Showing papers by "Medical Research Council published in 1989"

The molecular basis of muscular dystrophy in the mdx mouse: a point mutation

Abstract: The mdx mouse is an X-linked myopathic mutant, an animal model for human Duchenne muscular dystrophy In both mouse and man the mutations lie within the dystrophin gene, but the phenotypic differences of the disease in the two species confer much interest on the molecular basis of the mdx mutation The complementary DNA for mouse dystrophin has been cloned, and the sequence has been used in the polymerase chain reaction to amplify normal and mdx dystrophin transcripts in the area of the mdx mutation Sequence analysis of the amplification products showed that the mdx mouse has a single base substitution within an exon, which causes premature termination of the polypeptide chain

Lexical representation and process

Abstract: How do humans understand and produce language? "Lexical Representation and Process" is the first collection to cover the full range of lexical representations and their role in language processing. The 18 contributions focus on psychological models of lexical processing, the nature of the input, lexical structure and process, and parsing and interpretation. "Lexical Representation and Process "provides a coherent and well documented frame of reference for a field of study that is becoming a central to both linguistics and psycholinguistics. It includes a wide variety of approaches from the radical alternative of new connectionist models, through new developments in traditional symbolic approaches, to the reemphasis on linguistic concepts as a crucial input to psycholinguistic models. The contributors are William Marslen Wilson, Ken Forster, Mark Seidenberg, Gary Dell, Dennis Matt, Jeff Elman, Keith Rayner, David Balota, Derek Besner, James Johnston, Uli Frauenfelder, Aditi Lahiri, Anne Cutler, Leslie Henderson, Jorge Hankamer, Rob Schreuder, Ino Flores D'Arcais, Lyn Frazier, Lorraine Tyler, Mark Steedman, Mike Tanenhaus, and Greg Carlson. William Marslen Wilson is a Senior Scientist at the Medical Research Council Applied Psychology Unit in Cambridge, England. A Bradford Book

Two classes of cortical gaba neurons defined by differential calcium binding protein immunoreactivities

Abstract: Calcium ions play a key role in many aspects of neuronal behavior and certain calcium binding proteins that may influence this behavior are differentially distributed in the central nervous system. In this study it is shown that immunoreactivity for calbindin-28 and for parvalbumin is localized in separate populations of inhibitory GABA interneurons in all areas of the neocortex of Old World monkeys. Virtually all GABA neurosn show immunoreactivity for one or other calcium binding protein but, except for a few cells in layer IV, GABA cells do not show immunoreactivity for both proteins. Among the two cell populations, parvalbumin immunoreactivity characterizes basket neurons while calbindin immunoreactivity characterizes double bouquet neurons. These findings suggest that the two GABA cell types differ in their regulation of calcium homeostasis and may yield clues to their different roles in intracortical circuitry.

Antibodies to blood stage antigens of Plasmodium falciparum in rural Gambians and their relation to protection against infection.

Abstract: Cross-sectional and longitudinal studies were performed in a rural population living in The Gambia to examine the relationship between several in vitro assays of the host immune response to asexual stages of Plasmodium falciparum and protection from malaria in vivo. Assays included an enzyme-linked immunosorbent assay for antibodies to schizont antigens; an indirect immunofluorescence assay for total antiblood-stage antibodies; an immunofluorescence assay on glutaraldehyde-fixed parasites to detect antibodies to antigen Pf 155; an assay for serum inhibition of red blood cell invasion; a micro-agglutination assay to detect antibodies to neo-antigens on the surface of infected red blood cells; and an assay using polymorphonuclear leucocytes to detect antibodies capable of opsonizing schizont infected red blood cells. There were marked differences in the age-related pattern of response for different assays performed on sera obtained at a cross-sectional survey of 280 individuals. Examination of the correlation between the various immune responses and malariometric indices at the population level and at the individual level provided no evidence that any of the in vitro assays were related to protective immunity. The relationship between in vitro measurements of the anti-malarial immune response and protection from clinical episodes of malaria was examined in a group of 134 children aged 11 years and under who were monitored weekly throughout an entire malaria transmission season. The only immune factor to show a consistent protective effect against clinical malaria was the titre of antibodies to neo-antigens on the infected erythrocyte surface (P = 0.01). The same longitudinal techniques were used to examine the effect of two non-immunological factors, sickle cell trait and mosquito net usage, both of which showed significant protection against clinical episodes and malaria.

