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K A Nave

Publications and source records attributed to K A Nave.

53 records · Page 3Linked to original sources
PubMed1994

Neurological mouse mutants and the genes of myelin.

The prospect to create mouse mutants of virtually any cloned gene has renewed interest in the genetic analysis of mammalian brain development. A diverse group of spontaneous and engineered mouse mutants, characterized by a defect of myelin formation, has been intensively studied from the morphological to the molecular level. In this system, genetics has been successfully applied to analyze a corresponding set of membrane proteins which help to elaborate a defined structural entity, compact myelin. Shiverer, jimpy, Trembler, and protein zero (P0)-deficient mice demonstrate the overall function of myelination and have become models for human neurological diseases. They also illustrate some of the problems encountered in defining protein functions from complex mutant phenotypes.

Animals↗
PubMed1994

Premature arrest of myelin formation in transgenic mice with increased proteolipid protein gene dosage.

Proteolipid protein (PLP) is an integral membrane protein of CNS myelin. Mutations of the X chromosome-linked PLP gene cause glial cell death and myelin deficiency in jimpy mice and other neurological mutants. As part of an attempt to rescue these mutants by transgenic complementation, we generated normal mouse lines expressing autosomal copies of the entire wild-type PLP gene. Surprisingly, increase of the PLP gene dosage in nonmutant mice with only 2-fold transcriptional overexpression results in a novel phenotype characterized by severe hypomyelination and astrocytosis, seizures, and premature death. This demonstrates that precise control of the PLP gene is a critical determinant of terminal oligodendrocyte differentiation. Dysmyelination of PLP transgenic mice provides experimental evidence that Pelizaeus-Merzbacher disease, previously associated with a partial duplication of the human X chromosome, can be caused by doubling of the PLP gene dosage.

Animals↗
PubMed1994

Mice deficient for the myelin-associated glycoprotein show subtle abnormalities in myelin.

Using homologous recombination in embryonic stem cells, we have generated mice with a null mutation in the gene encoding the myelin-associated glycoprotein (MAG), a recognition molecule implicated in myelin formation. MAG-deficient mice appeared normal in motor coordination and spatial learning tasks. Normal myelin structure and nerve conduction in the PNS, with N-CAM overexpression at sites normally expressing MAG, suggested compensatory mechanisms. In the CNS, the onset of myelination was delayed, and subtle morphological abnormalities were detected in that the content of oligodendrocyte cytoplasm at the inner aspect of most myelin sheaths was reduced and that some axons were surrounded by two or more myelin sheaths. These observations suggest that MAG participates in the formation of the periaxonal cytoplasmic collar of oligodendrocytes and in the recognition between oligodendrocyte processes and axons.

Animals↗
PubMed1994

NEX-1: a novel brain-specific helix-loop-helix protein with autoregulation and sustained expression in mature cortical neurons.

Mutations affecting peripheral nervous system development in Drosophila and mouse indicate that neural differentiation depends on the coordinated expression of cell type-specific bHLH proteins. We have identified a novel bHLH gene, termed NEX-1, which is expressed exclusively and abundantly in the mammalian central nervous system. By in situ hybridization, induction of the rodent NEX-1 gene coincides with the generation of postmitotic neurons and parallels overt neuronal differentiation and synaptogenesis. Unexpected for bHLH proteins, NEX-1 may play a role in neuronal function throughout adult life. High levels of its mRNA are sustained in mature pyramidal neurons of the hippocampus, cerebellum and several neocortical areas previously associated with learning and memory formation. When ectopically expressed in PC12 cells, NEX-1 transactivates the promoter of its own gene. This suggests that positive autoregulation stabilizes the activity of NEX-1 and its target genes in subsets of mature neurons.

Amino Acid Sequence↗
PubMed1994

The maedi-visna virus Tat protein induces multiorgan lymphoid hyperplasia in transgenic mice.

Sheep infected with maedi-visna virus experience immunological disorders leading to progressive chronic diseases involving the brain, lung, spleen, and lymph nodes. To study the biological activity of the viral transactivating Tat protein, we generated transgenic mice carrying the tat gene. Analysis of the transgenic mouse tissues for tat mRNA revealed that while low at the messenger level, the expression of the transgene correlated with dramatic follicular lymphoproliferative disorders involving the lung, spleen, lymph nodes, and skin. This finding suggests that the viral protein possesses a high pathological potency. Our findings show that the maedi-visna virus tat gene product contributes to the pathogenesis of multiorgan proliferative disorders associated with maedi-visna virus infection.

