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Search Results: 1 - 10 of 229170 matches for " Simon C Harvey "
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All Eggs Are Not Equal: The Maternal Environment Affects Progeny Reproduction and Developmental Fate in Caenorhabditis elegans
Simon C. Harvey, Helen E. Orbidans
PLOS ONE , 2011, DOI: 10.1371/journal.pone.0025840
Abstract: Background Maternal effects on progeny traits are common and these can profoundly alter progeny life history. Maternal effects can be adaptive, representing attempts to appropriately match offspring phenotype to the expected environment and are often mediated via trade-offs between progeny number and quality. Here we have investigated the effect of maternal food availability on progeny life history in the free-living nematode Caenorhabditis elegans. Methodology/Principal Findings The maternal environment affects both reproductive traits and progeny development. Comparisons of the progeny of worms from high and low maternal food environments indicates that low maternal food availability reduces progeny reproduction in good environments, increases progeny reproduction in poor environments and decreases the likelihood that progeny will develop as dauer larvae. These analyses also indicate that the effects on progeny are not a simple consequence of changes in maternal body size, but are associated with an increase in the size of eggs produced by worms at low maternal food availabilities. Conclusions/Significance These results indicate that the maternal environment affects both progeny reproduction and development in C. elegans and therefore that all progeny are not equal. The observed effects are consistent with changes to egg provisioning, which are beneficial in harsh environments, and of changes to progeny development, which are beneficial in harsh environments and detrimental in benign environments. These changes in progeny life history suggest that mothers in poor quality environments may be producing larger eggs that are better suited to poor conditions.
Quantitative genetic analysis of life-history traits of Caenorhabditis elegans in stressful environments
Simon C Harvey, Alison Shorto, Mark E Viney
BMC Evolutionary Biology , 2008, DOI: 10.1186/1471-2148-8-15
Abstract: We found that lines of C. elegans vary in their phenotypic plasticity of dauer larva development, i.e. there is variation in the likelihood of developing into a dauer larva for the same environmental change. There was also variation in how lifetime fecundity and the rate of reproduction changed under conditions of environmental stress. These traits were related, such that lines that are highly plastic for dauer larva development also maintain a high population growth rate when stressed. We identified quantitative trait loci (QTL) on two chromosomes that control the dauer larva development and population size phenotypes. The QTLs affecting the dauer larva development and population size phenotypes on chromosome II are closely linked, but are genetically separable. This chromosome II QTL controlling dauer larva development does not encompass any loci previously identified to control dauer larva development. This chromosome II region contains many predicted 7-transmembrane receptors. Such proteins are often involved in information transduction, which is clearly relevant to the control of dauer larva development.C. elegans alters both its larval development and adult reproductive strategy in response to environmental stress. Together the phenotypic and genotypic data suggest that these two major life-history traits are co-ordinated responses to environmental stress and that they are, at least in part, controlled by the same genomic regions.Organisms live in environments that vary both spatially and temporally. In such variable environments there are different ways to maximise fitness. Life-history traits can either be robust to environmental change (a buffered or canalised trait) or they can be variable in an environmentally-dependent manner (a phenotypically plastic trait). Phenotypic plasticity of a trait can be manifest as a continuous phenotypic range across an environmental gradient, such as the variation in Drosophila melanogaster body size metrics across temperat
Quantitative genetic analysis of life-history traits of Caenorhabditis elegans in stressful environments
Simon C Harvey, Alison Shorto, Mark E Viney
BMC Evolutionary Biology , 2009, DOI: 10.1186/1471-2148-9-96
Abstract: In Figure 1 of [1] the plotted data were inverted. The correct Figure is shown below. The text and statistical analyses in [1] are correct.
