Structure and developmental regulation of Golli-mbp, a 105-kilobase gene that encompasses the myelin basic protein gene and is expressed in cells in the oligodendrocyte lineage in the brain

Transcriptional control in myelinating glia: flavors and spices

Transcriptional control in myelinating glia is often described in terms of a handful of trans-acting proteins with preferential expression in these cells. An equally valid approach is the identification of cis-acting elements in genes, which are specifically transcribed in myelinating glia. Regulatory regions of several myelin genes have been analyzed in transgenic animals, transient transfections and in vitro. In some cases, these studies have identified regions responsible for glial expression within the promoters or immediate upstream regions. Other myelin genes possess promoters, which simply secure basal levels of transcription, but do not contain glia-specific cis-acting elements. Promoters of myelin genes also differ strongly in other respects. They either contain a TATA-box or are TATA-less and GC-rich. They exhibit multiple transcription initiation sites or a single strong one. Binding sites for general transcription factors, such as NF-I, Sp1, and CAAT-box binding proteins, and for downstream effectors of major signaling pathways are found in them in abundance. In agreement, members of the AP-1, CREB, STAT, and NF-kappaB families are well-described components of the transcription machinery in myelinating glia. Together with several members of the nuclear receptor family, they are an intrinsic part of the transcriptional control in myelinating glia.

p-Cresol sulfate is the dominant component of urinary myelin basic protein like material

Multiple sclerosis (MS) is clinically heterogeneous and has an uncertain natural history. A high priority for more effective treatment of MS is an objective and feasible laboratory test for predicting the disease's course and response to treatments. Urinary myelin basic protein (MBP)-like material (MBPLM), so designated because it is immunoreactive as a cryptic epitope in peptide 83-89 of the human MBP molecule of 170 amino acids, is present in normal adults, remains normal in relapsing-remitting, but increases in progressive MS. In the present investigation, MBPLM was purified from urine and characterized. p-Cresol sulfate is the major component of urinary MBPLM. This conclusion is based on the following: (1) MBPLM and p-cresol sulfate both have a mass of 187 on negative scans by electrospray ionization mass spectrometry, the same fragments on tandem mass spectrometry of 80 (SO(-)(3)) and 107 (methylphenol), and similar profiles on multiple reaction monitoring; (2) (1)H and (13)C nuclear magnetic resonance spectroscopy revealed identical spectra for MBPLM and p-cresol sulfate; (3) purified p-cresol sulfate reacted in parallel with MBP peptide 83-89 in the same radioimmunoassay for MBPLM; and (4) p-cresol sulfate has the same behavior on preparative HPLC columns as urinary MBPLM. The unexpected immunochemical degeneracy permitting a cross-reaction between p-cresol sulfate and a peptide of an encephalitogenic myelin protein is postulated to be based on shared conformational features. The mechanisms by which urinary p-cresol sulfate, possibly derived from tyrosine-SO(4), reflects progressive worsening that is disabling in MS are unknown.

GFAP-positive and myelin marker-positive glia in normal and pathologic environments

The data herein demonstrate that in addition to the well-characterized myelin marker-positive, glial fibrillary acidic protein (GFAP)-negative, membrane sheet-bearing oligodendrocytes, another type of myelin marker-positive, process-bearing glia exists in normal and pathologic conditions. This second type of myelin marker-positive glia expresses GFAP, and therefore these cells have been referred to as mixed phenotype glia. Although mixed phenotype glia have been documented previously, their identity and function have remained a mystery. The goal of this immunocytochemical study was to further characterize these cells. Using the MBPlacZ transgenic mouse in which beta-galactosidase is under the control of the myelin basic protein (MBP) gene promoter, GFAP-positive/beta-galactosidase-positive and myelin/oligodendrocyte-specific protein (MOSP)-positive/beta-galactosidase-positive cells were detected in subcortical white matter and in perivascular locations within cerebral white and gray matter. In cultures prepared from highly enriched myelin marker-positive immature glia, mixed phenotype glia were detected that were GFAP-positive and either MOSP-, MBP-, O1-, and O4-positive. The expression of multiple myelin markers by mixed phenotype glia may suggest that these cells are of oligodendrocyte origin. Increased numbers of MOSP-positive/GFAP-positive mixed phenotype glia were detected in sections from adult hypomyelinated brain from shiverer, quaking, and PKU mice compared to myelinated control adult mouse brain. Similarly, cultures from control brain exposed to elevated pH for 2-3 weeks showed dramatically increased numbers of mixed phenotype glia (80%) compared to control (<10%). Increased numbers of mixed phenotype glia also were detected in shiverer cultures (40%). Since increases in the number of mixed phenotype glia occur in shiverer, quaking, and PKU mouse brain, these data suggest that mixed phenotype glia contribute to gliosis in pathologic white matter.

Myelin basic protein gene dosage effects in the PNS

Myelin basic protein (MBP) plays an essential adhesive role in the formation of compact myelin in the central nervous system (CNS), but not in the peripheral nervous system (PNS). Morphologic data suggest that MBP controls the number of cytoplasmic channels or Schmidt-Lanterman incisures (SLI) present in PNS myelin. The levels of connexin-32 (Cx32) and myelin-associated glycoprotein (MAG), two components of the incisures, are inversely proportional to the levels of MBP in sciatic nerves of mice affected by the shiverer (shi) mutation, while protein zero (P0) and peripheral membrane protein 22 (PMP22), two structural components of compact myelin, remain constant. The levels of P0, PMP22, Cx32, and MAG mRNA do not vary in relationship to the levels of MBP. This indicates that MBP exerts its effect on Cx32 and MAG at a posttranscriptional level and suggests a new function for MBP in regulating gene expression in the PNS.

Retrovirus mediated gene transfer of the self antigen MBP into the bone marrow of mice alters resistance to experimental autoimmune encephalomyelitis

Experimental autoimmune encephalomyelitis (EAE) is a prototypic model of organ specific autoimmunity. MHC class II restricted T-cells directed against myelin basic protein (MBP) have been shown to cause EAE in susceptible strains of mice. We have asked whether the introduction of a gene encoding an autoantigen (MBP) into the hematopoetic stem cells of mice would result in tolerance to that protein. We have introduced cDNA encoding the 21.5 kDa isoform of MBP into the hematopoetic stem cells of B10.PL (73NS), SJL, and B10 mice by retrovirus-mediated gene transfer. Our experiments show expression of proviral MBP in peripheral blood and thymus following transplantation of genetically modified stem cells. Such expression does not result in deletion of MBP-specific T cells or tolerance to MBP, nor does it alter susceptibility to MBP-induced EAE in susceptible strains B10.PL and SJL. However, retrovirus-mediated gene transfer resulted in resistant B10 mice developing mild EAE. This report demonstrates that autoreactive MBP-specific T cells can be selected in the presence of endogenous antigen or an MBP-encoding retrovirus.