Animals↗
PubMed1993

Oligodendrocyte development and differentiation in the rumpshaker mutation.

The jimpy rumpshaker (jprsh) mutation is an amino acid substitution in exon 4 (Ile186-->Thr) of the proteolipid protein (PLP) gene on the X chromosome. Affected mice show moderate hypomyelination of the central nervous system (CNS) with increased numbers of oligodendrocytes in the white matter of the spinal cord, a feature distinguishing them from other PLP mutations such as jp, in which premature cell death occurs with reduced numbers of oligodendrocytes. Myelin sheaths of jprsh immunostain for myelin basic protein (MBP) and DM-20, but very few contain PLP. This study examines the differentiation of oligodendrocytes cultured from the spinal cords of young mutant and wild type mice using various surface and cytoplasmic antigenic markers to define the stage of development. The majority of oligodendrocytes from mutant mice progress normally to express MBP; approximately 30%, relative to wild type, contain DM-20 at the in vivo age of 16 days, but very few immunostain for PLP or the O10 and O11 markers. The morphology of mutant cells in respect to membrane sheets and processes appears similar to normal. The jprsh oligodendrocyte is, therefore, characterized by a failure to express the markers indicative of the most mature cell; however, it is probably able to achieve a normal period of survival. These data, taken in conjunction with previous results, suggest that the PLP gene has at least two functions; one, probably involving PLP, is concerned with a structural role in normal myelin compaction; the other, perhaps related to DM-20 (or another lower molecular weight proteolipid), is essential for cell survival. The mutation in jprsh at residue 186 suggests that this region, which is common to PLP and DM-20, is not critical for this latter function.

Animals↗
PubMed1992

Uncoupling of hypomyelination and glial cell death by a mutation in the proteolipid protein gene.

Proteolipid protein (PLP; M(r) 30,000) is a highly conserved major polytopic membrane protein in myelin but its cellular function remains obscure. Neurological mutant mice can often provide model systems for human genetic disorders. Mutations of the X-chromosome-linked PLP gene are lethal, identified first in the jimpy mouse and subsequently in patients with Pelizaeus-Merzbacher disease. The unexplained phenotype of these mutations includes degeneration and premature cell death of oligodendrocytes with associated hypomyelination. Here we show that a new mouse mutant rumpshaker is defined by the amino-acid substitution Ile-to-Thr at residue 186 in a membrane-embedded domain of PLP. Surprisingly, rumpshaker mice, although myelin-deficient, have normal longevity and a full complement of morphologically normal oligodendrocytes. Hypomyelination can thus be genetically separated from the PLP-dependent oligodendrocyte degeneration. We suggest that PLP has a vital function in glial cell development, distinct from its later role in myelin assembly, and that this dichotomy of action may explain the clinical spectrum of Pelizaeus-Merzbacher disease.

Amino Acid Sequence↗
PubMed1991

Induction of the myelin proteolipid protein (PLP) gene in C6 glioblastoma cells: functional analysis of the PLP promotor.

The terminal differentiation of postmitotic oligodendrocytes is marked by the induction of myelin-specific genes. In this report, we demonstrate that culture conditions that induce oligodendrocyte differentiation of glial progenitor cells also induce differentiation of C6 glioblastoma cells, as monitored by activated transcription of the gene encoding proteolipid protein (PLP), the major myelin protein of the CNS. When assayed by transfections of hybrid reporter plasmids, the transcriptional control region of the PLP gene is preferentially active in differentiated C6 cells and contains both positive and negative cis-regulatory elements. In general, functional identification of these elements is well correlated with the binding sites of glial nuclear proteins, as visualized by the presence of DNase I-protected footprints. A sequence within one positive cis-regulatory element of the PLP gene is conserved in the control regions of three other myelin-specific genes, suggesting that their coordinate transcription may involve a common regulatory mechanism.

Animals↗
PubMed1989

Proteolipid proteins: structure and genetic expression in normal and myelin-deficient mutant mice.

