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R W Davies

Publications and source records attributed to R W Davies.

At least 19 recordsLinked to original sources
PubMed1997

Developmental expression of the murine Mobp gene.

In this report we describe the developmental expression of the murine (Mobp) gene encoding myelin-associated oligodendrocytic basic protein. We have characterized three Mobp cDNA clones which have been used as probes. Murine Mobp splice variant-1 (mmsv-1), a portion of 3' untranslated region (UTR), is homologous to 3' UTR sequences found in the rat Mobp splice variants rOP1, Mobp81-A and Mobp-99. The mmsv-2 sequence, encoding 81 amino acids, closely resembles the rat Mobp81-A splice variant. The mmsv-3 cDNA, encoding 170 amino acids corresponding closely to the rat rOPRP1 splice variant, detects a single mRNA species present in low levels from E12 onward, suggesting this MOBP may have a function alternative or additional to involvement in myelin formation. The mmsv-1 probe detects an mRNA species abundantly expressed in the postnatal central nervous system (CNS) but barely detectable at E18. This mRNA is located initially in the cell bodies of oligodendrocytes, moving distally into their processes as myelination proceeds. The most abundant mmsv(s) in the adult CNS are present at detectable levels after expression of the myelin basic protein (Mbp) gene and marginally after or coincident with the proteolipid protein (Plp) gene. The level of the abundant, late-expressed mRNA correlates closely with the capacity to form myelin and the maturity of oligodendrocytes, as shown in two hypomyelinated mutants, rumpshaker and jimpy, which represent mildly and severely affected phenotypes, respectively.

Animals↗
PubMed1997

Sequence analysis of 497 mouse brain ESTs expressed in the substantia nigra.

The use of subtracted, region-specific cDNA libraries combined with single-pass cDNA sequencing allows the discovery of novel genes and facilitates molecular description of the tissue or region involved. We report the sequence of 497 mouse expressed sequence tags (ESTs) from two subtracted libraries enriched for cDNAs expressed in the substantia nigra, a brain region with important roles in movement control and Parkinson disease. Of these, 238 ESTs give no database matches and therefore derive from novel genes. A further 115 ESTs show sequence similarity to ESTs from other organisms, which themselves do not yield any significant database matches to genes of known function. Fifty-six ESTs show sequence similarity to previously identified genes whose mouse homologues have not been reported. The total number of ESTs reported that are new for the mouse is 407, which, together with the 90 ESTs corresponding to known mouse genes or cDNAs, contributes to the molecular description of the substantia nigra.

Animals↗
PubMed1997

Mortality, preference, avoidance, and activity of a predatory LeechExposed to cadmium.

The effects of cadmium on the hatching success of thecocoons of the freshwater predatory leech Nephelopsis obscura wereexamined together with the survivorship of hatchlings, changes in 96-hLC50 with biomass, preference-avoidance responses and changes inactivity. The 96-h EC50 for cocoons was 832.6 microg Cd/L with adecreasing bounded monotonic function best describing hatchling success as afunction of Cd concentration. Exposure of cocoons to Cd had a highlysignificant effect on post-hatchling survivorship with survivorship ofhatchlings from the 0-500-microg Cd/L concentrations not significantlydifferent from each other but higher than survivorship of hatchlings fromcocoons exposed to 1,000-4,000 microg Cd/L. Resistance to acute Cd toxicity,measured as LC50, increased with leech biomass. Inpreference-avoidance tests large leeches (>450 mg) spent more time in 100-and 200-microg Cd/L than in control water or in 50-microg Cd/L, while smallleeches (<250 mg) spent more time in 200-microg Cd/L compared to controlwater or 50-100-microg Cd/L. Leeches exposed to 100- and 200-microg Cd/Lexhibited a significant decrease in activity compared to the leeches in thecontrol and 50-microg Cd/L treatments.

Animals↗
PubMed1996

Neostriatal dopamine depletion and locomotor abnormalities due to the Albino Swiss rat agu mutation.

The sub-strain of Albino Swiss rat (AS/AGU) is a spontaneous mutation characterised by an ungainly, staggering gait, hindlimb rigidity, whole body tremor and (when symptoms are fully developed) difficulty in initiating movement; it exhibits a progressive decrease in dopaminergic cells within the substantia nigra. A breeding programme involving Albino Swiss (AS) and AS/AGU parent rats was used to produce the F1 offspring of AS x AS/AGU matings and, subsequently, F1 x AS/AGU back crosses. When adult, the movement of all animals was assessed blind by observers on three occasions, each animal being identifiable by a subcutaneous transponder implanted before weaning. All AS/AGU and half the F1 x AS/AGU back cross animals had abnormal gait, while all AS, F1 and the remaining F1 x AS/AGU backcross animals showed normal gait, implying that the mutation is recessive. Brains of males aged 12-15 months (n = 10 per group) were sectioned transversely on a cryostat (-20 degrees C) to produce a cut face just caudal to the anterior commissure (approximately Bregma -0.5 mm) and 1 mm diameter x 1 mm deep micropunches were taken from three areas of the caudate-putamen. Levels of dopamine were measured in all samples by high performance liquid chromatography with electrochemical detection (HPLC-ECD) followed by protein estimation. Levels of dopamine in the dorsal and middle caudate-putamen varied according to a simple inheritance pattern, being high in males from AS, F1 and F1 x AS/AGU back crosses without locomotor impairment, but lower in AS/AGU and F1 x AS/AGU back crosses with disordered gait. Dopamine levels in the ventral caudate-putamen did not show such a clear variation.

