myelin-basic-protein and Tremor

Aspartoacylase (ASPA) catalyzes deacetylation of N-acetylaspartate (NAA) to generate acetate and aspartate. Mutations in the gene for ASPA lead to reduced acetate availability in the CNS during development resulting in the fatal leukodystrophy Canavan disease. Highly specific polyclonal antibodies to ASPA were used to examine CNS expression in adult rats. In white matter, ASPA expression was associated with oligodendrocyte cell bodies, nuclei, and some processes, but showed a dissimilar distribution pattern to myelin basic protein and oligodendrocyte specific protein. Microglia expressed ASPA in all CNS regions examined, as did epiplexus cells of the choroid plexus. Pial and ependymal cells and some endothelial cells were ASPA positive, as were unidentified cellular nuclei throughout the CNS. Astrocytes did not express ASPA in their cytoplasm. In some fiber pathways and nerves, particularly in the brainstem and spinal cord, the axoplasm of many neuronal fibers expressed ASPA, as did some neurons. Acetyl coenzyme A synthase immunoreactivity was also observed in the axoplasm of many of the same fiber pathways and nerves. All ASPA-immunoreactive elements were unstained in brain sections from tremor rats, an ASPA-null mutant. The strong expression of ASPA in oligodendrocyte cell bodies is consistent with a lipogenic role in myelination. Strong ASPA expression in cell nuclei is consistent with a role for NAA-derived acetate in nuclear acetylation reactions, including histone acetylation. Expression of ASPA in microglia may indicate a role in lipid synthesis in these cells, whereas expression in axons suggests that some neurons can both synthesize and catabolize NAA.

Topics: Amidohydrolases; Animals; Astrocytes; Central Nervous System; Disease Models, Animal; Myelin Basic Protein; Rats; Tremor

Transplantation of neural precursor cells has been proposed as a possible approach for replacing missing or damaged central nervous system myelin. Neonatal and adult myelin-deficient shiverer (shi) mice, bearing a mutation of the myelin basic protein (MBP) gene, have been used extensively as hosts for testing cell engraftment, migration, and myelination, but relatively little progress has been made in reversing shi motor deficits. Here we describe a prenatal cell replacement strategy, showing that embryonic stem cells injected into shi blastocyst embryos can generate chimeric mice with strong and widespread immunoreactive MBP expression throughout the brain and a behavioral (motor) phenotype that appears essentially rescued.

Topics: Animals; Ataxia; Basic Helix-Loop-Helix Transcription Factors; Demyelinating Diseases; Embryo, Mammalian; Embryonic Stem Cells; Genotype; Glial Fibrillary Acidic Protein; Mice; Mice, Neurologic Mutants; Mutation; Myelin Basic Protein; Phosphopyruvate Hydratase; Tremor

Fragile X-associated tremor/ataxia syndrome (FXTAS) is a late-onset neurodegenerative disorder caused by premutation expansions (55-200 CGG repeats) in the fragile X mental retardation 1 (FMR1) gene. The pathologic hallmark of FXTAS is the ubiquitin-positive intranuclear inclusion found in neurons and astrocytes in broad distribution throughout the brain. The pathogenesis of FXTAS is likely to involve an RNA toxic gain-of-function mechanism, and the FMR1 mRNA has recently been identified within the inclusions. However, little is known about the proteins that mediate the abnormal cellular response to the expanded CGG repeat allele. As one approach to identify the protein mediators, we have endeavoured to define the protein complement of the inclusion itself. Fluorescence-activated flow-based methods have been developed for the efficient purification of inclusions from the post-mortem brain tissue of FXTAS patients. Mass spectrometric analysis of the entire protein complement of the isolated inclusions, combined with immunohistochemical analysis of both isolated nuclei and tissue sections, has been used to identify inclusion-associated proteins. More than 20 inclusion-associated proteins have been identified on the basis of combined immunohistochemical and mass spectrometric analysis, including a number of neurofilaments and lamin A/C. There is no dominant protein species in the inclusions, and ubiquitinated proteins represent only a minor component; thus, inclusion formation is not likely to reflect a breakdown in proteasomal degradation of nuclear proteins. The list of proteins includes at least two RNA binding proteins, heterogeneous nuclear ribonucleoprotein A2 and muscle blind-like protein 1, which are possible mediators of the RNA gain-of-function in FXTAS.

