Developmental expression of P0 mRNA and P0 protein in the sciatic nerve and the spinal nerve roots of the rat

Expression of myelin P0 protein by myelinating Schwann cells in vivo is dependent on axonal influences. This report describes P0 gene expression during development of rat sciatic nerve and spinal nerve roots using Northern blotting, in situ hybridization and immunohistochemistry. We demonstrate that: (1) the appearance of P0 mRNA and P0 protein in Schwann cells during nerve development in the rat begins prenatally, at day 18 post-fertilization (E18); (2) P0 mRNA and P0 protein have essentially identical developmental profiles, and are expressed in Schwann cells that are many days prior to myelin formation; (3) initial P0 gene expression is greatest in Schwann cells at the periphery of nerve bundles and in Schwann cells in contact with motor axons; (4) the decline in P0 expression with nerve maturation is accompanied by a sharp decline in P0 message levels in most Schwann cells, but a small subpopulation of these cells continue to synthesize very high levels of P0 mRNA. This study provides data on myelin P0 protein gene expression and distribution during PNS development and adds further insights into the axonal influences controlling Schwann cell behaviour during myelination of the rat PNS.

Analysis of the human MBP promoter in primary cultures of oligodendrocytes: positive and negative cis-acting elements in the proximal MBP promoter mediate oligodendrocyte-specific expression of MBP

Since the regulation of myelin basic protein expression depends primarily on the initiation of transcription, we analyzed the 5' flanking region of the human myelin basic protein gene in transient transfection studies in primary cultures of developing oligodendrocytes. We demonstrated that 149 base pairs 5' of the initiation of transcription was sufficient to direct oligodendrocyte-specific expression of myelin basic protein. The capsite of the fusion transcript was identical with that of the endogenous myelin basic protein transcript, and chloramphenicol acetyl transferase reporter gene expression was restricted to oligodendrocytes in these cultures. Within this 149 base pair region, one distal, negative cis-acting segment, containing a consensus nuclear factor I site, and one proximal, positive cis-acting segment were identified. The distal segment behaved more negatively in Cos-7 cells than in oligodendrocytes, reducing expression to background levels. Furthermore, these functionally important cis-acting segments bound oligodendrocyte nuclear proteins in a pattern differing from other cells, including Cos-7 cells. Interestingly, the distal segment increased heterologous SV40 promoter activity in oligodendrocytes but had no effect on the SV40 promoter in Cos-7 cells. We conclude that the functionally negative distal segment may mediate oligodendrocyte-specific expression of MBP by restricting its expression in other cells. These experiments strongly support using primary cultures of oligodendrocytes for analyzing the myelin-specific promoters.

Axons modulate the expression of transforming growth factor-betas in Schwann cells

We have investigated the expression of transforming growth factor (TGF)-beta 1,-beta 2, and -beta 3 in developing, degenerating, and regenerating rat peripheral nerve by immunohistochemistry and Northern blot analysis. In normal adult sciatic nerve, TGF-beta 1, -beta 2, and -beta 3 are detected in the cytoplasm of Schwann cells, and the levels of TGF-beta 1 and -beta 3 mRNAs are constant during post-natal development. When sciatic nerves are transected to cause axonal degeneration and prevent axonal regeneration, the level of TGF-beta 1 mRNA in the distal nerve-stump increases markedly and remains elevated, whereas the level of TGF-beta 3 mRNA falls modestly and remains depressed. When sciatic nerves are crushed to cause axonal degeneration and allow axonal regeneration, the level of TGF-beta 1 mRNA initially increases as axons degenerate, and then falls as axons regenerate. TGF-beta 2 mRNA was not detected in developing or lesioned sciatic nerves at any time. Cultured Schwann cells have high levels of TGF-beta 1 mRNA, the amount of which is reduced by forskolin, which mimics the effect of axonal contact. These data demonstrate that Schwann cells express TGF-beta 1, -beta 2, and -beta 3, and that TGF-beta 1 and -beta 3 mRNA predominate over TGF-beta 2 mRNA in peripheral nerve. Axonal contact and forskolin decrease the expression of TGF-beta 1 in Schwann cells.

