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P Lockhart

Publications and source records attributed to P Lockhart.

16 recordsLinked to original sources
PubMed2001

Pruned median networks: a technique for reducing the complexity of median networks.

Observations from molecular marker studies on recently diverged species indicate that substitution patterns in DNA sequences can often be complex and poorly described by tree-like bifurcating evolutionary models. These observations might result from processes of species diversification and/or processes of sequence evolution that are not tree-like. In these cases, bifurcating tree representations provide poor visualization of phylogenetic signals in sequence data. In this paper, we use median networks to study DNA sequence substitution patterns in plant nuclear and chloroplast markers. We describe how to prune median networks to obtain so called pruned median networks. These simpler networks may help to provide a useful framework for investigating the phylogenetic complexity of recently diverged taxa with hybrid origins.

Base Sequence↗
PubMed1998

Fluconazole-resistant Candida species in the oral flora of fluconazole-exposed HIV-positive patients.

The purpose of this study was to examine the effect of preceding fluconazole treatment on the oral mycologic flora and on the sensitivity of oral Candida albicans isolates to fluconazole. Saline oral rinses were collected from 89 HIV-positive patients, of whom 48 had been exposed to fluconazole and 41 were fluconazole-naive. The rinses were cultured on Sabouraud's and Pagano Levin agars, and yeasts were identified by standard methods. Fluconazole sensitivity of C. albicans isolates was measured by disk diffusion assay. C. albicans was isolated from 69% of patients who had received fluconazole and from 93% of the patients who were fluconazole-naive (p < 0.05). Nine other species of yeasts were also isolated, most commonly C. glabrata. Five patients previously exposed to fluconazole harbored fluconazole-resistant C. albicans, whereas no resistance was detected among the patients who were fluconazole-naive (p < 0.01). Sixteen of the patients who were fluconazole-exposed carried yeasts other than C. albicans, compared with only five patients in the fluconazole-naive group (p < 0.01). All of the fluconazole-resistant strains were isolated from patients with low CD4 counts (less than 100 cells/ml) and after lengthy fluconazole exposures. Nevertheless, patients in Charlotte, N.C., who had a greater mean fluconazole exposure time (10.25 +/- 1.41 months) than patients in Glasgow, UK, (0.65 +/- 0.18 months; p < 0.005), did not develop significantly more in vitro resistance or species diversity. This study indicates that long-term fluconazole treatment can have significant effects on the yeast flora of the mouth, particularly in a patient with a CD4 count of less than 100 cells/ml.

Adult↗
PubMed1998

Evaluation of cerebellar size in attention-deficit hyperactivity disorder.

Evidence from animal and human research suggests that the cerebellum may play a role in cognition. This includes domains of executive function that are normally attributed to the prefrontal cortex and are typically deficient in individuals with attention-deficit hyperactivity disorder (ADHD). To investigate cerebellar structure in ADHD, magnetic resonance imaging morphometry was used to measure the area of the cerebellar vermis in 12 males with ADHD and 23 male controls matched for age and Wechsler Full-Scale IQ. Analyses were conducted to evaluate group differences, as well as differences between matched pairs of subjects with ADHD and those without ADHD. All measurements were corrected for overall brain size. Both analyses revealed that the size of the posterior vermis was significantly decreased in males with ADHD (P < .05 in both analyses), and that within the posterior vermis, the inferior posterior lobe (lobules VIII-X) was involved in this reduction (P < .05 for group analysis, P < .005 for matched pair analysis), while the superior posterior lobe (lobules VI/VII) was not involved in the reduction. The finding of abnormal inferior posterior vermal size suggests that dysfunction within this region of the cerebellum may underlie clinical deficits seen in individuals with ADHD.

Adolescent↗
PubMed1997

Molecular basis of the brindled mouse mutant (Mo(br)): a murine model of Menkes disease.