Animals↗
PubMed1995

Discovering genes with localised expression in the mouse brain: cDNAs specific to the substantia nigra.

Many important phenomena of normal brain physiology and disease are likely to be related to the function of genes expressed in localised regions of the brain. We show that subtracted libraries enriched in clones corresponding to rare mRNAs, which must include genes with very localised and neuron-specific expression, can easily be produced from single-stranded directional cDNA libraries after hybridization to excess photobiotinylated opposite-stranded cDNA (or RNA) from another brain region, followed by the removal of biotinylated molecules. We also demonstrate the use of heterologous probes from anatomically precise small regions of bovine brain to identify cDNA clones that putatively represent mRNAs present at significantly higher levels in a substantia nigra mRNA population enriched for pars compacta mRNA than in the total ventral midbrain or cerebellar mRNA population. Some of these cDNAs may identify genes that play important roles in the specific molecular biology of dopaminergic neurons, including susceptibility to Parkinson's disease.

Animals↗
PubMed1994

Enhanced access to rare brain cDNAs by prescreening libraries: 207 new mouse brain ESTs.

To use single-pass cDNA sequencing to characterize low-frequency cDNA clones from a region of the brain that includes the primary site of neurodegeneration in human Parkinson disease, we have developed a prescreening procedure using single brain region first-strand cDNA probes. Selection of cDNA clones giving low hybridization signals allowed the elimination of clones resulting from abundant messages and enrichment for clones corresponding to low-copy messages. Comparative sequencing of standard and prescreened cDNA libraries (191 and 124 clones, respectively) showed that this procedure raised the frequency of novel sequences encountered from 54 to 81%. The increased proportion of novel ESTs justifies the labor of prescreening. Automation of this procedure will accelerate the molecular description of genes expressed in any brain region, or any tissue, and represents a way to maximize access to cDNA sequences for human and mouse genome characterization. In total, the comparative sequencing experiments generated 207 new mouse and 11 new rat brain ESTs.

Animals↗
PubMed1994

The bioenergetic costs of specific dynamic action and ammonia excretion in a freshwater predatory leech Nephelopsis obscura.

The energy utilized by the predatory freshwater leech for specific dynamic action (SDA) and exogenous excretion, and the proportion of absorbed energy available for growth and/or activity were determined at 5, 10, 15, 20 and 25 degrees C. SDA and exogenous ammonia excretion increased with increases in temperature to 20 degrees C but decreased at 25 degrees C. The duration of SDA decreased from 19 hr at 5 degrees C to 11 hr at 25 degrees C, while the duration of exogenous excretion decreased from 22 hr at 5 degrees C to 11 hr at 25 degrees C. The proportion of absorbed energy utilized for SDA and exogenous excretion decreased from 5 degrees C to 15 degrees C and increased at 25 degrees C; however the energy available for growth and activity increased from 7.4 J/day at 5 degrees C to a maximum of 32.6 J/day at 15 degrees C, decreasing to 12.7 J/day at 25 degrees C.

Ammonia↗
PubMed1994

Reverse genetics of the mouse central nervous system: targeted genetic analysis of neuropeptide function and reverse genetic screens for genes involved in human neurodegenerative disease.

