgamma/Fyn-Rho (Rac1)-MAPK (P38 MAPK)-p-MBPs signaling cascade. These results suggest that the restoration of FcRgamma/Fyn signaling represents a new approach for the treatment of demyelinating diseases.

Involvement of CD45 in central nervous system myelination

Myelin is a multi-layered membranous lipid insulator surrounding axons that allows the rapid conduction of neuronal impulses. In the central nervous system (CNS), myelin is produced by oligodendrocytes. During development, morphologically immature oligodendrocyte precursor cells (OPCs) arise from neural stem cells before differentiating into myelinating oligodendrocytes shortly after birth. Fyn tyrosine kinase (Fyn) has been shown to play a central role during OPC differentiation, including inducing morphological changes in the cells and initiating the expression of myelin basic protein (MBP), a major structural protein required for the compaction of myelin sheaths. Recently, we have shown that signaling via the gamma chain of immunoglobulin Fc receptors (FcRgamma) induces the Fyn-MBP cascade and promotes the morphological differentiation of OPCs. The protein tyrosine phosphatases that are responsible for the positive regulation of Fyn tyrosine kinase activity during this cascade, however, remained unknown. Here we report that a protein tyrosine phosphatase, CD45, is involved in this process. Fyn co-immunoprecipitated with CD45 from differentiating wild-type OPCs in vitro, while CD45-deficient OPCs failed to differentiate. Additionally, dysmyelination was observed in CD45-deficient mice in vivo. Our findings suggest that CD45 is a key phosphatase involved in OPC differentiation and provide a preliminary explanation for the previously reported CD45 mutations observed in some multiple sclerosis (MS) patients.

Myelination triggers local loss of axonal CNR/protocadherinα family protein expression

The cadherin-related neuronal receptor (CNR)/protocadherin (Pcdh) alpha family is one of the diverse protocadherin families expressed in developing axons. We observed a strong axonal expression of these proteins at late embryonic and early postnatal stages corresponding to regions where fibers had not yet been myelinated. We therefore followed the postnatal localization of CNR/Pcdh alpha protein in major axonal tracts, such as the internal capsule, lateral olfactory tract, and optic nerve, and found that its axonal localization was dramatically lost in parallel with the increased expression of myelin markers. Moreover, the hypomyelinated optic nerve tracts of the myelin-deficient Shiverer mouse exhibited elevated levels of CNR/Pcdh alpha expression. These axonal expression patterns of CNR/Pcdh alpha in wild-type and Shiverer mice were similar to those of growth associated protein 43 (GAP-43) and L1, both of which are associated with axonal maturation. Thus, myelination may be a trigger for the local loss of axonal CNR/Pcdh alpha protein, and this process may be important in the maturation of neural circuits.

Bisphenol A exerts thyroid-hormone-like effects on mouse oligodendrocyte precursor cells

We report studies on the mechanism of action of bisphenol A (BPA) on the differentiation of oligodendrocyte precursor cells (OPCs). Our results show that: (1) BPA inhibits the differentiation of OPCs induced by exposure to thyroid hormone (T3). (2) The effect is mediated through various mechanisms via the thyroid hormone receptor (TRbeta1) which is considered to be responsible for OPC differentiation. (3) The action of BPA on OPC differentiation does not involve the FcRgamma-Fyn-myelin basic protein (MBP) cascade as an inducer of OPC differentiation nor does it suppress CREB phosphorylation, which is considered to be induced by the T3-TR complex. (4) The presence of MBP isoforms (21.5, 18.5, 17.0 and 14.0 kDa) was detected in OPCs, and the expression of exon 2-containing isoforms (i.e. 17.0 and 21.5 kDa) was upregulated upon treatment with T3. In contrast, expression of MBP was inhibited by BPA.

Effect of a traditional Chinese herbal medicine, Ren-Shen-Yang-Rong-Tang (Japanese name: Ninjin-Youei-To), on oligodendrocyte precursor cells from aged-rat brain

Understanding of oligodendrocyte precursor cells and their role in the generation of oligodendrocytes in developing and adult rodents has been considered, particularly much less is known about aged-rodent oligodendrocyte precursor cells and their cell lineage. In this present study, we have developed oligodendrocyte cultures from the 30-month-old rat brain and examined whether oligodendrocyte precursor cells can proliferate in vitro. Adult oligodendrocyte precursor cells (O1(-), O4(+)) and oligodendrocytes (O1(+), O4(+)) are present in the cultures of the 30-month-old rat brain. They are also capable of proliferating and differentiating in the cultures. These capabilities increased four- to fivefold, when the aged rats are treated with Ninjin-Youei-To for 3 months in comparison with those of control aged rats. These results suggest that Ninjin-Youei-To has a potential mitotic effect on oligodendrocyte precursor cells in aged-rat brains and may be expected to have a therapeutic effect on brain aging.