Topics: Aged; Ataxia; Base Sequence; Blotting, Western; Brain; Brain Chemistry; Chromatography, Liquid; Crystallins; Electrophoresis, Gel, Two-Dimensional; Flow Cytometry; Fluorescent Antibody Technique; Fragile X Syndrome; Heterogeneous-Nuclear Ribonucleoprotein Group A-B; Humans; Intranuclear Inclusion Bodies; Laminin; Male; Molecular Sequence Data; Myelin Basic Protein; Nuclear Proteins; Peptide Mapping; RNA-Binding Proteins; Spectrum Analysis; Tremor; Ubiquitin

Neuronal growth factors are thought to exert a significant degree of control over postnatal oligodendrogenesis, but mechanisms by which these factors coordinateoligodendrocyte development with the maturation of neural networks are poorly characterized. We present here a developmental analysis of aspartoacylase (Aspa)-null tremor rats and show a potential role for this hydrolytic enzyme in the regulation of a postnatal neurotrophic stimulus that impacts on early stages of oligodendrocyte differentiation. Abnormally high levels of brain-derived neurotrophic factor (BDNF) expression in the Aspa-null Tremor brain are associated with dysregulated oligodendrogenesis at a stage in development normally characterized by high levels of Aspa expression. BDNF promotes the survival of proliferating cells during the early stages of oligodendrocyte maturation in vitro, but seems to compromise the ability of these cells to populate the cortex in vivo. Aspartoacylase activity in oligodendrocytes is shown to provide for the negative regulation of BDNF in neurons, thereby determining the availability of a developmental stimulus via a mechanism that links oligodendroglial differentiation with neuronal maturation.

Topics: 2',3'-Cyclic-Nucleotide Phosphodiesterases; Age Factors; Amidohydrolases; Animals; Animals, Genetically Modified; Animals, Newborn; Blotting, Western; Brain; Brain-Derived Neurotrophic Factor; Bromodeoxyuridine; Cell Count; Cell Differentiation; Cell Proliferation; Cells, Cultured; Coculture Techniques; Fluorescent Antibody Technique; Gene Expression; In Situ Hybridization; Myelin Basic Protein; Neurons; Oligodendroglia; Rats; Reverse Transcriptase Polymerase Chain Reaction; RNA, Messenger; Tremor

The cellular/regional expression of myelin-specific proteins: PLP, MBP, CNP-ase, MAG and MOG was investigated in the brains of 14 and 42 days old control and pt-mutant rabbits. The results showed severe reduction in expression of PLP protein, the known molecular target of pt mutation. The minor differences in immunostaining of the other studied myelin-connected proteins between normal and mutant rabbits confirmed once more the deficient and delayed myelination in pt brain. No signs of the increased retention of neither PLP nor any other protein in pt oligodendrocytes were evidenced in this study.

Topics: 2',3'-Cyclic-Nucleotide Phosphodiesterases; Age Factors; Animals; Central Nervous System; Immunohistochemistry; Myelin Basic Protein; Myelin Proteins; Myelin Proteolipid Protein; Myelin Sheath; Myelin-Associated Glycoprotein; Myelin-Oligodendrocyte Glycoprotein; Nerve Tissue Proteins; Rabbits; Tremor

Animals with spontaneous mutations affecting myelin formation have provided useful information about the genetic and cellular mechanisms regulating normal and abnormal myelination. In this paper we describe a novel murine mutation termed hindshaker (hsh), which is inherited in an autosomal recessive manner. Affected mice are characterised by a variable tremor of the hind end which commences at about 2 weeks of age and largely disappears in animals older than 6 weeks. There is hypomyelination affecting predominantly the spinal cord, although the optic nerves and brain are involved to a much lesser degree. The defect of thinly myelinated and naked axons is maximal at 20 days of age and largely resolves with time so that in the adult most axons are myelinated. The myelin structure appears normal and immunostains for the major proteins. Although the distribution of oligodendrocytes in the spinal cord is similar to normal during the period of hypomyelination, there are fewer mature cells. The hsh mutation appears to delay the maturation of oligodendrocytes, particularly in the spinal cord. Additionally, there is a considerable variation in phenotypic expression and in penetrance when the mutation is expressed on different genetic backgrounds, suggesting the hsh locus is subject to the influence of modifying gene(s). Identification of the hsh gene should identify a factor important in the development of oligodendrocytes, particularly those in the spinal cord.

