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Biomedical subjects

M McLeod

Publications and source records attributed to M McLeod.

At least 37 records · Page 2Linked to original sources
PubMed1995

The sak1+ gene of Schizosaccharomyces pombe encodes an RFX family DNA-binding protein that positively regulates cyclic AMP-dependent protein kinase-mediated exit from the mitotic cell cycle.

In Schizosaccharomyces pombe, meiosis is initiated by conditions of nutrient deprivation. Mutations in genes encoding elements of the cyclic AMP-dependent protein kinase (cAPK) pathway interfere with meiosis. Loss-of-function alleles of genes that stimulate the activity of cAPK allow cells to bypass the normal requirement of starvation for conjugation and meiosis. Alternatively, loss-of-function alleles of genes that inhibit cAPK lead to the inability to undergo sexual differentiation. The cgs1+ gene encodes the regulatory subunit of cAPK, and the cgs2+ gene encodes a cyclic AMP phosphodiesterase. Thus, both genes encode proteins which negatively regulate the activity of cAPK. Loss of either cgs1 or cgs2 prevents haploid cells from conjugating and diploid cells from undergoing meiosis. In addition to these defects, cells are unable to enter stationary phase. We describe a novel gene, sak1+, which when present on a plasmid overcomes the aberrant phenotypes associated with unregulated cAPK activity. Genetic analysis of sak1+ (suppressor of A-kinase) reveals that it functions downstream of cyclic AMP-dependent protein kinase to allow cells to exist the mitotic cycle and enter either stationary phase or the pathway leading to sexual differentiation. The sak1+ gene is essential for cell viability, and a null allele causes multiple defects in cell morphology and nuclear division. Thus, sak1+ is an important regulatory element in the life cycle of S. pombe. Sequence analysis shows that the predicted product of the sak1+ gene is an 87-kDa protein which shares homology to the RFX family of DNA-binding proteins identified in humans and mice. One member of this family, RFX1, is a transcription factor for a variety of viral and cellular genes.

Alleles↗
PubMed1991

Interaction between ran1+ protein kinase and cAMP dependent protein kinase as negative regulators of fission yeast meiosis.

In fission yeast, meiosis is initiated by transcriptional activation of the mei3+ gene under the combined influence of the four mating type genes. The mei3+ gene product acts as a meiotic inducer by binding to and inhibiting the ran1+ protein kinase. Inactivation of ran1+ kinase is both necessary and sufficient to allow meiotic differentiation. We describe a class of mutants which are unable to undergo both normal meiosis and meiosis induced by inactivation of ran1+. In addition to these defects, the cells are sterile and unable to enter stationary phase. We have determined that the mutants define two complementation groups, designated cgs1+ and cgs2+ (continues to grow in stationary). The wild type allele of each gene has been isolated and sequence analysis of cgs1+ shows that it encodes a protein homologous to the regulatory subunit of cyclic AMP dependent protein kinase (cAPK). Biochemical studies demonstrate that in cgs1-1 containing cells, cAPK activity is unregulated by cyclic AMP (cAMP). Sequence analysis of cgs2+ shows that the predicted protein it encodes shares homology with a phosphodiesterase from Dictyostelium discoideum and biochemical studies demonstrate that cells containing a mutant allele of cgs2+ have elevated levels of cAMP. Thus, both genes encode proteins that regulate the activity of cAPK. We have previously shown that cells overproducing ran1+ kinase are meiotically defective. Here, we provide direct evidence that the meiotic defect caused by either unregulated cAPK activity or unregulated ran1+ kinase activity is due to inability to induce transcription of the mei2+ gene, which is required for meiotic initiation. We propose that the switch from vegetative growth to meiosis in fission yeast requires inactivation of ran1+ kinase and is prevented by unregulated levels of cAPK.

Amino Acid Sequence↗
PubMed1991

Controlled trial of a home and ambulatory program for asthmatic children.

