Biomedical subjects
M Freeman
Publications and source records attributed to M Freeman.
EGF receptor/Rolled MAP kinase signalling protects cells against activated Armadillo in the Drosophila eye.
beta-catenin/Armadillo are transcriptional co-activators that mediate Wnt signalling in normal development. Activated forms of beta-catenin are oncogenic. We have constructed mutant forms of Drosophila Armadillo which correspond to common human oncogenic mutations, and find them to activate Armadillo constitutively. When expressed in the Drosophila eye, these eventually induce apoptosis in all cell types. Intriguingly, cells in the eye are resistant to the effects of activated Armadillo for a long period prior to the onset of cell death at the mid-pupal stage. This latency is conferred by EGF receptor (EGFR)/MAP kinase signalling, which prevents activated Armadillo from inducing apoptosis; when EGFR signalling naturally ceases, the cells rapidly die. Nemo, the Drosophila homologue of NLK in mice and LIT-1 in Caenorhabditis elegans, does not antagonize activated Armadillo, suggesting that the Nemo-like MAP kinases may not generally interact with Armadillo/beta-catenin. Thus, our results show that activated Armadillo is subject to a specific negative control by EGFR/Rolled MAP kinase signalling.
The Fontan procedure in adults.
SETTING: Tertiary adult congenital cardiac referral centre. DESIGN: Retrospective cross sectional analysis. OBJECTIVES: To report our 20 year experience with adult Fontan operations, and to compare late outcome in patients with single ventricle with definitive aortopulmonary or cavopulmonary shunt palliation. PATIENTS AND MAIN OUTCOME MEASURES: Patients older than 18 years undergoing Fontan operation between 1 January 1982 and 31 December 1998 were identified. Mortality and late outcome were derived from hospital records. These patients were compared with a cohort of 50 adults with single ventricle who had not undergone a Fontan operation. RESULTS: 61 adults, median age 36 years (range 18-47 years), with a median follow up of 10 years (range 0-21 years) were identified. Actuarial survival was 80% at one year, 76% at five years, 72% at 10 years, and 67% at 15 years. Compared with before the Fontan operation, more patients were in New York Heart Association (NYHA) functional class I or II at the latest follow up (80% v 58%, p < 0.001). Systolic ventricular function deteriorated during follow up such that 34% had moderate to severe ventricular dysfunction at the latest follow up compared with 5% before Fontan (p < 0.001). Arrhythmia increased with time (10% before Fontan v 57% after 10 years, p < 0.001). Fontan patients had improved NYHA functional class, ventricular function, atrioventricular regurgitation, and fewer arrhythmias than the non-Fontan group at the latest follow up. CONCLUSION: The Fontan operation in adults has acceptable early and late mortality. Functional class, systolic ventricular function, atrioventricular regurgitation, and arrhythmia deteriorate late after surgery but to a lesser degree than in non-Fontan patients with a single ventricle.
Notch signalling and the initiation of neural development in the Drosophila eye.
Neural determination in the Drosophila eye occurs progressively. A diffusible signal, Dpp, causes undetermined cells first to adopt a 'pre-proneural' state in which they are primed to start differentiating. A second signal is required to trigger the activation of the transcription factor Atonal, which causes the cells to initiate overt photoreceptor neurone differentiation. Both Dpp and the second signal are dependent on Hedgehog (Hh) signalling. Previous work has shown that the Notch signalling pathway also has a proneural role in the eye (as well as a later, opposite function when it restricts the number of cells becoming photoreceptors - a process of lateral inhibition). It is not clear how the early proneural role of Notch integrates with the other signalling pathways involved. We provide evidence that Notch activation by its ligand Delta is the second Hh-dependent signal required for neural determination. Notch activity normally only triggers Atonal expression in cells that have adopted the pre-proneural state induced by Dpp. We also report that Notch drives the transition from pre-proneural to proneural by downregulating two repressors of Atonal: Hairy and Extramacrochaetae.
Reflective logs: an aid to clinical teaching and learning.