The development of gene targeting technology in mouse embryonic stem cells allows reverse genetics to be used to investigate the function of any cloned gene in the developing and adult brain. Promoter-trap, replacement and insertion vector strategies can be used to generate defined mutations in the chromosomal copy of a cloned gene in embryonic stem cells. These cells can be used to make chimaeric mice, some of which transmit the in vitro mutation via the germline to transgenic offspring. The phenotype of complete loss-of-function mutations (gene knock-outs) can be studied at molecular, cell biological, neurophysiological and behavioural levels, and allows inferences about gene function to be made. Precise small mutations can also be made using integrative vector or two-step replacement vector strategies, allowing specific questions to be asked about regulation and protein structure-function relationships. Reverse genetics can therefore be used as an alternative or additional approach to pharmacology for the study of molecular functions in the central nervous system. Reverse genetic studies of the involvement of particular molecules in neurological disease syndromes may be superior to pharmacological studies to the extent that the syndrome is determined by genetic predisposition. The general ways in which reverse genetics of the mouse can be used to ask questions about molecules in the central nervous system are illustrated by examples from ongoing work of this laboratory. Neuropeptides are an important class of transmitters in the brain, but only in very few cases have specific CNS functions been assigned to a particular neuropeptide. Targeted mutation of neuropeptide precursor and receptor genes offers a rapid way to learn about neuropeptide function. Complete loss-of-function mutations will provide information on any developmental roles of a neuropeptide and on overall behavioural and physiological effects of loss-of-function. More specific targeted mutations allow dissection of the individual roles of multiple neuropeptides that derive from a common precursor protein, and allow in vivo studies of the functional importance of particular amino acids. Experimental progress towards targeted mutation of the neurotensin receptor is described as an example. Recent technological improvements makes targeted mutation of a number of genes possible. This allows reverse genetic screening to be undertaken for genes involved in particular neurobiological phenomena: genes are identified on the basis of molecular criteria (e.g. expression pattern), and gene-targeting used to check their relevance to a phenotype. Neurodegenerative disease is an important aspect of the human phenotype.(ABSTRACT TRUNCATED AT 400 WORDS)

Amino Acid Sequence↗
PubMed1993

Heterologous protein secretion directed by a repressible acid phosphatase system of Aspergillus niger.

A new expression-secretion system of Aspergillus niger which directs the secretion of heterologous proteins is described. The promoter and signal peptide-encoding region of the phosphate-repressible aphA gene of A. niger, when fused to the coding region of the human interferon alpha 2 (hIFN alpha 2)-encoding gene (hIFN alpha 2), drives the expression of this gene and the secretion of the hIFN alpha 2 protein. Synthesis of hIFN alpha 2 in either A. niger or A. nidulans transformants carrying these constructs was regulated by inorganic phosphate (Pi) present in the medium, so that derepression of heterologous protein expression can be attained by lowering Pi concentration.

Acid Phosphatase↗
PubMed1993

Characterization of an Aspergillus nidulans genomic DNA fragment conferring phosphate-non-repressible acid-phosphatase activity.

A clone from an Aspergillus nidulans library was identified by its ability to confer enhanced staining for acid phosphatase (APase) activity upon phosphatase-deficient A. nidulans mutants. This APase activity is not repressed by high phosphate concentrations in the medium. The 2.9-kb nucleotide sequence in the region of the clone responsible for the effect reveals two potential protein-coding genes with a common N terminus. One corresponds to an open reading frame (ORF) with no introns, encoding 330 amino acids (aa). The other, shorter gene encoding 113 or 117 aa has the first 65 or 69 codons in common with the long ORF; then, after a single 165-nt intron with a fungal consensus lariat sequence and splice junctions, there are a further 48 codons in a different reading frame. Both correspond in sense direction, and the shorter gene in length, with the only detectable transcript in this region, but both differ from all known APase sequences. The possible identity of these ORFs with the pacG gene is discussed.

Acid Phosphatase↗
PubMed1993

Extrahepatic lipogenesis contributes to hyperlipidemia in the analbuminemic rat.

Hepatic lipid and apolipoprotein synthesis is increased in the nephrotic syndrome. Catabolism of triglyceride-rich lipoproteins is impaired in nephrotic syndrome but not in rats with hereditary analbuminemia (NA), suggesting that lipid synthesis should be increased by analbuminemia in the absence of proteinuria. In this study the rate of cholesterol and fatty acid synthesis in liver and extrahepatic tissue was measured in female NA and control Sprague-Dawley (SD) rats to determine whether lipid synthesis was indeed increased in isolated analbuminemia and to identify the site(s) of increased lipogenesis. We also measured the concentrations of apolipoproteins (apo) AI, B, and E in plasma, as well as the levels of the respective mRNAs in liver. Plasma cholesterol, triglycerides, and apo AI, B, and E were all increased severalfold in the NA rat (P < 0.001). Although liver apolipoprotein mRNA content was significantly increased (P < 0.001) for apo AI (643%), B (273%), and E (299%), 3-hydroxy-3-methylglutaryl-coenzyme A reductase activity in liver microsomes and hepatic cholesterol synthesis were not significantly increased in the NA rats. Hepatic fatty acid synthesis and intestinal cholesterol synthesis were not increased in the NA rats. Surprisingly, intestinal fatty acid synthesis was elevated by 60% (P < 0.01). The NA rats demonstrated approximately fourfold increases in the incorporation of 3H2O into circulating cholesterol and fatty acids (P < 0.001). A 56% increase in the synthesis of total nonsaponifiable lipid was found in the extravisceral carcass (P < 0.01).(ABSTRACT TRUNCATED AT 250 WORDS)

Animals↗