Appearance of PLP mRNA in specific regions of the developing rat lumbosacral spinal cord as revealed by in situ hybridization

The capacity of specific regions and fiber tracts of developing rat lumbosacral spinal cord to express proteolipid protein (PLP) mRNA was examined using in situ hybridization. PLP mRNA was undetectable at Day 18 postfertilization but present in the white matter by Postnatal Day 0 (P0). Initially, levels of PLP mRNA were higher in ventral than in dorsal funiculi. Hybridization signal was observed in the corticospinal tract by P10. Appearance of PLP message in gray matter lagged several days behind that in white matter. The expression of PLP mRNA in gray matter rose between P10 and P40 and the abundance of PLP transcript remained high in white matter during the same period. In the adult spinal cord some oligodendrocytes in the Lissauer tract and in the posterior commissure expressed low levels of PLP mRNA, which was undetectable in the substantia gelatinosa. Comparing the time of emergence of PLP mRNA to the histological appearance of myelination gave evidence that the message is expressed in oligodendrocytes that are not many days away from myelin formation. These results provide new information on the topographic distribution of PLP mRNA during myelination of the rat spinal cord.

Oligodendrocyte maturation and myelin gene expression in PDGF-treated cultures from rat cerebral white matter

Myelination in the CNS is accompanied by the differentiation of oligodendrocytes as well as the coordinate expression of a group of myelin-specific genes, including those encoding proteolipid protein and myelin basic protein. In order to compare the timing of the onset of myelin gene expression with the known sequence of oligodendrocyte maturation, we analyzed cerebral white matter cultures grown in the presence of platelet-derived growth factor for expression of the mRNAs encoding these myelin proteins, as well as for the numbers of oligodendrocytes and their precursors. Platelet-derived growth factor treatment increased the rate of oligodendrocyte precursor cell proliferation and the number of mature oligodendrocytes. Platelet-derived growth factor also produced a significant increase in oligodendrocyte precursors prior to an increase in their proliferation rate, suggesting that platelet-derived growth factor may also have an effect on oligodendrocyte precursor survival. Furthermore, steady-state levels of proteolipid protein and myelin basic protein mRNAs increased within 24 of the addition of platelet-derived growth factor, before any significant change in the numbers of oligodendrocytes or their precursors, demonstrating that platelet-derived growth factor also regulates myelin gene expression. At later times after platelet-derived growth factor addition, however, when the number of oligodendrocytes and their precursors was rapidly increasing, the increase in proteolipid protein and myelin basic protein mRNA levels was proportionally much greater than the increase in oligodendroglial lineage cells, suggesting that platelet-derived growth factor also increased the number of proteolipid protein and myelin basic protein transcripts per cell; this interpretation was confirmed by in situ hybridization analysis. Finally, by examining the co-expression of galactocerebroside using the epitopes recognized by the Ranscht monoclonal antibody and proteolipid protein mRNA in individual cells by a combination of in situ hybridization and immunohistochemistry, we demonstrated that oligodendrocytes express proteolipid protein and myelin basic protein mRNA. Oligodendrocyte maturation, as measured by surface galactocerebroside expression, is thus contemporaneous with the activation of myelin-specific gene expression.

Molecular analysis of the 18q- syndrome--and correlation with phenotype

Seven individuals with deletions of the distal long arm of chromosome 18 were evaluated at the clinical, cytogenetic, and molecular levels. The patients had varying degrees of typical clinical findings associated with the 18q- syndrome. Cytogenetic analysis revealed deletions from 18q21.3 or 18q22.2 to qter. Somatic cell hybrids derived from the patients were molecularly characterized using ordered groups of probes isolated from a chromosome 18-specific library. In general, the size of the deletion could be correlated with the severity of the phenotype. Based on the clinical pictures of these seven patients, a preliminary phenotypic map for the clinical features associated with deletions of the distal portion of the long arm has been generated. Furthermore, genes previously localized to 18q21 were mapped relative to the chromosome breakpoints present in these patients.