Natural variation in gene expression in the early development of dauer larvae of Caenorhabditis elegans
Simon C Harvey, Gary LA Barker, Alison Shorto, Mark E Viney
BMC Genomics , 2009, DOI: 10.1186/1471-2164-10-325
Abstract: There were substantial transcriptional differences between four C. elegans lines under the same environmental conditions. The expression of approximately 2,000 genes differed between genetically different lines, with each line showing a largely line-specific transcriptional profile. The expression of genes that are markers of larval moulting suggested that the lines may be developing at different rates. The expression of a total of 89 genes was putatively affected by dauer larva or non-dauer larva-inducing conditions. Among the upstream regions of these genes there was an over-representation of DAF-16-binding motifs.Under the same environmental conditions genetically different lines of C. elegans had substantial transcriptional differences. This variation may be due to differences in the developmental rates of the lines. Different environmental conditions had a rather smaller effect on transcription. The preponderance of DAF-16-binding motifs upstream of these genes was consistent with these genes playing a key role in the decision between development into dauer or into non-dauer larvae. There was little overlap between the genes whose expression was affected by environmental conditions and previously identified loci involved in the plasticity of dauer larva development.Developmental decisions and processes can be controlled transcriptionally. The free-living nematode Caenorhabditis elegans makes a developmental decision between different larval fates. This decision is based on the 'suitability' of the environment for growth and reproduction. Under 'favourable' conditions, second stage larvae (L2) develop via two larval stages (L3, L4) into reproductive adults [1,2]. However, under 'unfavourable' conditions, L2s form a developmentally arrested L3 stage, the so-called dauer larva. Dauer larvae are environmentally resistant, have a specialised metabolism and are comparatively long-lived [2]. Overall, dauer larvae are transcriptionally repressed compared with actively
Chronic fatigue syndrome: identifying zebras amongst the horses
Samuel B Harvey, Simon Wessely
BMC Medicine , 2009, DOI: 10.1186/1741-7015-7-58
Abstract: See the associated research paper by Jones et al: http://www.biomedcentral.com/1741-7015/7/57 webciteMedical students are often told that the sound of approaching hooves is more likely to herald the arrival of horses than zebras. The metaphor reinforces the idea that in medicine common things happen commonly and that clinicians should avoid spending too much time chasing rare or unlikely diagnoses. Fatigue is a very common clinical problem with many possible causes [1,2]. Some causes of fatigue are common 'horses' such as anaemia, viral infections, sleep deprivation, diabetes and depression. However, potential 'zebras' such as malignancy or auto-immune disorders may also present with fatigue. Even with extensive investigations, the underlying aetiology of an individual's fatigue in many cases remains unknown. Over recent decades there has been increasing recognition of a group of individuals with severe, persistent, and unexplained fatigue [3]. Such persistent fatigue has, at times, been seen as an illness of modern life, although there is good evidence to show that chronic fatigue has been a common problem since at least the 19th century, but under different diagnostic labels, such as neurasthenia [4,5]. Some, but by no means all, of these individuals fulfil the current criteria for chronic fatigue syndrome (CFS), which requires that persisting or relapsing fatigue be present for at least 6 months, is not relieved by rest, is not explained by medical or psychiatric conditions and is accompanied by a range of cognitive and somatic symptoms [6]. Here, we discuss a paper by Jones et al. published this month in BMC Medicine [7], as well as recent prospective studies that provide valuable insights into the aetiology and contribute to a model for understanding chronic fatigue.At present, and despite much effort, there are no investigative tools or physical signs that can confirm the presence of CFS and it remains a diagnosis of exclusion [8]. As a result, clinicians must
Validation of a maternal questionnaire on correlates of physical activity in preschool children
Alison M McMinn, Esther MF van Sluijs, Nicholas C Harvey, Cyrus Cooper, Hazel M Inskip, Keith M Godfrey, Simon J Griffin
International Journal of Behavioral Nutrition and Physical Activity , 2009, DOI: 10.1186/1479-5868-6-81
Abstract: The questionnaire was designed to measure the following constructs: child personal factors; parental support and self-efficacy for providing support; parental rules and restrictions; maternal attitudes and perceptions; maternal behaviour; barriers to physical activity; and the home and local environments. Two separate studies were conducted. Study I included 24 mothers of four-year-old children who completed the questionnaire then participated in a telephone interview covering similar items to the questionnaire. To assess validity, the agreement between interview and questionnaire responses was assessed using Cohen's kappa and percentage agreement. Study II involved 398 mothers of four-year-old children participating in the Southampton Women's Survey. In this study, principal components analysis was used to explore the factor structure of the questionnaire to aid future analyses with these data. The internal consistency of the factors identified was assessed using Cronbach's alpha.Kappa scores showed 30% of items to have moderate agreement or above, 23% to have fair agreement and 47% to