Signaling via immunoglobulin Fc receptors induces oligodendrocyte precursor cell differentiation

Dramatic changes in morphology and myelin protein expression take place during the differentiation of oligodendrocyte precursor cells (OPCs) into myelinating oligodendrocytes. Fyn tyrosine kinase was reported to play a central role in the differentiation process. Molecules that could induce Fyn signaling have not been studied. Such molecules are promising therapeutic targets in demyelinating diseases. We provide evidence that the common gamma chain of immunoglobulin Fc receptors (FcRgamma) is expressed in OPCs and has a role in triggering Fyn signaling. FcRgamma cross-linking by immunoglobulin G on OPCs promotes the activation of Fyn signaling and induces rapid morphological differentiation with upregulation of myelin basic protein (MBP) expression levels. Mice deficient in FcRgamma are hypomyelinated, and a significant reduction in MBP content is evident. Our findings indicate that the FcRgamma-Fyn-MBP cascade is pivotal during the differentiation of OPCs into myelinating oligodendrocytes, revealing an unexpected involvement of immunological molecules.

Expression of Fc receptor for immunoglobulin M in oligodendrocytes and myelin of mouse central nervous system

Recent advances in neuro-immunology are beginning to elucidate several essential roles of the humoral immunity in both repair and pathogenesis of central nervous system diseases. Immunoglobulin M (IgM) was reported to accelerate the rate of remyelination in a demyelinating disease model, while intrathecal IgM synthesis was shown to predict a more worse disease course in a human demyelinating disease, multiple sclerosis. Molecular mechanisms for either of these IgM functions remain to be studied. Here we report that a recently-found Fc receptor for IgM, namely Fcalpha/muR, is expressed in oligodendrocytes, their precursor cells, and myelin. These expressions were confirmed by immunocytochemistry of cultured cells, Western blot analysis of myelin fractions, and also by immunohistochemistry of mouse forebrains at different ages. Our findings suggest a possible direct interaction between IgM and Fcalpha/muR expressed in oligodendrocytes and myelin.

CNS myelinogenesis in vitro: myelin basic protein deficient shiverer oligodendrocytes

The shiverer mutant mouse is an autosomal recessive mutant characterized by incomplete myelin sheath formation in the central nervous system (CNS). Such mice contain a deletion in the MBP gene, do not produce MBP proteins, and have little or no compact myelin in the CNS. To investigate the myelin sheath formation in shiverer mutant mice resulting from the absence of compact myelin, firstly we developed new methods for generating oligodendrocyte precursor cells (OPCs) from an E17 mouse brain, and examined homozygous shiverer (shi/shi) OPCs with respect to myelinogenesis in vitro. After treatment of shi/shi OPCs in vitro with PDGF or bFGF, proliferation of shi/shi OPCs was enhanced similar to that observed in wild-type OPCs. The majority of cells from the shiverer mutant mouse, however, remained as A2B5-immunoreactive early OPCs. To determine which molecular events affect the differentiation of shi/shi OPCs, we determined the signaling pathway that could be responsible for activating myelin sheath-specific proteins. We found that the developmental schedule of shi/shi OPCs in vitro was accelerated by the addition of cyclic AMP analogs, dibutyryl cAMP (dbcAMP). Treatment of shi/shi OPCs with dbcAMP had significant effect on the differentiation of OPCs that became MAG-expressing oligodendrocytes. To further determine the possible mechanism involved in the activation of MAG by dbcAMP, we examined the cAMP-dependent signaling cascades. The activation of JNK was markedly stimulated by treatment with dbcAMP, and the phosphorylation of transcription factor ATF-2 was also stimulated by dbcAMP. We demonstrated that the MAG-positive shi/shi oligodendrocytes extend processes around axons and finally covered the axon, this was clearly observed by immunocytochemistry of shi/shi oligodendrocyte-DRG cocultures. These results suggest that ATF-2 coupled to specific signal transduction cascades plays an important regulatory role in MAG expression at a specific stage of shi/shi oligodendrocyte differentiation, and OPCs grow to become myelin-forming cells with numerous cell processes that wraps around an axon to form a thin myelin sheath.

Myelin basic protein is necessary for the regulation of myelin-associated glycoprotein expression in mouse oligodendroglia

Myelin-associated glycoprotein (MAG) has currently been proposed to be a possible igniter of myelination in the central nervous system. We propose here that myelin basic protein (MBP) is prerequisite, which is more diffusely expressed than MAG in early stages of myelination. MBP-deficient mice show significant reduction of MAG-positive immature oligodendroglia at early stages of myelination, although significant increase of such cells is noted in the adult. MBP/Fyn-double deficient adult mice also show moderate increase of the same type of immature glia, but to a lesser degree than MBP-deficiency alone. The present study suggests that MBP is required for the regulation of MAG expression in oligodendroglia, involving Fyn therein. We discuss the possibility that hitherto unknown molecule, not MAG, may be in responsible for the ignition of the myelination.