Model for signal sequence recognition from amino-acid sequence of 54K subunit of signal recognition particle

Abstract: PROTEIN targeting to the endoplasmic reticulum in mammalian cells is catalysed by signal recognition particle (SRP)1,2. Cross-linking experiments have shown that the subunit of relative molecular mass 54,000 (Mr 54K; SRP54) interacts directly with signal sequences as they emerge from the ribosome3,4. Here we present the sequence of a complementary DNA clone of SRP54 which predicts a protein that contains a putative GTP-binding domain and an unusually methionine-rich domain. The properties of this latter domain suggest that it contains the signal sequence binding site. A previously uncharacterized Escherichia coli protein has strong homology to both domains. Closely homologous GTP-binding domains are also found in the α-subunit of the SRP receptor (SRα, docking protein) in the endoplasmic reticulum membrane5-8 and in a second E. coli protein, ftsY, which resembles SRα. Recent work has shown that SRα is a GTP-binding protein and that GTP is required for the release of SRP from the signal sequence and the ribosome on targeting to the endoplasmic reticulum membrane9. We propose that SRP54 and SRα use GTP in sequential steps of the targeting reaction and that essential features of such a pathway are conserved from bacteria to mammals.

Human immunodeficiency virus 1 tat protein binds trans-activation-responsive region (TAR) RNA in vitro

Abstract: tat, the trans-activator protein for human immunodeficiency virus 1 (HIV-1), has been expressed in Escherichia coli from synthetic genes. Purified tat binds specifically to HIV-1 trans-activation-responsive region (TAR) RNA in gel-retardation, filter-binding, and immunoprecipitation assays. tat does not bind detectably to antisense TAR RNA sequences, cellular mRNA sequences, variant TAR RNA sequences with altered stem-loop structures, or TAR DNA.

Right Hemisphere and Verbal Communication

Abstract: This text provides a critical review of the questions as well as the data pertaining to the contribution of the right "non-dominant" hemisphere to verbal communication.

Association of parathyroid tumors in multiple endocrine neoplasia type 1 with loss of alleles on chromosome 11.

Abstract: Familial multiple endocrine neoplasia type 1 (MEN-1) is an autosomal dominant disorder characterized by the combined occurrence of tumors of the parathyroid glands, the pancreas, and the pituitary gland. Pancreatic tumors have previously been shown to be associated with the loss of alleles on chromosome 11; we therefore looked for similar genetic alterations in specimens of parathyroid tumors, which are the most common feature of MEN-1. We obtained parathyroid tumors and peripheral-blood leukocytes from six patients with MEN-1; 18 cloned human DNA sequences from chromosome 11 were then used to identify restriction-fragment-length polymorphisms. A loss of heterozygosity was detected in parathyroid tumors from three of the six patients with MEN-1; this finding demonstrated that allelic deletions on chromosome 11 are involved in the monoclonal development of parathyroid tumors in patients with MEN-1. In addition, studies of three affected families (with 17 affected members and 51 unaffected members) established linkage with the oncogene INT2 (peak lod score, 3.30, at 0 percent recombination); the MEN-1 gene was thus mapped to the pericentromeric region of the long arm of chromosome 11 (11q13). Our location of the MEN-1 gene at 11q13 is close to the location previously reported. We conclude that a single inherited locus on chromosome 11, band q13, causes MEN-1 and that the monoclonal development of parathyroid and pancreatic tumors in patients with MEN-1 involves similar allelic deletions on chromosome 11.

