PubMed Health⌕ Search

Biomedical subjects

P Montague

Publications and source records attributed to P Montague.

9 recordsLinked to original sources
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↗
PubMed1992

Developmental expression of major myelin protein genes in the CNS of X-linked hypomyelinating mutant rumpshaker.

Rumpshaker (rsh) is an X-linked mutation causing hypomyelination of the CNS of mice and has recently been identified as an allele of jimpy (jp). The mutation (known as jprsh) differs in several respects from other X-linked myelin mutants, including jp, in that mice have normal longevity, oligodendrocyte numbers are not decreased, and cell death is not a feature. Myelin sheaths are deficient in immunostainable PLP protein. The present study examines the developmental expression of the major myelin protein genes and translatability of PLP and MBP mRNA. Differences between the spinal cord and brain of mutants are evident in that mRNA levels are more markedly decreased in the brain. Protein levels are severely reduced in both locations and to a proportionately greater extent than the mRNA, particularly in the spinal cord where PLP RNA and protein are approximately 80% and 10-20%, respectively, of age-matched wild type mice. DM-20 protein, the other major product of the PLP gene, is disproportionately expressed in rumpshaker as is a 10 kDa proteolipid. In vitro translation studies indicate a marked decrease in PLP translation products from mutant RNA. There is no deficiency in the number of PLP mRNA-expressing oligodendrocytes although the abundance per cell is reduced. The data suggest that the phenotypic effects of the mutation may be associated with reduced translation of major myelin proteins, in particular PLP and its incorporation into compact myelin. However, the mutation is compatible with survival of oligodendrocytes and their differentiation to the stage of expressing PLP/DM-20 mRNA.

Aging↗
PubMed1992

Nitrate reductase and nitrite reductase transcript levels in various mutants of Aspergillus nidulans: confirmation of autogenous regulation.

The regulation of the expression of the A. nidulans niiA and niaD genes (encoding nitrite reductase and nitrate reductase activities, respectively) was investigated by Northern blotting. It was demonstrated that expression of the niiA and niaD genes is controlled at the level of mRNA accumulation and that mutations within the nirA and areA regulatory genes, as well as certain mutations within niaD itself or cnxE (for its molybdenum cofactor), markedly affect niiA and niaD transcript levels.

Aspergillus nidulans↗
PubMed1991

crnA encodes a nitrate transporter in Aspergillus nidulans.

The nucleotide sequence of the Aspergillus nidulans crnA gene for the transport of the anion nitrate has been determined. The crnA gene specifies a predicted polypeptide of 483 amino acids (molecular weight 51,769). A hydropathy plot suggests that this polypeptide has 10 membrane-spanning helices with an extensive hydrophilic region between helices six and seven. No striking homology was observed between the crnA protein and other reported membrane proteins of either prokaryotic or eukaryotic organisms, indicating that the crnA transporter may represent another class of membrane protein. Northern blotting results with wild-type cells show that (i) control of crnA expression is subject to nitrate (and nitrite) induction as well as nitrogen metabolite repression and (ii) regulation of the crnA gene is exerted at the level of mRNA accumulation, most likely at transcription, in response to the nitrogen source in the growth medium. Furthermore, similar studies with mutants of nirA and areA control genes and the niaD nitrate reductase structural gene show that crnA expression is mediated by the products of nirA (nitrate induction control gene), areA (nitrogen metabolite repression control gene), and niaD (involved in autoregulation of nitrate reductase).

Amino Acid Sequence↗
PubMed1991

Heterologous expression and regulation of the Neurospora crassa nit-4 pathway-specific regulatory gene for nitrate assimilation in Aspergillus nidulans.

The nirA gene of Aspergillus nidulans and the nit-4 gene of Neurospora crassa appear to be equivalent pathway-specific regulatory genes which mediate nitrate induction of nitrate reductase and nitrite reductase (NR and NiR) activities. We have transformed the nit-4 wild-type (wt) gene into the A. nidulans loss-of-function (pleiotropic negative) nirA 1 mutant strain. The nit-4 gene was found to complement the nirA 1 mutation, thus permitting the nirA 1 mutant strain to grow on nitrate or nitrite as the sole source of nitrogen. Integration of the nit-4 gene in transformants appears to have occurred at a number of 'ectopic', i.e. non-nirA, sites. Nitrate is required for the induction of NR activity in nit-4-transformed strains whilst NR production remains markedly subject to nitrogen-metabolite repression. However, NR levels are modestly higher than wt under all growth conditions.

Aspergillus nidulans↗
PubMed1989

Nucleotide sequence and regulation of expression of the Aspergillus nidulans gdhA gene encoding NADP dependent glutamate dehydrogenase.

The nucleotide sequence of the Aspergillus nidulans gdhA gene encoding NADP linked glutamate dehydrogenase has been determined and Northern blot analysis used to study the regulation of expression of this gene. The gdhA gene is 1485 nucleotides long and, by comparison with the corresponding Neurospora crassa am gene, has two putative introns of 53 nucleotides and a protein encoding region of 1380 nucleotides that codes for an inferred protein of 49.63 kDa which shows regions of homology with glutamate dehydrogenase proteins from a range of organisms. mRNA analysis of wild-type mycelium grown under a variety of conditions shows that: (a) the highest levels are seen with glucose as the carbon source with inorganic nitrogen; and (b) no gdhA mRNA is detectable when cells are transferred to amino acids as sole carbon source, closely matching the observed glutamate dehydrogenase activity levels under identical conditions. The results presented strongly suggest that a good carbon source is a prerequisite for transcription, but the molecular mechanism responsible is unclear.

Amino Acid Sequence↗
PubMed1985

Tissue specific transcription of the human epsilon-globin gene following transfection into the embryonic erythroid cell line K562.

We have introduced a plasmid containing the human epsilon-globin gene either stably or transiently into a number of erythroid or non-erythroid cell lines, and analysed the accuracy and efficiency of transcription. In non-erythroid cells (or in mouse erythroleukaemia (MEL) cells in which adult but not embryonic globin genes are expressed) transcription of the epsilon-globin gene occurs mainly from a site 200 bp upstream of the major cap site (the -200 cap site). In the human K562 cell line, in which the endogenous epsilon-globin gene is transcribed at high levels, transcription initiation from the introduced gene occurs mainly from the major cap site. Transcriptional activity of the epsilon-globin gene introduced into K562 cell is quantitatively similar to that of the endogenous gene. This suggests the presence (or absence) in K562 cells of factor(s) which activate (or repress) the epsilon-globin gene in a tissue specific manner.

Cell Line↗
PubMed1985

Distant sequences which regulate globin genes.

Besides the major cap site, transcription of the human epsilon-globin gene initiates at several upstream sites, the furthest 4.5 kb away. The upstream initiation sites occur in regions of hypersensitivity to DNaseI. There is also a very prominent DNaseI hypersensitive site 6.5 kb upstream which corresponds to an unusual nucleotide sequence. Upstream promoters, particularly one 200 bp upstream can be regulated independently of the major cap site. This site behaves as if it were a unidirectional enhancer. A fragment upstream of the mouse beta-globin promoter acts as a negative regulator in cis; it contains a long stretch of alternating purine and pyrimidine bases. The significance of upstream regulatory sequences adjacent to globin genes is discussed.

Base Sequence↗