Mitogen-expanded Schwann cells retain the capacity to myelinate regenerating axons after transplantation into rat sciatic nerve

We have developed a method for genetically modifying Schwann cells (SCs) in vitro and then assessed whether these SCs could interact normally with axons in vivo. Rat SCs were transduced in vitro with the lacZ gene by using a retroviral vector and then expanded with the SC mitogens forskolin and glial growth factor. These mitogen-expanded SCs had an abnormal phenotype as compared to both SCs in vivo and primary SCs in vitro, yet when they were introduced into a regenerating rat sciatic nerve, they formed morphologically normal myelin sheaths around the axons. These results demonstrate that SCs can be genetically altered, their numbers expanded in culture, and yet respond appropriately to axonal signals in the peripheral nervous system. This approach offers a plausible way to manipulate genes involved in axon-SC interactions, including genes that may be defective in some inherited peripheral neuropathies.

Axons modulate the expression of proteolipid protein in the CNS

We examined the expression of mRNA encoding proteolipid protein (PLP), the major myelin protein in the CNS, in developing rat cerebrum, and in normal and degenerating optic nerves. PLP transcripts were initiated at two clusters of start sites that were separated by about 30 base pairs. During the peak of PLP mRNA expression in developing cerebrum, a higher proportion of PLP transcripts were initiated from the distal start site, furthest from the open reading frame, than in mature cerebrum. We enucleated one eye of immature rats to cause Wallerian degeneration in the optic nerve. In these degenerating optic nerves, the steady state levels of PLP mRNA fell markedly, and the proportion of distally initiated PLP transcripts declined to the same proportion found in normal adult nerves. Changes in myelin gene expression were not limited to PLP mRNA, as the steady-state levels of myelin basic protein (MBP) mRNA paralleled those of PLP mRNA in the developing cerebrum and in degenerating optic nerves. Thus, oligodendrocytes require axons to maintain their normal levels of PLP and MBP transcripts and the high proportion of distally initiated PLP transcripts that characterize early myelination.

Structure and expression of proteolipid protein in the peripheral nervous system

Proteolipid protein (PLP), the major myelin protein in the central nervous system (CNS), is also made by Schwann cells (SC) in the peripheral nervous system (PNS) but is not incorporated into the SC myelin sheath. We analyzed several PLP cDNA clones isolated from a rat sciatic nerve cDNA library and found that their coding sequences were identical to PLP cDNAs previously isolated from the CNS. In addition, we have discovered an unusual form of PLP message, present in both brain and sciatic nerve RNA, that is likely formed by alternative splicing within the 3' untranslated region of the primary PLP transcript. The absence of PLP from the SC myelin sheath thus cannot be explained by an alteration in its amino acid sequence. Steady-state levels of PLP mRNA in SC cultures treated with the cAMP analogue dibutyryl cAMP (dBcAMP) were not increased, whereas dBcAMP increased steady-state levels of mRNA encoding the major myelin protein, P0. We have also shown that expression of PLP, unlike that of P0, is regulated in SC in vitro at a posttranscriptional level. Finally, the steady-state levels of P0 mRNA are much more dramatically reduced than those of PLP mRNA during Wallerian degeneration of the peripheral nerve. Thus PLP expression in the PNS is probably controlled by different molecular mechanisms from P0, and may not be part of the coordinate program of myelin gene expression. In contrast to its expression in the PNS, transcription of PLP in the CNS is coordinately regulated along with the other myelin protein genes, suggesting there may be differences in the cis-acting elements and transacting factors involved in the regulation of PLP transcription in SC and oligodendrocytes (OC). Consistent with this notion, we have found that most PLP transcripts are initiated at the more proximal of two start sites in the PNS, while in the CNS proportionally more PLP transcripts are initiated from the distal start site. We propose that the proximal site, utilized predominantly in SC, is responsible for maintenance expression of PLP and is not inducible, while the distal site is responsible for the rapid, inducible increase of PLP message during brain development.

Oculodentodigital dysplasia syndrome associated with abnormal cerebral white matter

Oculodentodigital dysplasia (ODDD) syndrome is an uncommon inherited disorder with eye and facial abnormalities, syndactyly, and defects in tooth enamel. Some of the previously reported patients with ODDD syndrome also manifested spastic quadriparesis. We describe a patient with sporadic ODDD syndrome referred for evaluation of progressive spastic paraparesis. Magnetic resonance imaging of the brain demonstrated abnormal white matter, which suggests an explanation for the observed spastic paraparesis.