Productive measles virus brain infection and apoptosis in CD46 transgenic mice

Measles virus (MV) infection causes acute childhood disease, associated in certain cases with infection of the central nervous system (CNS) and development of neurological disease. To develop a murine model of MV-induced pathology, we generated several lines of transgenic mice ubiquitously expressing as the MV receptor a human CD46 molecule with either a Cyt1 or Cyt2 cytoplasmic tail. All transgenic lines expressed CD46 protein in the brain. Newborn transgenic mice, in contrast to nontransgenic controls, were highly sensitive to intracerebral infection by the MV Edmonston strain. Signs of clinical illness (lack of mobility, tremors, and weight loss) appeared within 5 to 7 days after infection, followed by seizures, paralysis, and death of the infected animals. Virus replication was detected in neurons from infected mice, and virus was reproducibly isolated from transgenic brain tissue. MV-induced apoptosis observed in different brain regions preceded the death of infected animals. Similar results were obtained with mice expressing either a Cyt1 or Cyt2 cytoplasmic tail, demonstrating the ability of different isoforms of CD46 to function as MV receptors in vivo. In addition, maternally transferred immunity delayed death of offspring given a lethal dose of MV. These results document a novel CD46 transgenic murine model where MV neuronal infection is associated with the production of infectious virus, similarly to progressive infectious measles encephalitis seen in immunocompromised patients, and provide a new means to study pathogenesis of MV infection in the CNS.

Distinct levels of regulation in organ-specific autoimmune diseases

Immune regulatory interactions have been largely attributed to antagonistic T helper cell subsets whose cytokines are mutually inhibitory (Th1 vs. Th2). Here we emphasize two additional levels of regulation: the first involves the recognition of portions of antigen receptors of effector T cells, resulting in the induction of both CD4 and CD8 regulatory populations, capable of diminishing the responses by the pathogenic effector itself. The second includes a collection of cell populations found constitutively in all individuals whose specificity for antigen, if any, is being currently investigated. These two additional types of interaction involve cells belonging to a functional regulatory subset and include contributions from both innate and adaptive mechanisms of immune regulation. The answers to many quandaries in autoimmune disease may be sought by seeking to engage these lesser-understood regulatory populations.

Induction of myelin gene expression in Schwann cell cultures by an interleukin-6 receptor-interleukin-6 chimera

Expression of myelin basic protein (MBP) and Po gene products is induced during the final postnatal maturation of Schwann cells and reinduced during nerve regeneration. We show that a chimeric protein containing interleukin-6 fused to its soluble receptor (IL6RIL6 chimera) induces MBP and Po RNAs and proteins in cultures of dorsal root ganglia (DRG) from 14 day old mouse embryos. Activation of gp130 signaling by IL6RIL6 appears comparable to cyclic AMP elevating agents to induce the myelin gene products in DRG and in pure Schwann cell cultures.

Cutting Edge: Myelin Basic Protein-Specific Cytotoxic T Cell Tolerance Is Maintained In Vivo by a Single Dominant Epitope in H-2k Mice

Multiple sclerosis (MS) is believed to be an autoimmune disease mediated by T cells specific for CNS Ags. MS lesions contain both CD4+ and CD8+ T lymphocytes. The contribution of CD4+ T cells to CNS autoimmune disease has been extensively studied in an animal model of MS, experimental autoimmune encephalomyelitis. However, little is known about the role of autoreactive CD8+ cytotoxic T cells in MS or experimental autoimmune encephalomyelitis. We demonstrate here that myelin basic protein (MBP) is processed in vivo by the MHC class I pathway leading to a MBP79–87/Kk complex. The recognition of this complex by MBP-specific cytotoxic T cells leads to a high degree of tolerance in vivo. This study is the first to show that the pool of self-reactive lymphocytes specific for MBP contain MHC class I-restricted T cells whose response is regulated in vivo by the induction of tolerance.

Candidate autoantigens in multiple sclerosis

Multiple sclerosis is an inflammatory demyelinating CNS disease of putatively autoimmune origin. Novel models of experimental autoimmune encephalomyelitis (EAE) have demonstrated that T cells specific for various myelin and even nonmyelin proteins are potentially encephalitogenic. The encephalitogenic T cell response directed against different CNS antigens not only determines the lesional topography of CNS inflammation but also the composition of the inflammatory infiltrates. The heterogeneity of the lesional distribution seen in EAE might therefore be useful for the understanding of the various clinical subtypes seen in MS. In this review the possible candidate autoantigens in MS are discussed with special regard to the human T cell and B cell responses against various myelin and nonmyelin proteins.

The expression of myelin protein mRNAs during remyelination of lysolecithin-induced demyelination

To gain insights into the mechanisms of myelin repair in the CNS and to establish the extent to which this process resembles myelination in development we have examined the patterns of expression of transcripts of the major myelin proteins, myelin basic protein (MBP) and proteolipid protein (PLP) during remyelination of lysolecithin-induced demyelination in the adult rat spinal cord. Injection of 1 microliter 1% lysolecithin into the dorsal funiculus caused a dramatic decrease in levels of MBP exon 1 and MBP exon 2-containing transcripts and PLP/DM20 transcripts. Between 10 and 21 days post-lesion induction there was a gradual increase in levels of expression of all transcripts, which had returned to levels associated with normally myelinated spinal cord white matter at 21 days. These increases in levels of expression corresponded to the appearance of remyelinated axons, detected on toluidine blue-stained resin sections. Foci of high levels of expression occurred in regions of the lesion in which new myelin sheath formation was occurring, although the level of expression throughout the lesion never exceeded levels associated with myelin sheath maintenance in normal white matter due to the asynchronous pattern of remyelination. The changes in levels of expression of MBP exon 2 closely followed those of MBP exon 1. Our results indicate that (i) myelin protein gene expression associated with myelinogenesis during remyelination follows a similar pattern to that of myelinogenesis during development and that (ii) in rat models of demyelination changes of expression of MBP exon 1 and exon 2-containing transcripts are of equal value, an observation relevant to quantifying the effects of putative remyelination-enhancing strategies using the lysolecithin model.