Human major histocompatibility complex contains genes for the major heat shock protein HSP70

Abstract: Little is known as to why a large number of human diseases are influenced by the major histocompatibility complex. In some cases, a direct involvement of the products of the polymorphic class I and class II, aas well as the less variable products of the class III, genes has been proposed. During characterization of the class III region for the presence of additional loci, we have located a duplicated locus encoding the major heat shock protein HSP70 between the complement and tumor necrosis factor genes. The HSP70 loci are 12 kilobases apart and lie 92 kilobases telomeric of the C2 gene. As HSP70 proteins have been linked with a protective role during and after cellular stress, and HSP70 analogues are often presented as antigens in bacterial and protozoal infections, this finding may have major implications with regard to the major histo-compatibility complex and associated diseases.

Primary stimulation by dendritic cells induces antiviral proliferative and cytotoxic T cell responses in vitro.

Abstract: We used well-gassed hanging drop (20 microliters) cultures with high concentrations of purified T cells from normal BALB/c mice to examine whether dendritic cells (DC) can induce primary antiviral proliferative T cell responses and generate virus-specific CTL We found that DC exposed to infectious influenza virus in vitro or in vivo in small numbers (01-1%) resulted in strong proliferation of responder T cells within 3 d, and this was strongly inhibited by antibodies to class II MHC molecules In addition, in 5-d cultures, the influenza-treated DC generated CTL specifically able to lyse influenza-infected syngeneic target cells bearing MHC class I antigens The most potent nucleoprotein (NP) epitope recognized by BALB/c CTL is peptide 147-158 (Arg156-) and influenza-infected DC in vitro stimulated CTL recognizing this peptide, thus mimicking the response in mice primed by intranasal influenza infection We also induced T cell proliferation and virus-specific CTL in cultures of normal T cells by stimulating with DC pulsed with the natural NP sequence 147-158 or the potent peptide 147-158 (Arg156-) Small numbers of peritoneal exudate cells, after activation with Con A to produce class II MHC expression and after removal of DC with a specific mAb (33DI), did not lead to primary CTL generation but initiated secondary stimulation in vitro Our results using the hanging drop culture method and DC as APC have implications for studying the T cell repertoire for viral components in humans without the necessity of previous immunization

The Initial Physical Damage Produced by Ionizing Radiations

Abstract: SummaryBiophysical studies of different ionizing radiations and their differences in biological effect can provide useful information and constraints on the nature of the initial biologically relevant damage and hence the subsequent biochemistry and repair processes. It is clear that the nature of the predominant critical component produced by densely ionizing (high-LET) radiations is qualitatively, as well as quantitatively, different from that which predominates for low-LET radiations. Comparisons of radiation track structure with observed biological effects of the radiations allow hypotheses to be developed as to the nature of these different types of damage. That associated with low-LET radiations seems consistent with what is known about DNA double-strand breaks (dsb). It is produced predominantly by a localized cluster of ionizations within a single electron ‘track end’ either by direct action on the DNA or in conjunction with closely-associated molecules. The characteristic high-LET damage is somew...

New regression equations for predicting peak expiratory flow in adults.

Abstract: An earlier study of peak expiratory flow (PEF) in normal adults contained too few men aged over 55 and women aged over 65 for the regression equations to be used for prediction in older people. A subsequent study was therefore carried out on an additional 23 men and 29 women aged 55 or over who were lifelong non-smokers and satisfied the same strict criteria of normality that had been used in the original study. The data from both studies were combined and a new model used to calculate equations for the regression of PEF on age and height in the two sexes. With this model predicted values could be derived for men and women aged between 15 and 85. These new equations gave predicted values in men and women aged less than 55 and 65, respectively, which were almost identical with those reported previously. The new regression equations for PEF enable values to be predicted for people aged 15-85 and so enhance the accuracy of testing in the elderly.

Construction and characterization of a herpes simplex virus type 1 mutant unable to transinduce immediate-early gene expression.