Topics: Animals; Autoradiography; Female; Glial Fibrillary Acidic Protein; Hindlimb; Immunohistochemistry; In Situ Hybridization; Male; Mice; Mice, Inbred C3H; Mice, Neurologic Mutants; Mutation; Myelin Basic Protein; Myelin Proteolipid Protein; Myelin Sheath; Phenotype; RNA, Messenger; Spinal Cord; Spinal Cord Diseases; Tremor

Paralytic tremor (Plp-pt) is a missense mutation of the myelin proteolipid gene (Plp) in rabbits. The myelin yield in the Plp-pt brain is reduced and the protein and lipid composition of central nervous system (CNS) myelin is abnormal. We studied the intracellular transport of the normal and Plp-pt mutant PLP and DM-20 in transiently transfected Cos-7 cells. While the mutant PLP accumulates in the rough endoplasmic reticulum and does not reach the plasma membrane, the spliced isoform of PLP, mutant DM-20, is normally transported to the cell surface and integrated into the membrane. Analysis of rabbit sciatic nerves revealed that concentration of peripheral nervous system (PNS) myelin proteins is normal in Plp-pt myelin. In the PNS like in the CNS, the level of Plp gene products is subnormal. But this does not affect myelination in the PNS where PLP, present in low concentration, is not a structural component of compact myelin. The normal level of Plp gene expression in Schwann cells is low and these results suggest that, in the Plp-pt PNS, Schwann cell function is not affected by the deficiency in PLP and/or the impairment of intracellular PLP transport.

Topics: Animals; Brain Chemistry; Cell Line; DNA, Complementary; Fluorescent Antibody Technique, Indirect; Mutation; Myelin Basic Protein; Myelin Proteolipid Protein; Rabbits; Sciatic Nerve; Transfection; Tremor

To study the effect of SV40 large T-antigen expression in myelin-forming cells of both the central and peripheral nervous system, a series of transgenic mice were generated expressing the SV40 large T-antigen under control of the myelin basic protein (MBP) promoter. Two neurologic phenotypes, designated A and B, appeared among individual transgenic founders and their progeny. The A mice developed a severe action tremor at about 10 days of age that progressed into periods of convulsions and early death by three to four weeks of age. In contrast, the B mice exhibited a progressive hindlimb ataxia and had a more normal lifespan. The A mice displayed hypomyelinating lesions in the central nervous system (CNS), whereas the B mice had lesions in either the peripheral nervous system (PNS) alone or in both the PNS and CNS. Immunohistochemical staining of spinal cord sections of a type A mouse showed a substantial depletion in MBP. Moreover, T-antigen-positive cells appeared predominantly in white matter tracts as randomly distributed single cells. Double labeling immunocytochemistry demonstrated that some of these T-antigen-positive cells were positive for oligodendrocyte differentiation markers MBP and O4. Thus, T-antigen expression appeared to coincide with a terminal stage of oligodendrocyte differentiation.

Topics: Animals; Antigens, Polyomavirus Transforming; Ataxia; Central Nervous System; Cloning, Molecular; Demyelinating Diseases; DNA; Female; Immunohistochemistry; Male; Mice; Mice, Inbred C57BL; Mice, Inbred DBA; Mice, Transgenic; Microscopy, Electron; Myelin Basic Protein; Myelin Sheath; Oligodendroglia; Peripheral Nerves; Phenotype; Promoter Regions, Genetic; Spinal Cord; Tremor

The shiverer mouse mutation has been used as a model in this series of experiments. Germ-line therapy of this disorder has been demonstrated by producing mice transgenic for the wild-type gene for myelin basic protein (MBP). The mutation has also been diagnosed in preimplantation mouse blastocysts.

Topics: Animals; Blastocyst; Female; Genetic Therapy; Mice; Mice, Neurologic Mutants; Mice, Transgenic; Myelin Basic Protein; Optic Nerve; Pregnancy; Prenatal Diagnosis; Tremor

We report a mother and son with a deletion at 18q22.3. Both have the typical manifestations of the 18q- syndrome. In addition, both have an action tremor which became apparent in childhood. The mother subsequently developed chorea and dysmetria in late adolescence. Magnetic resonance imaging of their brains showed poor myelination of the central white matter tracts with relatively normal myelination of the corpus callosum. We propose that these neurologic findings are most likely due to a failure of expression of the myelin basic protein gene.

Topics: Abnormalities, Multiple; Adult; Brain; Chromosome Deletion; Chromosomes, Human, Pair 18; Ear; Female; Humans; Infant; Magnetic Resonance Imaging; Male; Myelin Basic Protein; Tremor