This paper reports on the use of learning logs for clinical teaching and learning in a university clinic. Students were encouraged to submit a written summary of their reflections after each clinical session for discussion at the subsequent session. Evaluation has shown that clinician-teachers and students value this approach because it facilitates clear goal-setting, promotes information exchange and provides opportunities for explicit focus on the student's learning needs. Although most students reported that completion of the learning log is time-consuming, the majority considered that this was balanced by the benefits, including opportunities for additional feedback and the 'licence to ask questions'. The evaluation has also shown, however, that few students elected to use their learning logs in subsequent placements, particularly when these were undertaken away from the university clinic. Some possible reasons for this are explored.
World Health Day 2001--'mental health'.
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LBP, CD14, TLR4 and the murine innate immune response to a peritoneal Salmonella infection.
In mice, defense against an intraperitoneal Salmonella infection depends on a vigorous innate immune response. Mutations which lead to an inadequate early response to the pathogen thus identify genes involved in innate immunity. The best studied host resistance factor, NRAMP-1, is an endosomal membrane protein whose loss leads to an inability of the animals to hold the infection in check. However, innate defense against Salmonella is not restricted to mechanisms which directly attack the pathogen within macrophages. Here we have examined the contribution of the LBP, CD14 and TLR4 gene products to innate defense against Salmonella. To this end, we have generated mice which carry a wild-type allele of NRAMP-1, but which are deficient for the LBP, CD14 or TLR4 genes. Loss of any of these genes leads to a susceptibility to Salmonella as dramatic as that seen in animals lacking functional NRAMP-1 protein. This indicates that LBP, CD14 and TLR4 are all critical elements required in the proper induction of this innate defense system.
Feedback control of intercellular signalling in development.
The intercellular communication that regulates cell fate during animal development must be precisely controlled to avoid dangerous errors. How is this achieved? Recent work has highlighted the importance of positive and negative feedback loops in the dynamic regulation of developmental signalling. These feedback interactions can impart precision, robustness and versatility to intercellular signals. Feedback failure can cause disease.
Smoking is associated with the retention of cytoplasm by human spermatozoa.
OBJECTIVES: To determine whether cigarette smoking is associated with the abnormal retention of residual sperm cytoplasm in infertile men. METHODS: Semen samples were obtained from 87 consecutive non-azoospermic men with idiopathic infertility (18 smokers and 69 nonsmokers) and from 20 men presenting for vasectomy (fertile controls). Standard semen parameters and the percentage of spermatozoa with residual cytoplasm (on Papanicolaou smears) were recorded. RESULTS: Subject age, semen volume, and sperm density, motility, and morphology were not significantly different between the two groups of infertile men. However, a significant difference was found in the mean +/- SEM percentages of sperm with cytoplasm droplets between smokers and nonsmokers (12.9% +/- 1.7% and 8.1% +/- 0.9%, respectively; P < 0.001). CONCLUSIONS: Our data suggest that cigarette smoking is associated with retention of sperm cytoplasmic droplets in infertile men, a morphologic characteristic associated with impaired sperm function.
Evidence that Argos is an antagonistic ligand of the EGF receptor.
Argos, the inhibitor of the Drosophila epidermal growth factor (EGF) receptor, remains the only known extracellular inhibitor of this family of receptors in any organism. The functional domain of Argos includes an atypical EGF domain and it is not clear whether it binds to the EGF receptor or if it acts via a distinct receptor to reduce Egfr activity indirectly. Here we present two lines of evidence that strongly suggest that Argos directly interacts with the EGF receptor. First, Argos is unable to inhibit a chimeric receptor that contains an extracellular domain from an unrelated RTK, indicating the need for the EGF receptor extracellular domain. Second, Argos can inhibit the Drosophila EGF receptor even when expressed in human cells, implying that no other Drosophila protein is necessary for inhibition. We also report that Argos and the Drosophila activating ligand, Spitz, can influence mammalian RTK activation, albeit in a cell-type specific manner. This includes the first evidence that Argos can inhibit signalling in mammalian cells, raising the possibility of engineering an effective human EGF receptor/ErbB antagonist. Oncogene (2000) 19, 3560 - 3562
The notch signalling regulator fringe acts in the Golgi apparatus and requires the glycosyltransferase signature motif DXD.