Abstract: A herpes simplex virus mutant, in1814, possessing a 12-base-pair insertion in the gene encoding the transinducing factor Vmw65 has been constructed. The insertion abolished the ability of Vmw65 to transinduce immediate-early (IE) gene expression and to form a protein-DNA complex with cell proteins and the IE-specific regulatory element TAATGAGAT. Accumulation of IE RNA 1 and 2 was reduced four- to fivefold in in1814-infected cells, but the level of IE RNA 4 was reduced only by twofold, and IE RNA 3 was unaffected. Mutant in1814 had a high particle/PFU ratio, but many of the particles, although unable to form plaques, were capable of normal participation in the early stages of infection at high multiplicity of infection. The defect of in1814 was overcome partially by transfection of a plasmid encoding the IE protein Vmw110 into cells prior to titration and by prior infection with ultraviolet light-inactivated herpes simplex virus. Mutant in1814 was essentially avirulent when injected into mice. The results demonstrate that transinduction of IE transcription by Vmw65 is important at low multiplicity of infection and in vivo but that at high multiplicity of infection the function is redundant.

Fluorescent lighting, headaches and eyestrain

Abstract: The weekly incidence of headaches among office workers was compared when the offices were lit by fluorescent lighting where the fluorescent tubes were operated by (a) a conventional switch-start ci...

Tumour necrosis factor production in Falciparum malaria and its association with schizont rupture.

Abstract: To investigate the involvement of tumour necrosis factor (TNF) in human malaria, we studied TNF production in patients infected with Plasmodium falciparum, and in co-cultures of human mononuclear cells and malaria parasites in vitro In the examined sample, plasma TNF levels of over 39 pg/ml were detected in the plasma of 59% of Gambian children with acute malaria, 17% of convalescents, 9% of children with mild infections other than malaria, and 7% of healthy Gambian adults Mononuclear cells of acute malaria patients, when stimulated with endotoxin in vitro, secreted twice as much TNF as did those of convalescent individuals, and three times that of healthy adult controls Erythrocytic cultures of P falciparum stimulated increased TNF secretion by mononuclear cells from uninfected individuals, and a sharp rise in the rate of secretion occurred shortly after schizont rupture We suggest that malaria fever is mediated, at least in part, through paroxysmal TNF release associated with schizont rupture

Colorectal cancer and diet in an asian population—A case-control study among Singapore Chinese

Abstract: A hospital-based case-control study of diet and colorectal cancer was conducted among Chinese in Singapore (who constitute 77% of the population). A total of 203 cases and 425 controls were included. A history of the usual dietary intake one year prior to interview was taken using a quantitative food frequency questionnaire. Daily intakes of nutrients and selected food items were computed and stratified by tertiles of the control range, to assess risk in low-, medium- and high-intake categories. Effects were adjusted in analysis for age, sex, Chinese dialect group and occupation. For cancers of colon and rectum combined, significant observations were a protective effect of high cruciferous vegetable intake (OR = 0.50, p less than 0.01) and a predisposing effect of a high meat/vegetable consumption ratio (OR = 1.77, p less than 0.05). Similar results were observed for colon cancer alone. For rectal cancer alone (only 71 cases), significant (p less than 0.05) protective effects were observed for high intakes of protein (OR = 0.61), fibre (OR = 0.46), beta-carotene (OR = 0.54), cruciferous vegetables (OR = 0.51) and total vegetables (OR = 0.51). When further assessed by multiple logistic regression, tests for trend and assessment of risk in the extreme highest and lowest quintiles of the control range, the factors consistently significant were cruciferous vegetable intake and the meat/vegetable ratio. A particularly high relative risk was also noted in association with low coffee consumption (OR = 1.59, with p less than 0.05 for trend). No consistent trends were noted for fat or fibre intakes. For non-dietary variables investigated, a history of cholecystectomy increased the risk of both cancers combined (OR = 3.43, p less than 0.05) and colon cancer alone (OR = 4.39, p less than 0.01). This study in an Asian population of countries of Southern and Eastern Asia newly undergoing industrialization and in which rapid economic change is reflected in changing cancer patterns, suggests that the protective effects of certain dietary constituents, notably the cruciferous vegetables, may be more important than the hitherto stressed carcinogenic potential of fat and protein.