Rapid release and unusual stability of immunodominant peptide 45-89 from citrullinated myelin basic protein

Myelin basic protein (MBP) exists in a population of isoforms and isomers. The 18.5 kDa MBP-C1, the main human adult isoform, has 170 residues and is relatively unmodified, whereas the same isoform can be citrullinated on six arginine residues to create the MBP-C8 (MBP Cit6) isomer. MBP Cit6 dominates in MS brain, accounting for 45% rather than 25% of the population of MBP isomers. In the fulminant form of MS, known as Marburg's Disease, 18 of the 19 arginines in MBP are citrullinated (MBP Cit18). Citrullination of MBP could lead to instability of myelin or limited remyelination. In this investigation, the susceptibilities to degradation by cathepsin D of MBP Cit6 and MBP-C1, both from normal and MS brain tissue, and Marburg MBP Cit18 were compared. The pattern of digestion was similar, and no differences of corresponding isomers in normal and MS brain were noted. However, normal MBP Cit6 was degraded 10-fold more rapidly than MBP-C1, and MBP Cit18 was degraded even more rapidly. MBP peptide 45-89 was preserved regardless of isomer type or source. Its generation was directly related to the citrulline content of the MBP substrate being 4 times faster in normal MBP Cit6 and 35 times faster in Marburg MBP Cit18 than in normal MBP-C1. Peptide 45-89 from a citrullinated MBP exhibited more deamidation, and, regardless of source, showed an alpha-helix structure in a lipid mimetic environment. We postulate that the generation of MBP peptides, including those that are dominant and encephalitogenic, is directly related to deimination of arginine to citrulline in MBP.

Highly basic myelin and oligodendrocyte proteins analyzed by NEPHGE-two-dimensional gel electrophoresis: recognition of novel developmentally regulated proteins

Two-dimensional polyacrylamide gel electrophoresis (2D-PAGE) provides high resolution separation of proteins and offers a powerful method for their identification and characterization. Since many myelin-specific proteins are highly basic, they cannot readily be analyzed by standard isoelectric focusing (IEF)-2D-PAGE that affords separation primarily in the isoelectric points (pI) range of 4-8. An alternative method, nonequilibrium pH gradient electrophoresis (NEPHGE)-2D-PAGE, can provide excellent resolution of highly basic proteins. In the present study, we have optimized the NEPHGE-2D-PAGE protocol for the analysis of myelin proteins with basic pIs, and provide a NEPHGE-2D-PAGE map based on size, pI, and immunoreactivity (Western blot) of myelin basic protein (MBP), 2', 3'-cyclic-nucleotide 3'-phosphodiesterase (CNP), myelin proteolipid protein (PLP), and its smaller spliced variant DM20, myelin/oligodendrocyte glycoprotein (MOG) and oligodendrocyte-specific protein (OSP). We have also demonstrated, by analyzing metabolically radiolabeled oligodendrocytes in culture at specific stages of the developmental lineage, the developmentally up-regulated expressions of several undefined, oligodendrocyte, basic membrane proteins during oligodendrocyte differentiation. We suggest that this approach offers an important tool for identifying and characterizing the plethora of uncharacterized myelin proteins.

Golli-Induced Paralysis: A Study in Anergy and Disease

The Golli-MBP transcription unit contains three Golli-specific exons as well as the seven exons of the classical myelin basic protein (MBP) gene and encodes alternatively spliced proteins that share amino acid sequence with MBP. Unlike MBP, which is a late Ag expressed only in the nervous system, Golli exon-containing gene products are expressed both pre- and postnatally at many sites, including lymphoid tissue, as well as in the central nervous system. To investigate whether Golli-MBP peptides unique to Golli would result in neurological disease, we immunized rats and observed a novel neurological disease characterized by mild paralysis and the presence of groups of lymphocytes in the subarachnoid space but not in the parenchyma of the brain. Disease was induced by Th1-type T cells that displayed an unusual activation phenotype. Primary stimulation in vitro induced T cell proliferation with increased surface CD45RC that did not become down-regulated as it did in other Ag-stimulated cultures. Secondary stimulation of this CD45RChigh population with Ag, however, did not induce proliferation or IL-2 production, although an IFN-γ-producing population resulted. Proliferation could be induced by secondary stimulation with IL-2 or PMA-ionomycin, suggesting an anergic T cell population. Cells could adoptively transfer disease after secondary stimulation with IL-2, but not with Ag alone. These responses are suggestive of a chronically stimulated, anergic population that can be transiently activated to cause disease, fall back into an anergic state, and reactivated to cause disease again. Such a scenario may be important in chronic human disease.

Two neuronal cell lines expressing the myelin basic protein gene display differences in their in vitro survival and in their response to glia

We have generated two conditionally immortalized neuronal cell lines from primary cultures of embryonic day 13 (E13) and postmitotic (postnatal day 0; P0) cortical neurons transformed with the temperature-sensitive SV-40 large-T antigen. Two clonal cell lines (CN1.4 from E13 cultures and SJ3.6 from P0 cultures) were isolated and stable maintained in vitro. Both cell lines expressed a number of neuronal markers such as the neurofilaments, glutamic acid decarboxylase 67, neuron-specific enolase, and the BG21 isoform of the myelin basic protein gene. At 34 degrees C, the CN1.4 cell line had elaborated short processes, whereas the SJ3.6 cell line produced long processes that formed a delicate network. When these cell lines were cultured at 39 degrees C, some of the cellular processes grew longer, adopting a more mature neuronal morphology. Interestingly, at 39 degrees C, the in vitro survival of these cell lines differed significantly. Whereas the survival of CN1.4 cell line was greatly unaffected, SJ3.6 cells died soon after they were cultured at 39 degrees C. The cell death of SJ3.6 cells was accompanied by fragmentation and condensation of DNA in their nuclei, indicative of an apoptotic event. Under these conditions, SJ3.6 showed an upregulation of the p75 receptor. When this cell line was cocultured with oligodendrocytes, astrocytes, or glial conditioned media (GCM), there was a marked increase in survival. In contrast, little effect of glial cells or GCM was observed on the CN1.4 cell line. These lines appear to be useful models to study neuronal-glial interactions in addition to neuronal cell death and the effects of glial factors that promote the survival of neurons.