Care of asthmatic children is often episodic and more therapeutic than preventive. A 2-year randomized, controlled trial involving 95 children measured the impact of a comprehensive home and ambulatory program for pediatric asthma management using objective outcome measures. Interventions for the study group during the first year included 3-month clinic visits, education, and home visits by a specially trained research nurse. Control subjects continued to receive regular care from a family physician or pediatrician. Eight-nine subjects (93%) completed the study. Study subjects had less school absenteeism than control subjects (10.7 vs. 16.0 days, P = .04) and showed significantly better small airway function after 1 year. Asthma severity improved in 13 study subjects and worsened in 5. The reverse was true for control subjects. Study subjects exhibited better metered aerosol technique than control subjects (P = .0005). Fewer days were spent in hospital by the study subjects admitted compared with control subjects (3.67 vs 11.2 days, P = .02). After 1 year, more study than control families (72.1% vs 33.1%, P = .006) reported that their asthmatic child took responsibility for the asthma management. The intervention failed to reduce exposure to secondhand smoke or to household pets. There were no significant differences in medical visits, theophylline levels, or records of asthma symptoms. One year after discontinuing the intervention, a marked "washout" effect was observed. Comprehensive ambulatory programs of childhood asthma management can improve objective measures of illness severity but must be sustained.

Adolescent↗
PubMed1990

Secreted phosphoprotein mRNA is induced during multi-stage carcinogenesis in mouse skin and correlates with the metastatic potential of murine fibroblasts.

Secreted phosphoprotein I (SPP), also known as 2ar, osteopontin, 44-kDa bone phosphoprotein, bone sialoprotein I, and transformation-related phosphoprotein, is a 41.5-kDa glycosylated phosphoprotein secreted by many mammalian cell lines and expressed in a limited set of tissues. Using a cDNA probe, we found that SPP mRNA, which is barely detectable in normal mouse epidermis, was expressed at moderate-to-high levels in 2 of 3 epidermal papillomas and at consistently high levels in 7 of 7 squamous-cell carcinomas induced by an initiation-promotion regimen. This contrasts with the transient induction we had previously observed after a single application of the tumor promoter 12-O-tetradecanoylphorbol-13-acetate (TPA). In a set of 5 independently isolated T24-H-ras-transfected mouse C3H 10T1/2 cell lines, the levels of SPP mRNA correlated well with ras mRNA levels and with both experimental and spontaneous metastatic ability. SPP mRNA expression was also elevated in a derivative of mouse LTA cells transfected with genomic DNA from B16F1 melanoma cells and selected for increased experimental metastatic ability in the chick embryo. This apparent association of SPP expression with invasion, progression and metastasis, along with the presence of a functional ArgGlyAsp (RGD) cell adhesion site in SPP (osteopontin), leads us to propose that SPP may act as an autocrine adhesion factor for tumor cells.

Animals↗
PubMed1990

Primary peritoneal neuroblastoma: computed tomography findings.

Primary peritoneal tumors are rare neoplasms. The computed tomography findings in an adult patient with a primary peritoneal neuroblastoma are described. Discussion of these uncommon neoplasms and this unusual presentation of neuroblastoma forms the basis of this report.

Adult↗
PubMed1989

Regulation of meiosis: from DNA binding protein to protein kinase.

The transition from mitotic cell division to meiosis in yeast is governed by both the mating-type genes and signals from the environment. Analysis of mutants that are unable to regulate entry into meiosis has identified many genes that function in this process and in some cases, the biochemical activity of their protein products has been described. At least two of the the mating-type genes of Saccharomyces cerevisiae encode DNA binding proteins that regulate transcription of unlinked genes required for entry into meiosis. Meiotic development of the distantly related yeast, Schizosaccharomyces pombe, is also controlled by the mating-type genes but in this yeast, their role is to regulate expression of a protein that acts as an inhibitor of a protein kinase. The ability to use the powerful tool of genetics in yeast has provided us with many new insights into the problem of meiotic development.

DNA-Binding Proteins↗
PubMed1988

A specific inhibitor of the ran1+ protein kinase regulates entry into meiosis in Schizosaccharomyces pombe.

In fission yeast, meiosis is initiated by transcriptional activation of the mei3+ gene, under the combined influence of the four mating-type genes. The product of the mei3+ gene acts as a critical meiotic inducer by binding non-covalently to a newly identified protein kinase encoded by the ran1+ gene and inhibiting its enzymatic activity. Inactivation of the ran1+ protein kinase is both necessary and sufficient to divert a vegetative cell from mitotic division to meiotic differentiation.