The brindled mouse mutant (Mo(br)) is the closest animal model of the human genetic copper deficiency, Menkes disease, which is presumed to be due to a mutation at the X-linked mottled locus (Mo). The mutant mice are hypopigmented and die at around 15 days after birth, but can be saved by treatment with copper before the 10th postnatal day. Menkes disease has been shown to be due to mutations of the gene ATP7A which encodes P-type ATPase (referred to here as MNK). MNK is likely to function in copper efflux from cells, but the full range of its biological activity is not fully understood. The nature of the mutation in the brindled mouse is of importance in our understanding of the role of MNK and for devising treatment strategies for Menkes disease. Here we show that the brindled mouse has a deletion of two amino acids in a highly conserved, but functionally uncharacterized, region of Mnk. Comparison with the Ca ATPases suggests this region may be involved in conformational changes associated with the E1/E2 transition fundamental to the action of P-type ATPases. We also describe the first Western blot data for Mnk in tissues, and these show normal levels of Mnk in mutant and brindled kidneys but none in liver. In the kidney, immunohistochemistry demonstrated Mnk in the proximal and distal tubules, the distribution is identical in mutant and normal. This distribution is consistent with Mnk being involved in copper resorption from the urine.

Adenosine Triphosphatases↗
PubMed1996

Ligand-regulated transport of the Menkes copper P-type ATPase efflux pump from the Golgi apparatus to the plasma membrane: a novel mechanism of regulated trafficking.

The Menkes P-type ATPase (MNK), encoded by the Menkes gene (MNK; ATP7A), is a transmembrane copper-translocating pump which is defective in the human disorder of copper metabolism, Menkes disease. Recent evidence that the MNK P-type ATPase has a role in copper efflux has come from studies using copper-resistant variants of cultured Chinese hamster ovary (CHO) cells. These variants have MNK gene amplification and consequently overexpress MNK, the extents of which correlate with the degree of elevated copper efflux. Here, we report on the localization of MNK in these copper-resistant CHO cells when cultured in different levels of copper. Immunofluorescence studies demonstrated that MNK is predominantly localized to the Golgi apparatus of cells in basal medium. In elevated copper conditions there was a rapid trafficking of MNK from the Golgi to the plasma membrane. This shift in steady-state distribution of MNK was reversible and not dependent on new protein synthesis. In media containing basal copper, MNK accumulated in cytoplasmic vesicles after treatment of cells with a variety of agents that inhibit endosomal recycling. We suggest that MNK continuously recycles between the Golgi and the plasma membrane and elevated copper shifts the steady-state distribution from the Golgi to the plasma membrane. These data reveal a novel system of regulated protein trafficking which ultimately leads to the efflux of an essential yet potentially toxic ligand, where the ligand itself appears directly and specifically to stimulate the trafficking of its own transporter.

Adenosine Triphosphatases↗
PubMed1995

Gene amplification of the Menkes (MNK; ATP7A) P-type ATPase gene of CHO cells is associated with copper resistance and enhanced copper efflux.

Three copper-resistant variants of cultured Chinese hamster ovary (CHO) cells were isolated and each was shown to accumulate less intracellular copper than the parental cells when grown in copper-supplemented media. The reduced copper accumulation was related to enhanced copper efflux. As cultured cells from patients with Menkes disease (mutations in MNK; ATP7A gene) accumulate copper, probably due to defective copper efflux, we investigated the possible role of the MNK gene in the molecular basis of copper resistance. We found increased MNK mRNA and MNK protein in all three resistant variants. The MNK protein, which has not been previously demonstrated experimentally in mammalian cells, was observed to have an apparent molecular weight of 178 kDa on SDS gels. The degree of increase in MNK mRNA and protein correlated well with the level of copper resistance and extent of copper efflux. By Southern blot and FISH analysis we determined that the molecular basis for overexpression of MNK was genomic amplification of the MNK gene. These data, combined with the clinical and cellular phenotype in Menkes disease, provide strong evidence that the MNK protein is involved in transmembrane copper efflux, and demonstrate a new system of gene amplification in mammalian cells.

Adenosine Triphosphatases↗
PubMed1994

Expression of the Menkes gene homologue in mouse tissues lack of effect of copper on the mRNA levels.