Myelin protein expression in lymphoid tissues: implications for peripheral tolerance

During chronic relapsing experimental autoimmune encephalomyelitis (EAE), T lymphocytes specific for myelin protein epitopes are stimulated in vivo. When epitopes are unique from the disease-initiating myelin protein epitope, this phenomenon has been termed "epitope spreading". These T-lymphocyte responses have been detected primarily in lymph node and spleen during the relapsing phase of disease. If myelin proteins are sequestered behind the blood brain barrier, a fundamental question arises: where does the in vivo stimulation of T lymphocytes occur during relapsing EAE? While it has been thought that epitope spreading may occur within the central nervous system (CNS), here we present data supporting a novel hypothesis. Epitope spreading during EAE may not occur within the CNS, but rather within lymphoid tissues. Both myelin basic protein (MBP) and proteolipid protein (PLP) are expressed at the RNA and protein level in lymph node, thymus and spleen of SJL mice with relapsing EAE. This myelin protein expression occurs within T lymphocytes, B lymphocytes and macrophages. Further, T-lymphocyte lines from SJL mice specific for the immunodominant and subdominant epitopes of MBP and PLP can recognize endogenous protein within cells derived from lymphoid tissues. Thus, immunologically relevant myelin proteins are endogenously produced and presented within lymphoid tissues. The hypothesis that epitope spreading occurs within lymphoid tissues would explain how myelin protein-specific T lymphocytes become activated outside the CNS to allow their passage through the blood brain barrier to form new CNS lesions during relapses.

Determinant spreading during experimental autoimmune encephalomyelitis: is it potentiating, protecting or participating in the disease?

During many autoimmune conditions, a T-cell response initially focused to a self-antigen evolves towards the recruitment of T cells to multiple antigenic determinants. Here we discuss whether such determinant spreading involves T cells activated in the peripheral lymphoid organs, or alternatively, whether the diversification occurs after infiltration of the initiating T cells into the target organ, for example, into the central nervous system during experimental autoimmune encephalomyelitis, a prototype for multiple sclerosis. The expression of myelin antigens in the thymus and spleen may not only contribute to the induction of tolerance but also to determinant spreading. In this case, the outcome of in vivo diversification may ultimately be determined by the balance between type 1 and type 2 responses to antigenic determinants derived from myelin components. Thus, spreading T cells could modulate disease progression positively or negatively, depending upon the nature of the accompanying cytokine secretion profile.

Intrathymic expression of genes involved in organ specific autoimmune disease

Insulin, thyroglobulin and myelin basic protein (MBP) are implicated as autoantigens in the autoimmune diseases, insulin-dependent diabetes mellitus (IDDM), autoimmune thyroid-disease and multiple sclerosis. Self tolerance to these antigens, until recently only thought to be present extrathymically, is generally considered to be maintained by 'peripheral' mechanisms, such as clonal anergy or clonal ignorance. The techniques of reverse transcription and polymerase chain reaction (RT-PCR) were used to investigate the intrathymic expression of these genes. Expression was examined in mRNA isolated from complete adult rat thymus, various mouse thymic cell-types isolated from fetal thymic-organ cultures and from neonatal-mouse thymocyte subsets. mRNA for insulin, thyroglobulin and MBP were detected in unfractionated adult rat and embryonic mouse thymus. Rat thymus expressed both insulin I and II, while mouse thymus only expressed insulin II. Thyroglobulin and MBP, but not insulin mRNA were detected in mouse MHC class II+ thymic epthelial cells and class II+ dendritic cells and in certain thymocyte subsets. The presence of insulin, thyroglobubin and MBP mRNA in the thymus has important implications for the development of the T-cell repertoire, particularly for the mechanisms of tolerance that prevent autoreactivity to these antigens in healthy individuals.

T-cell responses to myelin basic protein in normal and MBP-deficient mice

BALB/c mice are resistant to the development of experimental autoimmune encephalomyelitis (EAE) after immunization with myelin basic protein (MBP). Previous studies of BALB/c mice suggest that MBP-specific T-cells can eventually be cloned from these mice, although they are either initially present in very low frequencies or are functionally anergic. To determine what role endogenous MBP expression plays in shaping the BALB/c T-cell repertoire, MBP-deficient BALB/c mice were constructed by breeding the shiverer (shi/shi) mutation onto the BALB/c background. These mice lack all conventional isoforms of MBP due to a deletion of MBP exons 3-7. Studies of the MBP-directed response of these mice suggest that endogenous MBP expression is directly responsible for EAE resistance in BALB/c mice, by quantitatively affecting expression of the T-cell repertoire. In contrast to wild-type BALB/c T-cells, uncloned T-cells from BALB/c shi/shi mice immunized with MBP proliferate in vitro to MBP and MBP peptides 59-76 and 89-101 and are able to induce severe EAE upon transfer to BALB/c recipients expressing MBP.

Overexpression of a minor component of myelin basic protein isoform (17.2 kDa) can restore myelinogenesis in transgenic shiverer mice

Shiverer (shi) mice, which are neurologically mutant, lack a large portion of the gene for the myelin basic proteins (MBPs), have virtually no myelin in their central nervous system (CNS), and shiver, undergo seizures, and die early. At least five types of MBPs (21.5, 18.5, 17.3, 17.2 and 14.0 kDa) are known to be generated through alternative splicing from a single MBP gene. We have produced transgenic shi mice carrying a cDNA encoding mouse 14-kDa MBP isoform, the most abundant form of MBPs, under control of a mouse MBP gene promoter, and showed that expression of the 14-kDa MBP can restore CNS myelination. To test whether the 17.2-kDa MBP isoform, one of the minor components of MBPs, can also elicit myelination in homozygous shi mutants, we produced seven independent transgenic shi mice carrying cDNA encoding the mouse 17.2-kDa MBP isoform, and the transcription of which was driven by a mouse MBP gene promoter. The axons in the cerebellum of one transgenic line, which exhibited the highest expression of transgene-derived mRNA ( approximately 50% of the level of total MBP mRNA in the normal mouse brain), were myelinated. This mouse exhibited nearly normal behavior. These findings indicate that the 17.2-kDa MBP isoform, even when the only 17.2-kDa MBP isoform is present, has the ability to elicit CNS myelination in transgenic shi mice. This transgenic strategy will be useful for elucidating the role of each type of MBP isoform in CNS myelinogenesis.