Segmental spinal muscular atrophy and dermatological findings in a patient with chromosome 18q deletion

We have evaluated a young woman with segmental spinal muscular atrophy, who has a deletion of a portion of the long arm of chromosome 18. She also has vitiligo and lichen sclerosis et atrophicus. She has neither the facial dysmorphism nor the mental deficit usually associated with the 18q- syndrome. Magnetic resonance imaging scan of her brain demonstrates high signal intensity consistent with abnormal myelination. Southern blot analysis of her DNA demonstrates that the deletion includes the gene for human myelin basic protein. Neither spinal muscular atrophy nor this patient's skin manifestations have been previously reported in association with 18q-.

DM-GRASP, a novel immunoglobulin superfamily axonal surface protein that supports neurite extension

We have identified a 95 kd cell surface protein, DM-GRASP, that is expressed on a restricted population of axons. Its expression begins early in chick embryogenesis, and within the spinal cord it is localized to axons in the dorsal funiculus, midline floorplate cells, and motoneurons. Antibodies to DM-GRASP impair neurite extension on axons, and purified DM-GRASP supports neurite extension from chick sensory neurons. We have cloned and sequenced the cDNA corresponding to this protein and find that it is a new member of the immunoglobulin superfamily of adhesion molecules. Consequently we have named this protein DM-GRASP, since it is an immunoglobulin-like restricted axonal surface protein that is expressed in the dorsal funiculus and ventral midline of the chick spinal cord.

Complicated hereditary spastic paraparesis with cerebral white matter lesions

A family is described with 5 males in a single generation affected with a previously undescribed complicated form of hereditary spastic paraparesis (HSP). The disease is characterized by speech difficulties, lower limb spasticity and hyper-reflexia, mental retardation, cerebellar ataxia, and tremor. The disease starts in the first decade of life and progresses for 3 to 6 years before stabilizing. Magnetic resonance imaging (MRI) of the brain demonstrates bilateral posterior periventricular white matter lesions. Visual evoked responses are markedly prolonged, but electromyography (EMG) and nerve conduction velocity studies are normal. Three of the 4 living affected members of this pedigree exhibit red-green color vision defects. The presentation of a new complicated hereditary spastic paraparesis syndrome in this pedigree extends our understanding of the variability and heterogenity of this syndrome and suggests an approach for the evaluation of similar families in future genetic studies.

Neuronal modulation of Schwann cell glial fibrillary acidic protein (GFAP)

Adult rat sciatic nerves contain cytoskeletal peptides that resemble CNS glial fibrillary acidic protein (GFAP) in immunoreactivity and molecular weight. Immunohistological examination of teased nerve fascicles indicated that these peptides are expressed selectively by Schwann cells related to small axons. Radiolabelled mouse and rat CNS GFAP cDNA probes hybridized with a single, 2.7 kb RNA band in Northern blots prepared from total RNA from both rat sciatic nerve and rat brain. Sciatic nerve GFAP mRNA was detectable by this means in adult, 2 month, or 21 day postnatal rats, but not in 3,6, or 10 day postnatal rats. Sciatic nerve transection caused a marked reduction in the level of GFAP mRNA in the axotomized distal stump. We conclude that Schwann cell synthesis of GFAP is developmentally regulated and that Schwann cells, unlike astroglia, require continued trophic input from small axons in order to express GFAP.

Nucleotide sequence analysis of the purEK operon encoding 5'-phosphoribosyl-5-aminoimidazole carboxylase of Escherichia coli K-12

5'-Phosphoribosyl-5-aminoimidazole (AIR) carboxylase (EC 4.1.1.21) catalyzes step 6, the carboxylation of AIR to 5'-phosphoribosyl-5-aminoimidazole-4-carboxylic acid, in the de novo biosynthesis of purine nucleotides. As deduced from the DNA sequence of restriction fragments encoding AIR carboxylase and supported by maxicell analyses, AIR carboxylase was found to be composed of two nonidentical subunits. In agreement with established complementation data, the catalytic subunit (deduced Mr, 17,782) was encoded by the purE gene, while the CO2-binding subunit (deduced Mr, 39,385) was encoded by the purK gene. These two genes formed an operon in which the termination codon of the purE gene overlapped the initiation codon of the purK gene. The 5' end of the purEK mRNA was determined by mung bean nuclease mapping and was located 41 nucleotides upstream of the proposed initiation codon. The purEK operon is regulated by the purR gene product, and a purR regulatory-protein-binding site related to the sequences found in other pur loci was identified in the purEK operon control region.