BACKGROUND: Signalling via the Notch receptor is a key regulator of many developmental processes. The differential responsiveness of Notch-expressing cells to the ligands Delta and Serrate is controlled by Fringe, itself essential for normal patterning in Drosophila and vertebrates. The mechanism of Fringe action, however, is not known. The protein has an amino-terminal hydrophobic stretch resembling a cleaved signal peptide, which has led to the widespread assumption that it is a secreted signalling molecule. It also has distant homology to bacterial glycosyltransferases, although it is not clear if this reflects a shared enzymatic activity, or merely a related structure. RESULTS: We report that a functional epitope-tagged form of Drosophila Fringe was localised in the Golgi apparatus. When the putative signal peptide was replaced by a confirmed one, Fringe no longer accumulated in the Golgi, but was instead efficiently secreted. This change in localisation dramatically reduced its biological activity, implying that the wild-type protein normally acts inside the cell. We show that Fringe specifically binds the nucleoside diphosphate UDP, a feature of many glycosyltransferases. Furthermore, specific mutation of a DxD motif (in the single-letter amino acid code where x is any amino acid), a hallmark of most glycosyltransferases that use nucleoside diphosphate sugars, did not affect the Golgi localisation of the protein but completely eliminated in vivo activity. CONCLUSIONS: These results indicate that Fringe does not exert its effects outside of the cell, but rather acts in the Golgi apparatus, apparently as a glycosyltransferase. They suggest that alteration in receptor glycosylation can regulate the relative efficiency of different ligands.
A family of rhomboid-like genes: Drosophila rhomboid-1 and roughoid/rhomboid-3 cooperate to activate EGF receptor signaling.
As in mammals, the Drosophila EGF receptor controls many aspects of growth and development. The rate limiting component of Drosophila Egfr signaling is Rhomboid, a seven transmembrane domain protein, whose expression prefigures Egfr signaling. Little is known about the molecular mechanism of Rhomboid function but genetic evidence suggests that it controls the activation of the ligand Spitz, a TGFalpha-like factor. Spitz/Egfr signaling regulates cell determination in the eye but here there is no apparent function for Rhomboid, an observation that casts doubt on this prevailing model of Rhomboid function. We describe our identification of six new rhomboid-like genes in Drosophila, and a large family of related genes present in organisms as diverse as bacteria and mammals; a human rhomboid homolog has also recently been described. Drosophila rhomboid-3 corresponds to the roughoid mutation; it cooperates with rhomboid-1 to control Egfr signaling in the eye, thereby solving the puzzle of the apparent lack of Rhomboid-1 function there. Rhomboid-1 and Roughoid/Rhomboid-3 act in the signal-emitting not signal-receiving cell, supporting the idea that Spitz activation is regulated by Rhomboid-like molecules.
Varicocele is associated with abnormal retention of cytoplasmic droplets by human spermatozoa.
OBJECTIVE: To determine whether varicocele is associated with retention of sperm cytoplasmic droplets in infertile men. DESIGN: Retrospective study. SETTING: University infertility clinic. PATIENT(S): Nonazoospermic men with idiopathic (n = 69) and varicocele-associated infertility (n = 73), and 20 fertile controls presenting for vasectomy. INTERVENTION(S): None. MAIN OUTCOME MEASURES(S): Standard semen parameters and percentage of spermatozoa with cytoplasmic droplets on Papanicolaou smears. RESULT(S): No statistically significant differences were found between the fertile and infertile groups with respect to semen volume. Fertile controls had significantly greater mean percent sperm motility and normal morphology than infertile men. The mean percentage of sperm with residual cytoplasm was statistically significantly different in all three groups. Infertile men with varicocele had the highest percentage of sperm with cytoplasmic droplets, the next highest level being in men with idiopathic infertility and the lowest level in fertile controls (11.7 +/- 1.0, 8.1 +/- 0.9 and 3.2 +/- 0.4%, respectively, P<.0001). CONCLUSION(S): Our data show that idiopathic and even moreso, varicocele-related male infertility are conditions associated with impaired disposal of residual sperm cytoplasm by the testis and/or epididymis. These data provide a possible mechanism for the observed semen abnormalities and reduced fertility potential associated with varicocele and idiopathic male infertility.