Identification and cloning of a brain autoantigen in neuro-behavioral SLE

In murine models of SLE, particular patterns of abnormalities of social interaction and memory collectively known as neurobehavioral dysfunction (NBD) correlate with the occurrence of brain reactive autoantibodies. Study of the immunopathogenic effects of these antibodies has been limited by the absence of isolated autoantibodies and antigens. In order to identify the molecular targets, we isolated autoantibodies highly specific for brain plasma membranes from MRL/lpr mice. After immunoscreening a brain expression library with these brain specific autoantibodies, we identified a single cDNA clone of unique sequence and relevant anatomic distribution. Transcript for this cDNA is wide spread among mammalian species but appears to be present only in the brain. Addition features, suggesting this cDNA is pertinent for further study include (1) the expressed protein, called lupus brain antigen 1, reacts with the screening immunoglobulins as well as immunoglobulins from other strains of murine neuro-SLE not used to screen the library, but not with immunoglobulins from normal mice, (2) the transcript distribution within the brain is similar to immunochemical localization of binding of the spontaneous autoantibodies and (3) the localization of transcript within the brain, in the hippocampus, hypothalamus an cingulate gyrus, corresponds to anticipated anatomical regions of clinical dysfunction. Further, the transcript is a large, potentially structural molecule of unique sequence. Antibodies to this molecule may mediate changes in behavior either by direct interactions with the cognate antigen or by indirect influences through neuro-endocrine axes.

Myelin basic protein in cerebrospinal fluid and other body fluids

Myelin basic protein (MBP) or a fragment thereof may enter cerebrospinal fluid (CSF) and other body fluids in an etiologically nonspecific fashion to provide information about the status of central nervous system (CNS) myelin damage. MBP immunochemically detected is referred to as MBP-like material (MBPLM). The clinical utility of the assay for MBPLM in CSF is to document the presence, continuation, or resolution of CNS myelin injury. The analysis of CSF for MBPLM is subject to many variables, among which are the antisera and the form of the assay utilized. The dominant epitope of CSF MBPLM is in the decapeptide of 80-89 from the intact MBP molecule of 170 residues. Normally, CSF has no detected MBPLM. Following an acute relapse of MS, MBPLM rises quickly in the range of ng/ml and rapidly declines and disappears. The presence of MBPLM in CSF in chronic and progressive phases of the disease is unusual, but it may sometimes be detected in low levels, depending on the assay used for detection. The level of CSF MBPLM is related to both the mass of CNS myelin damage and how recently it occurred. The level of CSF MBPLM rarely is elevated in optic neuritis. The level of CSF MBPLM is unrelated to CSF protein level, level of IgG, presence of oligoclonal bands or pleocytosis. CSF MBPLM has the potential of serving as a marker of therapeutic effectiveness in MS and does have predictive value for response to glucocorticoids given for worsening of disease. The detection of MBPLM in body fluids other than CSF would be of great value because of the resulting improved feasibility for objectively monitoring the natural history of MS and response to therapy. Studies on blood have yet to produce a valid assay of MBPLM. Urinary MBPLM, though different in its features from that in CSF, may provide a correlate, not with acute demyelination in MS as is the case for CSF, but with progression of disease.

STAR, a gene family involved in signal transduction and activation of RNA

A new subfamily of KH-domain-containing RNA-binding proteins is encoded by genes that are conserved from yeast to humans. Mutations with interesting developmental phenotypes have been identified in Caenorhabditis elegans, Drosophila and mouse. It is hypothesized that these bifunctional proteins provide a rich source of interesting molecular information about development and define a new cellular pathway that links signal transduction directly to RNA metabolism.

An alternatively spliced, 5'-truncated MAP1B isoform is expressed in the developing chick nervous system

Our laboratory has previously characterized a keratan sulfate proteoglycan, named claustrin, and shown by molecular cloning that claustrin and the mouse MAP1B protein share high homology, with claustrin representing a 5'-truncated fragment of MAP1B. In the present study, we examine further the relationship between claustrin and MAP1B, and also describe the isolation of a cDNA encoding the 3'-region of MAP1B, which shares 3'-untranslated sequence, but not coding sequence, with claustrin. We call this partial cDNA 3'-MAP1B-related clone (3'-MRC), since it is homologous to the 3'-region of the mouse MAP1B sequence. We show by Northern analysis that distinct mRNAs are recognized by the claustrin and 3'-MRC cDNAs, and by RT-PCR that mRNAs encoding these distinct MAP1B-related molecules are present in embryonic chick brain and cardiac and smooth muscle. Our data also suggest a higher level of expression of claustrin mRNA in astrocyte cultures, when compared to 3'-MRC. Our data therefore provide new evidence that alternatively spliced variants of MAP1B are expressed in brain, and that at least one of these variants encodes the claustrin proteoglycan.

Golli-MBP proteins mark the earliest stages of fiber extension and terminal arboration in the mouse peripheral nervous system

The Golli-myelin basic protein (MBP) transcription unit gives rise to two sets of products. One set (i.e., the MBPs) is expressed exclusively in myelin forming cells and the other set (i.e., the golli isoforms) is expressed in both oligodendrocytes and neurons in the CNS. The two major golli proteins, generated from RNAs transcribed from the most upstream promoter of the gene, contain MBP peptide sequences in their C-terminal halves and are, therefore, structurally and immunologically related to the MBPs. We have examined the distribution and localization of golli proteins in the mouse peripheral nervous system (PNS) using immunocytochemistry with a golli-specific antibody. Golli immunoreactivity was first observed in sensory and motor fibers of the mouse at E11 during fiber tract extension, but prior to the maturation of terminal connections. Once neuromuscular junctions had formed, golli immunoreactivity appeared in motor endplates and persisted to the latest age examined, P60. Golli immunoreactivity was also observed in the cell bodies and processes of the dorsal root ganglia throughout development. Strong staining in the PNS of the dysmyelinating mutant shiverer suggested that the major golli protein in peripheral fibers was the BG21 isoform. Interestingly, golli immunoreactivity was also found in adrenal chromaffin cells, which share a common neural crest derivation with other postganglionic neurons that express golli protein. These results suggest that in addition to its role in early forming neuronal systems of the CNS, golli protein also plays a role in the early development and maintenance of neurons in the PNS.