Track structure analysis of ultrasoft X-rays compared to high- and low-LET radiations.

Abstract: SummaryMonte-Carlo track structure simulations of ultrasoft X-rays, and of selected low- and high-LET radiations for comparison, have been used to obtain statistically valid frequency distributions of energy deposition in small subcellular targets which resemble the dimensions of short segments of DNA, nucleosomes and short segments of chromatin fibre. It is found that in all cases large numbers (∼ 103) of direct energy deposition events occur in these targets in a single mammalian cell irradiated with 1 Gy of any of these radiations. In almost all cases the numbers of energy depositions of substantial size (say, ≳ 100 eV in a DNA segment, ≳ 300 eV in a nucleosome or ≳ 800 eV in a segment of chromatin fibre) are also quite large, being ∼ 10 to 100 per cell per Gy. It seems clear therefore that the direct effects of radiation on macromolecules must be considered in assessing the biological effects of any ionizing radiations on mammalian cells. The calculations also show that high-LET radiations can produce...

On the statistical analysis of ROC curves

Abstract: We introduce a new accuracy index for receiver operating characteristic (ROC) curves, namely the partial area under the binormal ROC graph over any specified region of interest. We propose a simple but general procedure, based on a conventional analysis of variance, for comparing accuracy indices derived from two or more different modalities. The proposed method is related to and compared with existing methodology, and is illustrated by results from an experiment on optimization of density and contrast yielded by multiform photographic images used for scintigraphy.

On fully automatic feature measurement for banded chromosome classification.

Abstract: Procedures for fully automatic location of chromosome axis and centromere in metaphase chromosomes are described for a practical interactive chromosome analysis system that omits the usual stages of interactive axis and centromere correction. Accuracy of centromere finding and consequential determination of a chromosome's polarity, i.e., which end is which, is measured experimentally. The saving in interaction by not correcting centromeres is compared to the increase in errors at the classification stage and the consequent increase in interaction needed to correct these errors. Some previously unreported features for banded chromosome classification are described, and in particular a set of global shape features is introduced. The discrimination capability of the feature measurements is evaluated by use of simple statistics and by reference to the performance of classifiers trained with various feature subsets. Class discrimination capability of the global shape feature set is shown to be comparable to that of centromere position, a widely used local shape feature. The variability of feature measurements that might occur in data from different laboratories on account of differing tissue, preparation methods, and digitiser hardware is assessed using three data bases of G-banded human metaphase cells. It is shown that the differences can be considerable and that appropriate feature selection and classifier training substantially improve classification performance.

Detection of high‐risk groups and individuals for periodontal diseases:

Abstract: Gingival crevicular fluid is regarded as a promising medium for the detection of markers of periodontal diseases activity. The collection protocols are straight forward and non-invasive and can be performed at specific sites of interest in the periodontium. Because the fluid accumulates at the gingival margin, it will contain potential markers derived not only from the host tissues and serum but also the subgingival microbial plaque, and thus an extremely broad range of candidate molecules may be investigated. However, the ability to successfully describe indicators of current disease activity and predictors of future disease is dependent not only upon the choice of the biochemical marker but also on the accurate description of the health status of the sample sites using currently available clinical and radiographic methods. Areas of study which currently show the most promise involve the analysis of host enzyme activities directed against components of the extracellular matrix, the nature of the glycosaminoglycans released into the sulcus and the concentration in gingival crevicular fluid of certain mediators of the inflammatory process, most notably prostaglandin E2.

Postoperative radiotherapy and late mortality: evidence from the Cancer Research Campaign trial for early breast cancer.