Organization and expression of the human myelin basic protein gene

The human brain contains four isoforms of myelin basic protein (MBP), previously identified by cDNA cloning. We have now isolated and characterized genomic clones encoding the human MBP gene. The gene is 45 kb in extent and consists of seven exons. Alternative splicing of the primary MBP transcript can account for all four human MBP isoforms. The intron-exon boundaries of the gene have also been determined, and all conform to the known consensus splice sequences. These sequences, however, do not explain the alternative splicing pattern found in human brain. Transcription of the human MBP gene begins at a single site within the MBP promoter, and all four MBP isoforms are transcribed from this same site. The promoter region does not contain any known sequence elements, but does have a 12-bp sequence also found in the JC virus 98-bp tandem repeat. A relative gradient of MBP transcription is found from caudal to rostral within the developing human brain, which parallels the known sequence of myelination found in these areas. RNase protection of brain RNA demonstrates more of the 21.5-kD and 20.5-kD MBP mRNAs in neonatal brain than in the adult frontal cortex, which suggests that alternative splicing of the primary MBP transcript is also regulated temporally during myelin development. These data show that regulation of myelination is complex, involving regional cellular interactions and trans activation of transcription, as well as modulation of alternative splicing. Comparison of the human and mouse data also suggests that alternative splicing plays an important role in myelin biogenesis.

Human gamma enolase: isolation of a cDNA clone and expression in normal and tumor tissues of human origin

We have isolated and sequenced a cDNA clone encoding the human gamma enolase. Comparison of our cDNA sequence and the rat gamma enolase sequence revealed 97% homology at the level of amino acid sequence. The two coding regions were 91% homologous on the nucleotide level, whereas the 3' noncoding regions were much less homologous (32%). Further comparison of our cDNA sequence with the human alpha enolase revealed an 82% homology at the amino acid level and a 75% homology at the nucleotide level for the two coding regions, whereas the 3' nontranslated regions were only 30% homologous. Using a portion of the 3' nontranslated region of our cDNA, shown to be specific for human gamma enolase, a single 2.5 kb mRNA was detected in human brain tissue. This same gamma enolase message was also found in a number of human normal nonneuronal tissues, and in several human tumor-derived cell lines. Expression of the mRNA for the gamma enolase subunit should thus be used with caution when identifying the cells of neuronal or neuroendocrine origin.

Human cDNA clones for an alpha subunit of Gi signal-transduction protein

Two cDNA clones were obtained from a lambda gt11 cDNA human brain library that correspond to alpha i subunits of G signal-transduction proteins (where alpha i subunits refer to the alpha subunits of G proteins that inhibit adenylate cyclase). The nucleotide sequence of human brain alpha i is highly homologous to that of bovine brain alpha i [Nukada, T., Tanabe, T., Takahashi, H., Noda, M., Haga, K., Haga, T., Ichiyama, A., Kangawa, K., Hiranaga, M., Matsuo, H. & Numa, S. (1986) FEBS Lett. 197, 305-310] and the predicted amino acid sequences are identical. However, human and bovine brain alpha i cDNAs differ significantly from alpha i cDNAs from human monocytes, rat glioma, and mouse macrophages in amino acid (88% homology) and nucleotide (71-75% homology) sequences. In addition, the nucleotide sequences of the 3' untranslated regions of human and bovine brain alpha i cDNAs differ markedly from the sequences of human monocyte, rat glioma, and mouse macrophage alpha i cDNAs. These results suggest there are at least two classes of alpha i mRNA.