Two proteins bind to a novel motif in the promoter of the myelin basic protein gene from mouse

The box 1 and 2 motif of the myelin basic protein (MBP) promoter is a potential regulatory sequence of the MBP transcription unit. A DNA fragment that contained the sequence of the box 1 and 2 motif from mouse was synthesized, and its protein binding properties were examined by gel-shift assays. The box 1 and 2 probe and nuclear extracts from mouse brain generated a pattern of six major DNA-protein complexes (a, b, c, d, e, and f). The box 1 and 2 probe and nuclear extracts from oligodendrocyte-like glioma cells 1C10 generated a pattern of DNA-protein complexes that exhibited only complexes a, b, e, and f. Complex b generated by extracts from 1C10 cells, however, was very intense compared to any of the other complexes. It was determined that dephosphorylation of the proteins in nuclear extracts from 1C10 cells with acid phosphatase significantly altered their DNA binding properties. Two proteins of minimum M, approximately 32 and approximately 38 kDa (MBP32 and MBP38) that bind to the box 1 and 2 motif were identified in these nuclear extracts by using a UV crosslinking method. MBP32 and MBP38 are found in cell types and tissues known to express the golli transcription unit of the golli-MBP gene complex and may be involved in the modulation of the MBP unit in those cells.

The active transport of myelin basic protein into the nucleus suggests a regulatory role in myelination

The myelin basic proteins (MBPs) are a set of membrane proteins that function to adhere the cytoplasmic leaflets of the myelin bilayer. During oligodendrocyte maturation prior to compact myelin formation, however, certain MBPs have been observed within the cell body and nucleus. We explored the parameters of the translocation of the exon II-containing MBPs (MBPexII) from the site of synthesis in the cell cytoplasm into the nucleus and in some experiments used GFP as a molecular reporter to monitor the intracellular distribution of MBP-GFP fusion proteins in living cells. We show here that the transport of MBPexII into cell nuclei is an active process, which is temperature and energy dependent, and may be regulated by phosphorylation state. Further, MBPexII can direct the entry of macromolecular complexes into cell nuclei, revealing that the exon II peptide segment may provide a nuclear localization signal (NLS), perhaps a novel one, or may induce a conformational change in the full-length protein that exposes a cryptic NLS. The MBPexII are thus very unusual in that they are plasma membrane proteins that are also targeted to the nucleus. In oligodendrocytes and Schwann cells, where the MBPs are naturally expressed, it is likely that karyophilic MBPs subserve a regulatory function in implementing the myelination program.

Differential and cell development-dependent localization of myelin mRNAs in oligodendrocytes

In oligodendrocytes (OLG), the mRNAs for the various myelin proteins localize to different intracellular sites. Whereas the confinement of myelin basic protein (MBP) mRNA to the processes of the cell has been well established, we demonstrate that most other myelin mRNA species are mainly present in the perinuclear region. Using in situ hybridization of cultured rat OLG we found that mRNAs are localized to at least three different locations: 1) to the perinuclear region [myelin-associated glycoprotein (MAG) mRNA]; 2) mainly to the processes (the mRNA for the 14-kDa isoform of MBP); and 3) to both the perinuclear region and the primary processes [2',3'-cyclic nucleotide phosphodiesterase (CNPase) and proteolipid protein (PLP) mRNAs]. Thus, depending on their primary structure, the mRNA species in OLG either remain near the nucleus or localize to primary or secondary processes before their translation. The myelin mRNA localization correlates well with that of the proteins encoded in them, as demonstrated by immunocytochemistry. Since different isoforms of MBP have different locations in transfected HeLa cells (Staugaitis et al.: J Cell Biol 110:1719-1727, 1990), we also have investigated the localization of the various mRNAs in OLG, using exon 2-minus and exon 2-specific probes in situ hybridization. The exon 2-minus MBP mRNAs are transported far into the processes, whereas exon 2-specific mRNA was only detected in the cell body. This suggests that sorting and trafficking of MBP mRNA are regulated by the presence or absence of the exon 2 sequence. Furthermore, during maturation of OLG, exon 2-plus mRNAs disappear, whereas exon 2-minus mRNAs increase. The developmentally regulated expression of exon 2-plus transcripts suggest a role of their protein products in differentiation rather than in myelination.

Alterations in the spontaneous release of dopamine and the density of the DA D2 receptor mRNA after chronic postnatal exposure to cocaine

The influence of cocaine administration on dopamine (DA) release and D2 dopamine receptor mRNA levels was examined in developing rat brain. In the rat pup, cocaine (25 mg/ kg SC) was administered daily from postnatal days 1-9 and extracellular DA measured 24 h after the last injection of cocaine, using in vivo micro dialysis. Twenty-four hours after discontinuing cocaine administration, a decrease in the extracellular concentration of DA of more than 100% was found in treated pups compared to control pups. Pups were tested on postnatal days 10-12, 20-21, or 35-36. After 1 month, basal release of DA returned to control levels. To examine the structural basis of the alteration in basal release of DA, in situ hybridization studies were performed to access the effect of chronic administration of cocaine on the mRNA encoding the D2 DA receptor. These preliminary studies, on postnatal day 10, indicate that drug treatment alters the developmental pattern of D2 mRNA. The changes in D2 mRNA expression were accompanied by delayed disaggregation of neostriatal cells and diminished growth of neostriatal neurons. These structural changes may lead to functional impairment in the development of dopamine target cells, thus altering the balance of synaptic and trophic effects of DA.

Epitope spreading occurs in active but not passive EAE induced by myelin basic protein

Using experimental allergic encephalomyelitis, EAE, as a model for the study of autoimmune demyelinating disease in the CNS, previous studies have indicated that spread may occur with respect to the specificity of T cell responses during disease. This phenomenon, known as epitope spreading, is central to therapeutic strategies in multiple sclerosis (MS). However, in EAE, the clinical course, neuropathology and immunopathogenesis vary depending upon host factors and the method of disease induction. Since passive EAE in SJL/J mice resembles MS clinically and neuropathologically, this model was chosen to study the immune phenomenon of epitope spreading. T cells specific for whole 18.5 kDa MBP were used to initiate disease since MBP or one of its naturally occurring cleavage fragments may initiate a more physiological immune response than one generated to an artificially designed synthetic peptide. While a progressive increase in T cell responsiveness specific for the immunodominant MBP 87-106 region was observed during disease, there was no evidence of either intermolecular epitope spreading to the immunodominant region of proteolipid protein (PLP) 139-151 or of intramolecular epitope spreading to the exon 2 encoded region of MBP, which is spliced out of 18.5 kDa MBP. In addition there was no shift in immunodominance toward the subdominant MBP 16-35 region during disease. In contrast during active EAE induced by MBP, epitope spreading to the immunodominant epitope of PLP, 139-151, was observed. These data demonstrate that immune responses generated during passive versus active EAE may differ, and suggest that significant epitope spreading does not occur in chronic relapsing demyelinating disease initiated with T cells specific for whole MBP in the absence of exogenous antigen, complete Freund's adjuvant and pertussis. Implications of these findings with regard to epitope spreading in MS are discussed.