Aldosterone modulates plasminogen activator inhibitor-1 and glomerulosclerosis in vivo.
BACKGROUND: Aldosterone promotes nephrosclerosis in several rat models, whereas aldosterone receptor antagonism blunts the effect of activation of the renin-angiotensin-aldosterone system (RAAS) on nephrosclerosis, independent of effects on blood pressure. Based on recent findings linking activation of the RAAS with impaired fibrinolytic balance, we hypothesized that aldosterone induces sclerosis through effects on plasminogen activator inhibitor-1 (PAI-1), the major physiological inhibitor of plasminogen activation. METHODS: We examined the effect of aldosterone antagonism on the development of sclerosis and on renal PAI-1 expression following radiation injury in the rat. Following a single dose of 12 Gy to the kidneys, male Sprague-Dawley rats were treated with placebo, the aldosterone antagonist spironolactone (4.5 mg/day by time-release subcutaneous pellet), the angiotensin type 1 receptor antagonist L158-809 (AT1RA; 80 mg/L drinking water), or combined spironolactone and AT1RA. RESULTS: Rats treated with placebo developed significant proteinuria and nephrosclerosis 12 weeks following radiation associated with hypertension. Kidney PAI-1 mRNA expression was increased eightfold (P < 0.001 vs. nonradiated controls). Spironolactone alone had no effect on blood pressure (systolic blood pressure 149.0 +/- 5.4 mm Hg) compared with placebo (151.6 +/- 11.2 mm Hg, P = NS), whereas AT1RA alone (107.7 +/- 8.9 mm Hg, P = 0.013 vs. placebo) or in combination therapy (102.1 +/- 6.2 mm Hg, P = 0.001 vs. placebo) lowered blood pressure. Both the AT1RA and spironolactone decreased proteinuria following radiation (P < 0.001 vs. placebo for either drug), and the combination of AT1RA + spironolactone had a greater effect on proteinuria than spironolactone alone (P = 0.003). Aldosterone antagonism significantly decreased (P = 0.016 vs. placebo) and AT1RA virtually abolished (P = 0.001 vs. placebo) the development of sclerosis. Spironolactone significantly decreased PAI-1 mRNA expression in the kidneys of radiated animals (PAI-1 mRNA/GAPDH ratio 0.39 +/- 0.13 vs. placebo 0.84 +/- 0.05, P = 0.006), and there was a significant correlation between the degree of sclerosis and the level of PAI-1 immunostaining within individual rats (R2 = 0.97, P < 0.0001). CONCLUSION: This study is, to our knowledge, the first to demonstrate that aldosterone regulates PAI-1 expression in vivo, and supports the hypothesis that aldosterone induces renal injury through its effects on PAI-1 expression.
No association between the NOS3 codon 298 polymorphism and Alzheimer's disease in a sample from the United States.
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Using all opportunities for improving mental health--examples from South Africa.
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The alpha-2 macroglobulin gene is not associated with Alzheimer's disease in a case-control sample.
Genetic association has recently been reported between alleles in the alpha-2-macroglobulin (A2M) gene and the occurrence of Alzheimer's disease (AD) in familial and sporadic samples. We have investigated the A2M intronic deletion polymorphism in a case-control study of 295 unrelated clinic and community-based AD cases, and compared these to a sample of 113 unrelated control individuals recruited as part of an epidemiological study. Our results show no association between A2M and AD in either case sample. Furthermore, A2M is not predictive of AD in an interactive fashion when considering APOE, race or gender. In a subset of our larger sample we have also investigated the A2M Val1000lle polymorphism, and again find no evidence for association. We conclude that there is no genetic association between A2M and AD in our case-control sample.