Abstract: OBJECTIVE--To identify any excess mortality caused by adjuvant radiotherapy for early breast cancer. DESIGN--Prospective randomised clinical trial. Two thousand subjects needed for study to have a 90% chance of detecting a difference in survival rate of 7% with 95% significance. Patients were followed up until June 1988, giving follow up of 158-216 months. SETTING--A multicentre trial mainly drawing patients from centres in the United Kingdom. PATIENTS--2800 Women presenting with clinical stage I or II carcinoma of the breast from June 1970 to April 1975. INTERVENTIONS--One group of women (n = 1376) had simple mastectomy followed by immediate postoperative radiotherapy (1320 to 1510 rets). The remaining women (n = 1424) had simple mastectomy with subsequent careful observation of the axilla, radiotherapy being delayed until there was obvious progression or recurrence of disease locally. END POINT--Increased mortality in patients treated with radiotherapy from causes other than breast cancer. MEASUREMENTS AND MAIN RESULTS--Survival was measured from time of first treatment to death or last follow up. Deaths from any cause and from specified causes were counted as events. Comparison over the whole follow up showed a slight excess mortality in the group treated with radiotherapy (relative risk 1.04; 95% confidence interval 0.94 to 1.15). The relative risk of death from breast cancer was 0.97 (0.87 to 1.08) but that of death from other causes was 1.37 (1.09 to 1.72), the increase mainly being in women who had had tumours of the left breast (1.61 (1.17 to 2.24)) and had been treated with orthovoltage (1.85 (1.27 to 2.71)). Analysis of causes of death after five years showed a relative risk of 2.11 (1.25 to 3.59) for new malignancies and of 1.65 (1.05 to 2.58) for cardiac disease, the increase in cardiac mortality being most pronounced in patients who had had tumours of the left breast and whose treatment had included orthovoltage radiation (relative risk 2.67 (1.28 to 5.55)). CONCLUSIONS--Adjuvant radiotherapy after simple mastectomy for early breast cancer produces a small excess late mortality from other cancers and cardiac disease. The risk has to be balanced against the higher risk of local recurrence when immediate postoperative radiotherapy is not given. The balance has to be assessed for each patient, and for many patients radiotherapy will still be desirable in the initial treatment of their early breast cancer.

The MTT assay underestimates the growth inhibitory effects of interferons.

Abstract: The growth inhibitory effects of interferons, IFN-alpha and IFN-gamma on human lung cancer cell lines were studied using both a tetrazolium (MTT) colorimetric assay and direct cell counting. Significant discrepancies between the two assays were observed, the MTT assay consistently underestimating the growth inhibitory effects of the IFNs. There was no direct chemical effect of the IFNs on the tetrazolium reduction process. IFN treated cells showed increased cell size compared with control cells, although there was little or no change in cell cycle distribution. Mitochondrial activity was 30-50% greater in IFN-gamma treated cells (COR-L23) than the controls. Reduced formazan production per cell was observed in medium which had supported cell growth for several days. Differential 'medium conditioning' led to a difference in formazan production per cell between IFN and control cells and this was the major basis of the observed discrepancy. This discrepancy was not due to the differences in the glucose concentrations between these media. However, differences in pH between the media proved to be the major contributory factor of the discrepancy.

3. Impact of culture and environmental changes on epidemiology and control of malaria and babesiosis. The microepidemiology of malaria and its importance to malaria control

Abstract: Recent studies in West Africa and in Papua New Guinea have shown that the prevalence of malaria can vary widely between neighbouring villages and within different parts of the same village. Both genetic and environmental factors are likely to contribute to these variations. Clustering in households of genetically determined red cell abnormalities, and possibly of immune response genes, may contribute to differences in the prevalence of malaria within a village. Environmental factors probably play the major part in explaining differences between villages. The position of a village in relation to mosquito breeding sites, die design of houses and the level at which anti-mosquito measures are used will all influence the degree to which its inhabitants are exposed to infection. Attitudes to the treatment of a case of malaria may also contribute to local variations in the prevalence of malaria. Malaria parasitaemia and splenomegaly will be less frequent in a community where effective treatment is given immediately at home, or sought promptly from a primary health care worker, than in a neighbouring community where there is a much greater reliance on traditional medicines. Recognition of local variations in the prevalence of malaria is important because identification of the factors responsible for a low prevalence in one village but a high one in a neighbouring community may indicate a possible control measure. Local variations in the epidemiology of malaria must also be taken into account when any kind of malaria intervention trial is planned.