Transcription of myelin basic protein promoted by regulatory elements in the proximal 5' sequence requires myelinogenesis

Myelination in the central nervous system requires synthesis by oligodendrocytes of enormous amounts of lipids and proteins for incorporation in the developing myelin membranes. To approach the regulatory events coordinating the transcriptional activation of the genes that encode myelin proteins, we examined control of the myelin basic protein (MBP) locus. MBP plays a major role in myelin compaction. During development, MBP is already expressed in mature non-myelinating oligodendrocytes. Here we show that, in transgenic animals in which the E. coli lacZ reporter gene is under the control of increasingly large portions (256, 1900 and 3200 bp) of the MBP promoter, 5' of the initiation of transcription site, reporter gene expression was initiated after myelin formation had started. This delayed expression of the transgene compared to MBP, strongly suggests that premyelinating expression is dependent on regulatory elements located outside of the 3200 bp sequence studied, while expression occurring at the time of myelin formation is dependent on the proximal promoter sequence.

Zebra finch estrogen receptor cDNA: cloning and mRNA expression

In zebra finches, estrogen is a potent hormone that masculinizes the neural circuitry controlling song during development and activates song in adulthood. However, previous studies have reported conflicting patterns of estrogen receptor (ER) expression in the song control regions. To obtain additional information about the distribution of ER in the zebra finch brain, a cDNA encoding an estrogen receptor was isolated from a zebra finch hypothalamic-preoptic area cDNA library. The 2792 bp insert contains a 1764 bp open reading frame with 5' and 3' untranslated regions of 132 bp and 896 bp, respectively. The deduced polypeptide is 589 amino acids in length and is highly homologous to the estrogen receptors of chicken (97%), rat (79%), mouse (79%), human (78%), Xenopus laevis (76%) and trout (49%). Northern blot analysis revealed three ER mRNAs expressed differentially in ovary, oviduct and telencephalon. The smallest transcript, 4.1 kb, was expressed in all three tissues, whereas larger mRNAs were expressed in ovary (7.6 kb) and oviduct (8.1 kb). In situ hybridization histochemistry revealed strong labelling in the infundibular region of the hypothalamus, preoptic area, and medial caudal neostriatum. Few or no labelled cells were found in the song control nuclei (HVC, RA, MAN or Area X). These results are consistent with previous studies that have shown ER protein and binding in hypothalamic and preoptic area and a lack of ER in most regions that control song production.

Myelin/oligodendrocyte glycoprotein (MOG) expression is associated with myelin deposition

We investigated the onset of expression of the myelin/oligodendrocyte glycoprotein (MOG) mRNA and protein in the developing mouse central nervous system. In situ hybridization on brain sections at different stages of embryonic and postnatal development showed that MOG transcripts were first detected at birth in the medulla oblongata. During the first week after birth, cells expressing MOG mRNA were located in the ventral longitudinal funiculus. During the second postnatal week, the pattern of MOG mRNA expression extended rostrally to the mid-forebrain regions and reached completion by the beginning of the third week. MOG transcription was delayed by several days with respect to myelin basic protein (MBP), and it appeared that while the MBP probe labeled both non-myelinating and myelinating oligodendrocytes, only the latter were MOG-positive. In vitro, immunocytochemical analysis of MOG protein expression, performed on myelinating cultures derived from mouse brain embryos at 15 days of gestation, confirmed the strict restriction of MOG expression to myelinating oligodendrocytes. In particular, oligodendrocytes lining up their processes along axons, but not yet having started to deposit a myelin sheath, were still MOG negative. However, in the same cultures, pseudo-myelinating oligodendrocytes (i.e., cells not associated with neurites, but forming whorls of myelin-like figures) were MOG positive. Similarly, rat CG4 cells, an oligodendrocyte-like cell line, expressed MOG only after they had extended sheet-like processes, which suggested that the activation of MOG transcription depends more on an intrinsic oligodendroglial maturation program of myelination than on a neuronal signal.

Strain-related differences in the ability of T lymphocytes to recognize proteins encoded by the golli-myelin basic protein gene

Protein products of the golli-MBP gene complex, expressed in the nervous and lymphoid systems, contain sequences in common with sequences in 'classic' MBP, expressed exclusively in the nervous system. In this report, it was determined whether T cell lines (TCLs) specific for encephalitogenic epitopes of 'classic' MBP were able to recognize sequences within golli-MBP. TCLs derived from SJL mice specific for the immunodominant 83-102 sequence and the subdominant 19-27 sequence of 'classic' MBP recognized golli-MBP J37 and BG21, respectively. In contrast, TCLs derived from PL and B10.PL mice specific for the immunodominant 1-9 sequence of 'classic' MBP did not recognize this sequence within either J37 or BG21. These strain-related differences in the ability of golli-MBP proteins to stimulate 'classic' MBP-specific TCLs are discussed with respect to a possible influence on whether the course of EAE is relapsing (SJL) or monophasic (PL and B10.PL).

Biochemistry of demyelination

The myelin sheath, a lipid-rich multilamellar membrane of relative stability, both insulates and enhances conduction in nerve axons. A notable feature of myelin-specific proteins, in particular myelin basic protein, is their susceptibility to proteolytic activity and their encephalitogenicity, which induces inflammatory demyelination in the CNS. The final common pathway of myelin breakdown in vivo is well documented and there is evidence that myelin disruption can be mediated directly by soluble (circulating) factors and for following receptor-driven phagocytosis by macrophages. However the exact mechanism(s) of demyelination in multiple sclerosis is still unresolved, both antigen-specific and--non-specific events having the potential to generate the myelinolytic process.