The human myelin-basic-protein gene: chromosomal localization and RFLP analysis

With a human myelin-basic-protein (MBP) cDNA used as a probe, the human MBP gene has been mapped to chromosome region 18q22-q23 by a combination of Southern hybridization to a panel of somatic-cell hybrid DNAs and in situ hybridization to metaphase chromosomes. Restriction-fragment-length polymorphisms (RFLPs) have also been identified with this probe in human DNA, by means of the restriction enzymes BamHI, PvuII, and PstI. In studies of informative families, the alleles of the BamHI and PvuII polymorphisms have been shown to segregate as Mendelian traits.

Human cDNA clones for four species of G alpha s signal transduction protein

lambda gt11 cDNA libraries derived from human brain were screened with oligonucleotide probes for recombinants that code for alpha subunits of G signal transduction proteins. Eleven alpha s clones were detected with both probes and characterized. Four types of alpha s cDNA were cloned that differ in nucleotide sequence in the region that corresponds to amino acid residues 71-88. The clones differ in the codon for alpha s amino acid residue 71 (glutamic acid or aspartic acid), the presence or absence of codons for the next 15 amino acid residues, and the presence or absence of an adjacent serine residue. S1 nuclease protection experiments revealed at least two forms of alpha s mRNA. A mechanism for generating four species of alpha s mRNA by alternative splicing of precursor RNA is proposed.

Identification of three forms of human myelin basic protein by cDNA cloning

We have isolated cDNA clones encoding three separate forms of human myelin basic protein (MBP), 21.5, 18.5, and 17.2 kDa, and have determined the nucleotide sequence of each. The three forms share a common sequence but differ by the inclusion of a 26-residue amino acid sequence near the N terminus of the 21.5-kDa protein or by the absence of an 11-residue amino acid sequence near the C terminus of the 17.2-kDa protein. The sequences either added to or deleted from the major 18.5-kDa MBP correspond exactly to exons 2 and 5 of the mouse MBP gene, suggesting that the human and mouse genes have similar exon structures. We have also identified the 21.5-kDa human MBP on immunoblots using antisera raised to a peptide encoded by the mouse exon 2 sequence. Southern blotting studies of human genomic DNA reveal a simple pattern consistent with a single human MBP gene. Thus, the three MBP mRNAs are likely to arise from alternative splicing of a primary human MBP transcript. Conservation of the 26 amino acid mouse exon 2 sequence in human MBP suggests an important role for this sequence in myelination.

Molecular cloning and characterization of the purE operon of Escherichia coli

The purE operon of Escherichia coli has been cloned and localized to a 1.7-kb HpaI fragment. The operon has been further characterized by subcloning into the lac fusion vector, pMC1403, and by the construction of BAL 31-generated deletions. The purE regulation region has been identified by assay of beta-galactosidase produced by pur-lac fusion plasmids and by RNA polymerase binding to end-labelled restriction fragments. Two purE promoters have been identified; one strong that is regulated by purines, the other weaker which is not regulated. The latter may be internal to the purE1 structural gene.

Alternative splicing accounts for the four forms of myelin basic protein

We have isolated cDNA clones encoding the four different forms of mouse myelin basic protein (MBP) and have analyzed the structure of the MBP gene. The three larger forms of MBP differ from the smallest by the inclusion of either or both of two short amino acid sequences at positions 57 and 124 of the smallest protein. The mouse genome contains a single MBP gene comprised of seven exons. The two amino acid sequences present only in the larger MBPs are encoded by separate exons. Furthermore, all exons in the coding region begin or end in complete codons so that alternative splicing does not alter the reading frame. We conclude that the four forms of this myelin protein are encoded in separate mRNAs, each derived by a simple alternative splicing of the primary MBP gene transcript. Comparison of the amino acid sequence encoded by each exon with a recent model of the secondary structure of MBP suggests that each of the seven exons encodes one or two of the predicted structural motifs of the protein.

Chickenpox with delayed contralateral hemiparesis caused by cerebral angiitis

Chickenpox and herpes zoster ophthalmicus are caused by the same virus. Herpes zoster ophthalmicus can be followed by contralateral hemiparesis, which is thought to be caused by spread of varicella-zoster virus to blood vessels contiguous to the trigeminal nerve and its branches. We report what we believe to be the first case of a patient with chickenpox followed by hemiparesis in whom there was angiographic evidence of an associated vasculitis similar to that found with herpes zoster ophthalmicus.