Fungal Proteins↗
PubMed1988

Rat brain catecholamine release at 1, 10, 20, and 100 ATA heliox, nitrox, and trimix.

The pattern of neurotransmitter release in the rat caudate and hypothalamus was studied following exposure to pressure in combination with various gas mixtures. The caudate was selected for its control of extrapyramidal motor output. The hypothalamus was studied because of its involvement in autonomic responses. The neurotransmitters chosen for study were norepinephrine (NE) and dopamine (DA). Change of neurotransmitter concentration from control values and neurotransmitter turnover rate were chosen as measures of neuronal activity in the selected brain regions. Exposure to 100 ATA heliox resulted in a significant (P less than 0.05) increase in hypothalamic DA concentrations; however, NE concentrations remained relatively unchanged. One hundred ATA heliox produced the opposite effect on caudate DA concentrations; these values dropped to 1% of chamber control values. High partial pressures of nitrogen as seen with 100 ATA trimix and 20 ATA nitrox resulted in significant decreases in both DA and NE concentrations (both P less than 0.05) in the hypothalamus. These same exposures also produced significant decreases in DA concentrations in the caudate (P less than 0.05). Regional (caudate vs. hypothalamus) changes in neurotransmitter release in response to different pressures and/or gas mixtures may offer explanations for the physiologic and neurologic changes observed during nitrogen narcosis and high pressure nervous syndrome.

Animals↗
PubMed1987

The product of the mei3+ gene, expressed under control of the mating-type locus, induces meiosis and sporulation in fission yeast.

In fission yeast the ability to undergo meiosis and sporulation is conferred by the matP+ and matM+ genes of the mating-type locus. Inactivation of ran1+, a negative regulator of meiosis, is thought to be an essential step in meiotic initiation. We have isolated a further meiotic control gene mei3+, and have shown the following: a null allele of mei3 totally inhibits meiosis; the mei3+ RNA transcript and its translational product are expressed only in matP+/matM+ diploids entering meiosis; forced expression of mei3+ in vegetative cells provokes haploid meiosis and sporulation. We suggest that the product of mei3+ gene, a protein of 21 kd, initiates meiosis by inactivating ran1+.

Alleles↗
PubMed1986

Homology between the ran1+ gene of fission yeast and protein kinases.

The ran1+ gene of the fission yeast Schizosaccharomyces pombe is a negative regulator of both sexual conjugation and meiosis. The nucleotide sequence of the gene has been determined and contains a region of open reading frame (ORF) capable of encoding a protein of 52,000 daltons. S1 nuclease analysis of ran1+-encoded RNA showed that the ORF was spanned by an uninterrupted transcript. A fragment of DNA containing the entire ran1+ gene was expressed in a bacterial expression vector and found to encode the expected product of 52,000 daltons. The putative ran1+ gene product shares significant sequence homology with known protein kinases. The level of the ran1+ transcript was similar in vegetative and meiotic cells suggesting that the ran1+ protein product rather than its transcript is regulated during sexual differentiation.

Amino Acid Sequence↗
PubMed1986

An assessment of the Newcastle Anxiety Depression Index.

The Newcastle Anxiety and Depression Diagnostic Index (NADDI) has been reviewed, and its advantages and disadvantages discussed. One hundred eighty-seven patients were examined, and grouped into three categories by means of the NADDI, which produced a unimodal distribution of score. These three groups were studied in respect of the Hamilton Depression and SCL-90 self-rating scales. Significant profile differences were found on both scales. Patients with pure anxiety and pure depression were more distressed than the intermediate group of mixed anxiety-depressed patients. The NADDI scale items were compared in four clinical groups of primary endogenous, primary nonendogenous depression, generalized anxiety, and panic disorder. Most differences were found when panic disorder was compared to the other three groups, and generalized anxiety disorder received minimal validation. Treatment response was also examined.

Adult↗
PubMed1986

Identification of the crossover site during FLP-mediated recombination in the Saccharomyces cerevisiae plasmid 2 microns circle.