Expression of the myelin proteolipid protein gene in the human fetal thymus

We have analyzed human fetal thymus and spleen for expression of the proteolipid protein (PLP) gene. We demonstrate that the PLP gene is transcribed in both tissues, and that both the PLP and DM-20 mRNAs are produced. Western blot analyses revealed that both the PLP and DM-20 protein isoforms were present in the fetal thymus and spleen. Immunohistochemical analyses indicated that the PLP/DM-20 proteins were detected in cells which have the distribution and morphology of thymic macrophages. These results provide further evidence that the PLP and DM-20 proteins are expressed in cell types other than myelin forming cells and possess function(s) unrelated to myelin structure. Furthermore, these data demonstrate that the PLP and DM-20 proteins are not shielded from the immune system behind the blood-brain barrier. These observations directly impinge upon the debate concerning acquisition of tolerance and the recognition that the encephalitogenic nature of PLP in diseases, such as Multiple Sclerosis, may not simply be related to its 'sequestration' from a 'naive' immune system.

The quaking gene product necessary in embryogenesis and myelination combines features of RNA binding and signal transduction proteins

The mouse quaking gene, essential for nervous system myelination and survival of the early embryo has been positionally cloned. Its sequence implies that the locus encodes a multifunctional gene used in a specific set of developing tissues to unite signal transduction with some aspect of RNA metabolism. The quaking(viable) (qkv) mutation has one class of messages truncated by a deletion. An independent ENU-induced mutation has a nonconservative amino acid change in one of two newly identified domains that are conserved from the C. elegans gld-1 tumour suppressor gene to the human Src-associated protein Sam68. The size and conservation of the quaking gene family implies that the pathway defined by this mutation may have broad relevance for rapid conveyance of extracellular information directly to primary gene transcripts.

Membrane adhesion and other functions for the myelin basic proteins

The myelin basic proteins are a set of peripheral membrane polypeptides which play an essential role in myelination. Their most well-documented property is the unique ability to 'seal' the cytoplasmic aspects of the myelin membrane, but this is probably not the only function for these highly charged molecules. Despite extensive homology, the individual myelin basic proteins (MBPs) exhibit different expression patterns and biochemical properties, and so it is now believed that the various isoforms are not functionally equivalent in myelinating cells. We now think that while the major MBPs are intracellular adhesion molecules, some of the quantitatively less abundant isoforms that are expressed very early in development may have regulatory effects on the myelination program.

Localization and partial characterization of a 60 kDa citrulline-containing transport form of myelin basic protein from MO3-13 cells and human white matter

The localization of myelin basic proteins (MBPs) in an immortalized human-human hybrid cell line (MO3-13) formed by fusion of rhabdomyosarcoma TE671-TG6 with primary human oligodendrocytes, cultured from surgical specimens, demonstrated an intracellular localization in vesicles and vacuoles with an intricate internal membranous network and to the external surface of the cell by immunogold electron microscopy. The availability of antibodies to one of the components of MBP, i.e., the citrulline containing component ("C-8"), permitted us to localize this component of MBP to intracellular vacuoles and also on the external surface of the MO3-13 cells. Since the apposition of the external surfaces of the oligodendrocyte is responsible for the intraperiod line of the myelin sheath, localization of C-8 to the external surface of non-permeabilized cells by immunogold scanning electron microscopy is consistent with our observations that C-8 is localized to the intraperiod line of myelin (McLaurin et al.: J Neurosci Res 35:618-628, 1993). Western blots of isolated MBP from MO3-13 cells, probed with an antibody reactive with residues 130-137 of MBP, recognized a protein in the 60 kDa range. No immunoreactivity was found in the 18.5 kDa range. This 60 kDa protein also reacted with a monoclonal antibody raised with residues 70-84 of MBP, 2 different polyclonals raised with whole bovine MBP, an antibody to human MBP raised in monkeys, and the anti-citrulline antibody. These data strongly suggested that the 60 kDa protein contained MBP sequences within its primary structure. A similar protein has been isolated from human myelin-containing fractions but not from compact myelin demonstrating that the 60 kDa protein from MO3-13 cells was not an artefact related to fusion. Sequence determination of peptides obtained from enzymic and chemical cleavages revealed that the 60 kDa protein contained MBP sequences and peptides with 55-60% homology with dynamin, a protein involved in intracellular transport. These data suggest that the externalization of MBP in this cell involves transport by fusion of MBP with another protein. By sequestering MBP in a larger protein, the possibility of inducing autoimmune disease by MBP released, due to cell death, is minimized.

Developmental expression of the C1G5F2 antigen in cultured rat oligodendroglial cells

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

Myelinogenic potential of an immortalized oligodendrocyte cell line

The myelinogenic potential of an oligodendrocyte cell line (N20.1) immortalized by transformation with a temperature-sensitive retrovirus (Verity et al., J Neurochem 60:577-587, 1993) has been evaluated in a co-culture system utilizing dorsal root ganglion neurons. When N20.1 cells were placed in co-culture with dorsal root ganglion neurons at 39 degrees C, the temperature at which TAg expression is decreased relative to that in cells maintained at 34 degrees C, there was a dramatic decrease in the N20.1 proliferation rate compared to cells maintained in the absence of neurons at either temperature. This decrease in proliferation was observed within 3 days of co-culture and appeared to precede a further decrease in TAg expression that occurred with time in response to the neurons. In co-cultures the immunoreactivity of N20.1 cells for galactocerebroside increased with time, and the cells appeared to establish contact with neurites and initiate formation of membranous sheets. When the duration of co-culture was extended to 52 days, myelin-like figures were noted by electron microscopy. Thus, the extent of N20.1 differentiation is dependent on the presence of neurons and the duration of co-culture. This culture system represents a potentially powerful tool for the study of neuronal-glial interactions influencing myelinogenesis and remyelination.

Thymic expression of the golli-myelin basic protein gene in the SJL/J mouse

The T cell antigen-specific repertoire is thought to be shaped by thymic expression of self molecules. Since a myelin basic protein (MBP)-like gene (golli-MBP) has been reported to be expressed by cells of the immune system, the present study was undertaken to determine whether the golli-MBP gene was expressed in the mouse thymus and, if so, to characterize transcripts of this gene in this organ. Using exon-specific primers for MBP and golli-MBP, cDNA from thymus and other tissues was amplified, and the amplified products analyzed by Southern blotting with exon-specific oligonucleotide probes. The amplified products were subcloned, and the inserts characterized by DNA sequencing. The thymic transcripts were found to contain golli-MBP exons 1, 2, 3, 5A, 5B, 5C, 6, 7, 8, and 11.