Myelin, the unique product of a glial cell membrane that electrically insulates the nerve axon, is composed of relatively few major protein components. The recent characterization of these proteins by molecular cloning techniques has raised interest in studies of myelin formation at the molecular level. Proteolipids, a family of integral membrane proteins specific to myelin of the central nervous system, are highly abundant and serve a structural function in the architecture of the multilayered sheath. A critical role for proteolipid protein (PLP) expression during normal development and for the survival of the myelinating oligodendrocyte is reflected in severe developmental disorders of mice that result from genetic mutations in the single structural gene for PLP. The analysis of PLP gene expression in these mutants and other dysmyelinating mouse strains has revealed interactions between myelin-specific genes that may underlie the coordinate development of oligodendrocytes and myelination in the brain.

Animals↗
PubMed1987

Two forms of 1B236/myelin-associated glycoprotein, a cell adhesion molecule for postnatal neural development, are produced by alternative splicing.

The structures of two rat brain-specific 1B236 mRNAs, alternative splice products from a single gene regulated differently during postnatal brain development, were deduced from full-length cDNA clones. The 626- and 582-amino acid-long encoded proteins are indistinguishable from two forms of myelin-associated glycoprotein, a cell adhesion molecule involved in axonal-glial and glial-glial interactions in postnatal brain development, particularly in myelination. The two proteins share a single membrane-spanning domain and a glycosylated N terminus but differ in the structures of their C termini. The N terminus consists of five domains related in sequence to each other and to immunoglobulin-like molecules, especially the neural cell adhesion molecule N-CAM, suggesting a common structure for cell adhesion molecules.

Aging↗
PubMed1987

Splice site selection in the proteolipid protein (PLP) gene transcript and primary structure of the DM-20 protein of central nervous system myelin.

Proteolipid protein (PLP) is the major myelin membrane protein of the central nervous system. We have isolated a copy of an alternatively spliced PLP gene transcript from a mouse brain cDNA library that was screened for PLP-related sequences. The encoded 241-amino acid protein differs from PLP by an internal deletion of 35-amino acid residues (116-150) from the major hydrophilic domain. This PLP variant is identical with the DM-20 protein of myelin, previously described as a brain-specific myelin component and known to be related to PLP. We determined the corresponding nucleotide sequence of the rat PLP gene and found that DM-20 mRNA results when a second 5' splice site, located 105 nucleotides within the third exon of the primary PLP transcript, is utilized in precursor mRNA (pre-mRNA) splicing. This demonstrates that alternative 5' splice site selection can determine the protein product of a cellular gene. DM-20 mRNA is expressed in rat brain with approximately 50% abundance relative to PLP mRNA and appears to be developmentally coregulated.

Amino Acid Sequence↗
PubMed1987

A single nucleotide difference in the gene for myelin proteolipid protein defines the jimpy mutation in mouse.

We have previously shown that, in the myelin-deficient jimpy mutant mouse, 74 nucleotides are absent from the mRNA for proteolipid protein (PLP) as a result of aberrant RNA processing. To define the exact site of the jimpy mutation, we have analyzed the PLP gene obtained from a jimpy mouse genomic library. We find that the nucleotide sequence that is absent from jimpy PLP mRNA is fully preserved in the jimpy PLP gene. The missing segment corresponds to a separate exon, equivalent to exon 5 of the human PLP gene. The nucleotide sequence at the 3' end of intron 4 in the jimpy PLP gene contains a single point mutation. A base change A----G in the 3' acceptor splice site has altered a position that is 100% conserved in all published splice acceptor sequences. We conclude that the primary genetic defect of the jimpy mouse is a single base change in the PLP gene disabling an invariant recognition sequence of RNA splicing.

Animals↗
PubMed1986

Jimpy mutant mouse: a 74-base deletion in the mRNA for myelin proteolipid protein and evidence for a primary defect in RNA splicing.

The mouse mutant jimpy carries an X chromosome-linked recessive gene defect that affects the formation of myelin in the central nervous system. To understand the molecular basis of the jimpy mutation, we have examined the expression of mRNAs encoding myelin proteolipid protein (PLP). PLP mRNAs were detectable in jimpy brain RNA at 21 days after birth but were severely reduced in abundance compared to wild-type littermates. Nucleotide sequence analysis of cDNA clones for PLP mRNA, isolated from a cDNA library of jimpy brain poly(A)+ RNA, revealed that the PLP mRNA expressed in jimpy contained a deletion of 74 nucleotides with respect to the wild-type sequence. This deletion causes a frameshift in the open reading frame resulting in an altered carboxyl terminus for jimpy PLP. Probes specific for the deleted sequence, however, hybridize with equal efficiency to genomic DNA from jimpy and wild-type littermates, suggesting that the defect in the jimpy PLP mRNA is generated by aberrant RNA processing rather than by deletion of genomic sequences. We conclude that a mutation in the gene for PLP that leads to an incorrectly spliced RNA transcript is the primary defect of this genetic disorder.