The FLP protein of the Saccharomyces cerevisiae plasmid 2 microns circle catalyzes site-specific recombination between two repeated segments present on the plasmid. In this paper we present results of experiments we performed to define more precisely the features of the FLP recognition target site, which we propose to designate FRT, and to determine the actual recombination crossover point in vivo. We found that essential sequences for the recombination event are limited to an 8-base-pair core sequence and two 13-base-pair repeated units immediately flanking it. This is the region identified as the FLP binding site in vitro and at which FLP protein promotes specific single-strand cleavages (B. J. Andrews, G. A. Proteau, L. G. Beatty, and P. D. Sadowski, Cell 40:795-803, 1985; J. F. Senecoff, R. C. Bruckner, and M. M. Cox, Proc. Natl. Acad. Sci. USA 82:7270-7274, 1985). Mutations within the core domain can be suppressed by the presence of the identical mutation in the chromatid with which it recombines. However, mutations outside the core are not similarly suppressed. We found that strand exchange during FLP recombination occurs most of the time within the core region, proceeding through a heteroduplex intermediate. Finally, we found that most FLP-mediated events are reciprocal exchanges and that FLP-catalyzed gene conversions occur at low frequency. The low level of gene conversion associated with FLP recombination suggests that it proceeds by a breakage-joining reaction and that the two events are concerted.

Base Sequence↗
PubMed1986

Interaction of the FLP recombinase of the Saccharomyces cerevisiae 2 micron plasmid with mutated target sequences.

The 2 micron plasmid of Saccharomyces cerevisiae codes for a site-specific recombinase, the FLP protein, that catalyzes efficient recombination across two 599-base-pair (bp) inverted repeats of the plasmid DNA both in vivo and in vitro. We analyzed the interaction of the purified FLP protein with the target sequences of two point mutants that exhibit impaired FLP-mediated recombination in vivo. One mutation lies in one of the 13-bp repeat elements that had been previously shown to be protected from DNase digestion by the FLP protein. This mutation dramatically reduces FLP-mediated recombination in vitro and appears to act by reducing the binding of FLP protein to its target sequence. The second mutation lies within the 8-bp core region of the FLP target sequence. The FLP protein introduces staggered nicks surrounding this 8-bp region, and these nicks are thought to define the sites of strand exchange. The mutation in the core region abolishes recombination with a wild-type site. However, recombination between two mutated sites is very efficient. This result suggests that proper base pairing between the two recombining sites is an important feature of FLP-mediated recombination.

Base Sequence↗
PubMed1984

Probing the limits of human deep diving.

Divers breathing compressed air are restricted to 45 m depth because of the narcotic effects of nitrogen and toxic action of oxygen at increased pressures. Substitution of oxygen-helium for compressed air has permitted divers to reach 600 m. However, at depths greater than 160 m, signs and symptoms of the high pressure nervous syndrome (h.p.n.s.) occur, with tremors, myoclonic jerking, nausea, vomiting, fatigue, somnolence, e.e.g. changes, dyspnoea, and poor sleep with nightmares. It has been the objective of this Laboratory to ameliorate the symptoms of pressure-induced h.p.n.s. by the addition of small amounts of 'narcotic' nitrogen to the oxygen-helium mixture to form the Trimix breathing gas. In 1973, comparative experiments with oxygen-helium and the same divers, during compressions in only 33 min to 219.5 m and 305 m, showed such Trimix to be effective with 10% (by volume) nitrogen. Simulated dives, termed ATLANTIS, have been made with Trimix over the last 4 years to depths in excess of 610 m for 11 days, 650 m for 4 days and 686 m for 1 day. The objectives were to determine the effects of either slow or rapid rates of compression, and either 5% or 10% (by volume) nitrogen in Heliox, on the presence of h.p.n.s. or nitrogen narcosis. Measurements were made of intellectual and psychomotor performance, electrophysiological function of the brain and reflexes, lung and cardiovascular function, including arterial gas analysis at rest and work, blood chemistry and psychiatric and psychological status. The results permit the conclusion that divers may be compressed safely to depths as great as 686 m. The technique requires a slow exponential compression over days, with frequent stages lasting 14 h or more, the use of 5-8% (by volume) nitrogen in Heliox and careful selection of the divers.

Atmospheric Pressure↗