The effects of malaria chemoprophylaxis given by traditional birth attendants on the course and outcome of pregnancy.

Abstract: A trial of malaria chemoprophylaxis given by traditional birth attendants was undertaken in a rural area of The Gambia where access to antenatal clinics is difficult. Women received one or more doses of Maloprim or placebo from a traditional birth attendant during 1049 of 1208 pregnancies (87%) recorded in 16 villages over a 3-year period. Primigravidae who received Maloprim had a lower parasite rate and a significantly higher mean packed cell volume than primigravidae who received placebo, and their babies were significantly heavier (6% low birth weight vs 22%). In multigravidae chemoprophylaxis reduced malaria parasitaemia but it had no beneficial effect on haemoglobin level and much less effect on birth weight than was observed in primigravidae. However, the mean birth weight of babies born to grandemultigravidae who received chemoprophylaxis was significantly higher than that of babies born to grandemultigravidae who did not.

Regulation of cell cycle duration by c-myc levels

Abstract: Early passage murine fibroblasts infected with retroviral vectors carrying human c-myc 'minigenes' express high levels of c-myc and have a dramatically shortened G1-phase of the cell cycle. Cells infected with viruses where c-myc is expressed from the viral LTR (MSN-4 virus) express more c-myc protein than cells infected with viruses where c-myc is expressed from the SV40 early promoter (NSM-7 virus). Populations of cells were infected with high titre viruses, selected for drug-resistance, pulse labelled with bromodeoxyuridine (BrdUrd) and chased in BrdUrd free media. This allows accurate, simultaneous, measurement of the rate of exit of unlabelled cells from G1 and progression of BrdUrd-labelled cells through S-phase. The length of the G1-phase in cell populations infected with the MSN-4 virus is 4.65 h, a reduction of nearly 30% compared to the G1-phase length of 6.50 h seen in cells infected with the VSN-2 control virus. Cells infected with NSM-7 virus show an intermediate phenotype and have a G1-phase of 5.25 h. The lengths of the S-phase (4.50 to 4.75 h) and G2 + M phases (2.75 h) were not significantly altered by exogenous c-myc expression. When chases are performed in growth-factor free media, the G1-phase of infected and non-infected cells is extended by approximately 2 h. Cells infected with the c-myc viruses continue to cycle more rapidly than uninfected cells. Growth factor-deprived cells, restimulated with serum, show similar alterations of the cell cycle kinetics. MSN-4 and NSM-7 infected cells, expressing high levels of c-myc, enter S-phase 2 to 4 h earlier, but less synchronously, than control cells, and sustain subsequent rounds of DNA synthesis, while control cells do not. However, cells carrying activated c-myc genes have nearly-normal morphologies and are not tumourgenic in syngenic mice. These results demonstrate that c-myc levels are rate limiting for events in G1, and the length of G1 varies proportionally with the level of exogenous c-myc expression.

Febrile temperatures can synchronize the growth of Plasmodium falciparum in vitro.

Abstract: To investigate the possibility that the host fever response in malaria may affect parasite development, we studied the effect of temperature on Plasmodium falciparum in erythrocytic culture in vitro. Growth was markedly suppressed at 40 degrees C compared with 37 degrees C, due to disruption of the second half of the 48-h erythrocytic cycle. However, young intraerythrocytic parasites, which are highly exposed to fever during natural infection, appeared to develop normally at 40 degrees C. Because of the differential temperature sensitivity within the erythrocytic cycle, asynchronous cultures could be synchronized by transient elevations of temperature. Pronounced synchronization was observed when cultures were exposed to periodic elevations of temperature that simulated the 48-h fever cycle of tertian malaria. These findings indicate that malaria fever might act to promote parasite synchronization in vivo.