The expression of the homologue of the Menkes disease gene (Mnk) in mice was studied using RNA blots. The highest level of expression of the 8.0 kb mRNA was found in placenta, substantial expression was noted in lung, heart, brain, testis and kidney and gut mucosa, but very low levels were found in spleen and adult liver. In fetal liver, the amount of Mnk mRNA is similar to that found in kidney, however, it declines soon after birth. Results with copper-loaded normal mice and mutant mice with genetic defects in copper transport suggested that Mnk mRNA levels are not regulated by tissue copper concentrations.

Animals↗
PubMed1994

Mutations in the murine homologue of the Menkes gene in dappled and blotchy mice.

The murine homologue of the Menkes disease gene (MNK) was isolated from cDNA libraries, using human cDNA clones as probes, and by PCR. The predicted amino acid sequence shows a high level of identity (89.9%) with the human protein, and the predicted functional domains in the human protein are present. Using probes to the mouse Mnk gene, we found that the mottled dappled mutation was caused by alteration in the Mnk locus and lack of expression of Mnk RNA. Tissues of the blotchy mouse contained two larger sizes of MNK mRNA demonstrating a likely defect in RNA splicing. Thus, the mottled locus is homologous to the human MNK locus and dappled and blotchy are allelic mutations in this gene.

Adenosine Triphosphatases↗
PubMed1993

Isolation of a partial candidate gene for Menkes disease by positional cloning.

Menkes disease is an X-linked recessive disorder of copper metabolism resulting in death in early infancy. The gene has been mapped to band Xq13 based, in part, on a translocation breakpoint in a female with the disease, which was found to lie within 300 kilobases (kb) of the PGK-1 locus, allowing the isolation of a YAC clone spanning the breakpoint. Phage subclones from the breakpoint region were isolated and used to screen cDNA libraries. cDNA clones were found which detect an 8 kb transcript from normal individuals but show diminished or absent hybridization in Menkes disease patients. Partial sequence of the cDNA shows a unique open reading frame containing putative metal binding motifs which have been found in heavy metal resistance genes in bacteria. This gene is a strong candidate for the Menkes disease gene.

Adenosine Triphosphatases↗
PubMed1993

Isolation of glucagon antagonists by random molecular mutagenesis and screening.

Glucagon has an important role in the regulation of glucose homeostasis, and glucagon antagonists may be effective therapeutic agents in the control of diabetes mellitus. We were able to identify a number of analogs with antagonist activity by creating libraries of mutant glucagon coding sequences, expressing them in a yeast (Saccharomyces cerevisiae) secretion system, and screening for clones that produce analogs that inhibit the glucagon stimulation of rat hepatocyte membrane adenylate cyclase. These libraries were constructed by allowing random misincorporation during the synthesis of oligonucleotides that contained the complete coding sequence for mammalian glucagon or for an analog (desHis1-glucagon) that had partial antagonist activity. We developed and used a simplified screening assay to test culture broths from > 3500 individual transformant yeast clones for their ability to inhibit glucagon-dependent adenylate cyclase activity. Ultimately, > 20 different analogs with antagonist activity were identified by recovering and sequencing plasmid DNA from yeast strains that were positive in the screening assay. Interestingly, several analogs were identified repeatedly in independent yeast clones and certain amino acid substitutions occurred in more than one analog. This clustering of randomly isolated mutations clearly delineates the regions of the glucagon molecule that are important for designing improved glucagon antagonists. A subset of the antagonists identified in yeast broth were produced by peptide synthesis to confirm their activities as pure compounds.

Adenylyl Cyclases↗
PubMed1989

Development of a DNA probe from the deoxyribonucleotide sequence of a 3-N-aminoglycoside acetyltransferase [AAC(3)-I] resistance gene.