Amino Acid Sequence↗
PubMed1985

Epidermal growth factor does not cross the blood-brain barrier.

To measure the passage of epidermal growth factor (EGF) through the blood-brain barrier (BBB) 125I-labeled EGF was injected intravenously into adult rats. The distribution of 125I-EGF in the blood and cerebrospinal fluid (CSF) was determined over a time period of several hours. Between 2 to 6 h a stable distribution of intact 125I-EGF in CSF was measured to be approximately 1/500 of the blood-borne EGF, an equilibrium value below those obtained by other investigators for BBB-impermeable compounds, such as inulin and bovine serum albumin. Our data indicate that 125I-EGF, although clearly detectable in the CSF, does not cross the BBB at a higher rate or in higher quantities than would be expected from its molecular size.

Animals↗
PubMed1985

Nucleotide sequences of two mRNAs for rat brain myelin proteolipid protein.

The 3200 and 1600 nucleotide mRNAs encoding rat brain proteolipid protein (PLP), the major protein component of central nervous system myelin, are heterogeneous at their 5' ends, differ in their 3' polyadenylation sites, and are transcribed from a single gene. The mRNAs, which first appear postnatally, encode identical 277 amino acid proteins that are 99% identical to the bovine protein sequence. Thus, PLP has been highly conserved during mammalian evolution. A single amino-terminal methionine is removed post-translationally, indicating that PLP does not require a signal peptide sequence for insertion into the myelin membrane. Mouse and monkey utilize the 3200 but not the 1600 nucleotide mRNA, suggesting that there is no functional necessity for two sizes of rat PLP mRNAs.

Amino Acid Sequence↗
PubMedDate not supplied

Differential expression of apoptotic markers in jimpy and in Plp overexpressors: evidence for different apoptotic pathways.

Point mutations and duplications of proteolipid protein (PLP) gene in mammals cause dysmyelination and oligodendrocyte cell death. The jimpy mouse, which has a lethal Plp point mutation, is the best characterized of the mutants; transgenic mice, which have additional copies of Plp gene, are less characterized. While oligodendrocyte death is a prominent feature in jimpy, the pathways leading to death have not been investigated in jimpy and Plp overexpressors. Using immunohistochemistry and immunobloting, we examined expression of cleaved caspase-3, Poly (ADP-ribose) polymerase (PARP), caspase-12, and mitochondrial apoptotic markers in spinal cord in jimpy males and Plp overexpressors. Compared to controls, cleaved caspase-3 is increased 10x in jimpy white matter spinal cord, and 3x in Plp overexpressor. In jimpy, the number of cleaved caspase-3 cells far exceeds the number of TUNEL(+) cells. The majority of cleaved caspase-3(+) cells were not TUNEL(+) and these cells exhibited staining in perikarya and in processes. Only 30% of the cleaved caspase-3(+) cells were TUNEL(+) and exhibited both nuclear and perinuclear staining. This observation suggests that activation of caspase-3 begins earlier and overlaps for a period of time with DNA fragmentation. In both Plp mutants, quantitative immunobloting of PARP showed a 45% increase in total as well as cleaved form, indicating that oligodendrocytes die via apoptosis. Most interestingly, cleavage of caspase-12, a caspase associated with unfolded protein response, is dramatically increased in jimpy but not at all in Plp overexpressors. Mitochondrial markers cytochrome c and Bcl-X(L) are upregulated in both Plp mutants but levels of expression are different between mutants, suggesting that apoptosis in these two Plp mutants follows different pathways. In jimpy, mitochondrial apoptotic markers may play a role in amplifying the apoptotic signal. Our data shows for the first time, in vivo, that mutations in Plp gene increase oligodendrocyte death by activating the caspase cascade but the trigger to upregulate this cascade follows different pathways.

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