Fyn tyrosine kinase participates in the compact myelin sheath formation in the central nervous system

The cellular mechanisms for spiral wrapping and compaction of myelin sheaths by oligodendrocytes are not known yet. In this study, we examined the role of fyn tyrosine kinase, which could be responsible for molecular events during the stage of myelination in the CNS. Western blot and immunohistochemical analyses revealed that fyn-deficient mice have significantly lower levels of myelin basic protein (MBP), which is required for intracellular membrane adhesion parts so-called major dense line (MDL) and thought to be essential for the stability of myelin sheath. Electron microscopy verified that the myelin ultrastructure could be used to distinguish fyn-deficient mice from wild-type mice, showing a thin and redundant myelin sheath in the corpus callosum. Further, the electron-dense 'major' line in myelin from the purified myelin fractions remained condensed, and myelin compaction was split opened in fyn-deficient mice. To determine whether there was a change in the microheterogeneity of MBP due to a post-translational event we first investigated peptidylarginine deiminase (PAD), which is an enzyme that converts arginine residues in peptides to citrulline residues. PAD immunoreactivity was observed both in the myelin from fyn-deficient and wild-type mice. By Western blot analysis we found an increase of the citrullined form of MBP. In addition, MBP from fyn-deficient mice did weakly induce vesicle aggregation properties of MBP-mediated adhesion. We concluded that although oligodendrocytes from fyn-deficient mice are able to wrap around the axon, they are unable to form compact myelin due to decreased MBP level and the presence of increased citrullinated MBP.

Monoclonal antibody 14F7, which recognizes a stage-specific immature oligodendrocyte surface molecule, inhibits oligodendrocyte differentiation mediated in co-culture with astrocytes

Cells at an intermediate stage of oligodendrocyte lineage are not only well characterized by biochemical studies but also are likely to relate to the outcome of physiological events. To elucidate the molecular events leading to the development of oligodendrocyte lineage cells, we have raised monoclonal antibodies against stage-specific immature oligodendrocytes, which have previously been isolated by a novel oligodendrocyte-lineage cell culture technique (Sakurai et al.: J Neurosci Res 52:17-26, 1998). We have isolated a mouse monoclonal antibody termed 14F7 which predominantly labels stage-specific immature oligodendrocytes and have found that the expression of 14F7 immunoreactivity in the developing neonatal rat forebrain is closely associated with cells expressing the oligodendrocyte progenitor marker A2B5 and to immature oligodendrocyte expressing O4 antigen. 14F7+ cells were distributed in the ventricular and subventricular zone and the nearby forming corpus callosum as non-myelinating cells. In contrast to cell culture observations, 14F7+ cells were seen only in oligodendrocyte lineage cells. For instance, dissociated cell culture studies indicated that 14F7 labels a cell surface molecule, and its cellular distribution is coincident with all of O4+ cells and A2B5+ cells, and even A2B5- cells. By contrast, 14F7-positive cells did not label astrocytes and, furthermore, did not label myelin basic protein (MBP)-positive oligodendrocytes. 14F7 recognized a 48-kDa protein on sodium dodecyl sulfate polyacrylamide gel electrophoresis. 14F7 immunoreactivity was detectable in rat brain as early as embryonic day 18. Furthermore, in these cells, the total time for differentiation was extended, and on maturation, these cells subsequently expressed an array of myelin-specific proteins, which normally occurs by direct contact with type-1 astrocytes. However, in the presence of 14F7, stage-specific oligodendrocytes co-cultured with astrocytes completely failed to express MBP. These data suggest that the 14F7 antigen is a novel cell surface molecule that is expressed in the intermediate stage of oligodendrocyte-lineage cells, and it is expected that it regulates the differentiation of oligodendrocyte throughout development.

Differentiation of oligodendrocyte occurs in contact with astrocyte

We have generated stage-specific oligodendrocytes, which are identified as immature oligodendrocytes by the expression of specific markers. These cells were generated by using 3 types of intrinsic and extrinsic factors for influencing the characteristics of oligodendrocyte-lineage cells. The factors included 10% serum in the medium to induce cell proliferation, bFGF in serum-free medium to increase survival and induce differentiation, and 0.25% trypsin to remove nonoligodendrocyte lineage cells. We have also demonstrated that it is possible to supply a huge amount of homogeneous populations of stage-specific immature oligodendrocytes after 35 days' culture. The maturation of these cells is controlled by interacting with astrocytes in vitro, resulting in the expression of MBP isoforms (14.0 and 18.5 kDa) that may participate in mature oligodendrocyte membrane compaction.