The aacC1 gene encoding the 3-N-aminoglycoside acetyltransferase [AAC(3)-I] was cloned from enteric plasmid pJR88, and its deoxyribonucleotide sequence was determined. Significant nucleotide homology was noted in the region extending from the proposed -35 sequences through the first 59 base pairs of the aacC1 gene open reading frame (ORF) and the upstream flanking regions and ORFs of several other antibiotic resistance genes. Sequences were noted to be homologous with the 6'-N-aminoglycoside acetyltransferase [AAC(6')-I], 2''-O-aminoglycoside adenylyltransferase [AAD(2'')], and 3''-O-aminoglycoside adenylyltransferase [AAD(3'')] resistance genes; the OXA-1, OXA-2, and PSE-2 beta-lactamase genes; and several dihydrofolate reductase genes. Small regions of homology were noted in the 3'-flanking regions of these resistance genes as well. A DNA probe for the aacC1 gene was selected from the nucleotide sequence information and was tested against a series of genetically and enzymatically defined strains. The probe, which proved specific for the aacC1 gene, was then tested against a series of 58 gentamicin-susceptible and 219 gentamicin-resistant gram-negative bacilli isolated from patients at the Seattle Veterans Administration Medical Center. Only six clinical isolates were noted to carry the aacC1 gene. Each was resistant to gentamicin but susceptible to kanamycin, tobramycin, and amikacin. The presence of homologous regions of DNA at both the 3' and 5' ends of the aacC1 gene reinforces the importance of choosing probes from within the ORFs of genes and of avoiding flanking sequences. When the homology with other sequences extends into the ORF, as it does with the aacC1 gene, development of a specific probe may require determination of the nucleotide sequence.

Acetyltransferases↗
PubMed1984

Advanced squamous carcinoma of the head and neck. A preliminary report of neoadjuvant chemotherapy with cisplatin, bleomycin, and methotrexate.

Between Oct 1, 1979 and Aug 1, 1982, 93 patients with advanced squamous carcinoma of the head and neck were given neoadjuvant treatment with cisplatin, bleomycin sulfate, and methotrexate before standard local treatment. Ninety-three patients were evaluable for response. The response rates were as follows: complete response, 24%; partial response, 64%; and no response, 12%. Differences in primary tumor site, performance status at presentation, histologic grade, and tumor size did not correlate with response to this chemotherapy. For patients achieving notable tumor reduction to 2 cm or less, standard local treatment with either surgery plus radiotherapy or high-dose radiotherapy alone was effective in controlling local disease. For patients with larger tumor masses following neoadjuvant chemotherapy, surgical resectability appeared to improve local control rates. In our series, patients not receiving maximal standard local treatment often had relapse of local disease despite favorable responses to chemotherapy.

Adolescent↗
PubMed1980

Oral pathoses as diagnostic indicators in leukemia.

A retrospective chart review of 500 leukemia patients was carried out to analyze the role of oral pathoses in the presentation of leukemia and to determine those factors which affect the frequency of oral involvement during the initial clinical phases of the disease. The data indicate that oral pathoses were frequent signs or symptoms in patients with undiagnosed acute leukemia but were less prevalent in patients with undiagnosed chronic leukemia. Neither age nor sex appeared to be a significant factor affecting oral involvement. Oral signs of thrombocytopenia were the most prevalent complaint of patients seeking diagnosis for their leukemia because of an oral problem, and they were also most frequently responsible for oral problems found at initial physical examination. Head and neck lymphadenopathy was also a frequent presenting sign or symptom. Dentists were responsible for initiating the diagnosis of leukemia in a significant number of patients with acute nonlymphoblastic leukemia.

Adolescent↗
PubMed1979

Delayed extraoral hypersensitivity to dental composite material.

Despite their similarities to acrylic resins, composite resins have not been reported to cause allergies. This report documents the case of a patient who experienced several delayed hypersensitivity reactions associated with epoxy-based materials, including dental composite resin. Patch testing confirmed her hypersensitivity to the composite materials. Removal of the composite restorations and replacement with acrylic restorations did not trigger further allergic reactions. Dentists using composite resin materials should be aware of both the possibility of delayed extraoral manifestations of hypersensitivity to those materials and the management of these patients.

Adult↗