have slight or poor agreement. However, 89% of items had fair agreement as assessed by percentage agreement (≥ 66%). Limited variation in responses to variables is likely to have contributed to some of the low kappa values. Six questions had a low kappa and low percentage agreement (defined as poor validity); these included questions from the child personal factors, maternal self-efficacy, rules and restrictions, and local environment domains. The principal components analysis identified eleven factors and found several variables to stand alone. Eight of the composite factors identified had acceptable internal consistency (α ≥ 0.60) and three fell just short of achieving this (0.60 > α > 0.50).Overall, this maternal questionnaire had reasonable validity and internal consistency for assessing potential correlates of physical activity in young children. With minor revision, this could
Correlates of Light and Moderate-to-Vigorous Objectively Measured Physical Activity in Four-Year-Old Children
Esther M. F. van Sluijs, Alison M. McMinn, Hazel M. Inskip, Ulf Ekelund, Keith M. Godfrey, Nicholas C. Harvey, Simon J. Griffin
PLOS ONE , 2013, DOI: 10.1371/journal.pone.0074934
Abstract: Background Correlates of physical activity (PA) are hypothesized to be context and behaviour specific, but there is limited evidence of this in young children. The aim of the current study is to investigate associations between personal, social and environmental factors and objectively measured light and moderate-to-vigorous PA (LPA and MVPA, respectively) in four-year-old children. Methods Cross-sectional data were used from the Southampton Women’s Survey, a UK population-based longitudinal study. Four-year old children (n = 487, 47.0% male) had valid PA data assessed using accelerometry (Actiheart) and exposure data collected with a validated maternal questionnaire (including data on child personality, family demographics, maternal behaviour, rules and restrictions, and perceived local environment). Linear regression modelling was used to analyse associations with LPA and MVPA separately, interactions with sex were explored. Results LPA minutes were greater in children whose mothers reported more PA (vs. inactive: regression coefficient±standard error: 6.70±2.94 minutes), and without other children in the neighbourhood to play with (?6.33±2.44). MVPA minutes were greater in children with older siblings (vs. none: 5.81±2.80) and those whose mothers used active transport for short trips (vs. inactive: 6.24±2.95). Children accumulated more MVPA in spring (vs. winter: 9.50±4.03) and, in boys only, less MVPA with availability of other children in the neighbourhood (?3.98±1.70). Discussion Young children’s LPA and MVPA have differing associations with a number of social and environmental variables. Interventions targeting PA promotion in young children outside of formal care settings should consider including intensity specific factors.
Differential Host Immune Responses after Infection with Wild-Type or Lab-Attenuated Rabies Viruses in Dogs
Clement W. Gnanadurai?,Yang Yang?,Ying Huang?,Zhenguang Li?,Christina M. Leyson?,Tanya L. Cooper?,Simon R. Platt?,Stephen B. Harvey,Douglas C. Hooper?,Milosz Faber
PLOS Neglected Tropical Diseases , 2015, DOI: 10.1371/journal.pntd.0004023
Abstract: Rabies virus (RABV) induces encephalomyelitis in humans and animals. One of the major problems with rabies is that the infected individuals most often do not develop virus neutralizing antibodies (VNA). In this study we have investigated the host immune response to RABV infection in dogs, using a live-attenuated (TriGAS) or a wild-type (wt) (DRV-NG11) RABV isolated from a rabid dog. Methodology/Principal Findings The experimental infection of dogs with TriGAS induced high levels of VNA in the serum, whereas wt RABV infection did not. Dogs infected with TriGAS developed antibodies against the virus including its glycoprotein, whereas dogs infected with DRV-NG11 only developed rabies antibodies that are presumably specific for the nucleoprotein, (N) and not the glycoprotein (G). We show that infection with TriGAS induces early activation of B cells in the draining lymph nodes and persistent activation of DCs and B cells in the blood. On the other hand, infection with DRV-NG11 fails to induce the activation of DCs and B cells and further reduces CD4 T cell production. Further, we show that intrathecal (IT) immunization of TriGAS not only induced high levels of VNA in the serum but also in the CSF while intramuscular (IM) immunization of TriGAS induced VNA only in the serum. In addition, high levels of total protein and WBC were detected in the CSF of IT immunized dogs, indicating the transient enhancement of blood-brain barrier (BBB) permeability, which is relevant to the passage of immune effectors from periphery into the CNS. Conclusions/Significance IM infection of dogs with TriGAS induced the production of serum VNA whereas, IT immunization of TriGAS in dogs induces high levels of VNA in the periphery as well as in the CSF and transiently enhances BBB permeability. In contrast, infection with wt DRV-NG11 resulted in the production of RABV-reactive antibodies but VNA and antibodies specific for G were absent. As a consequence, all of the dogs infected with wt DRV-NG11 succumbed to rabies. Thus the failure to activate protective immunity is one of the important features of RABV pathogenesis in dogs.
What Are the Economic and Labour Market Effects of an Income Tax Reduction Targeted at Older Workers?
Maxime Fougère,Simon Harvey,Bruno Rainville
Economics Research International , 2012, DOI: 10.1155/2012/461597
Abstract: This paper explores the economic and labour market effects of implementing a tax reduction targeted at older workers. The analysis is conducted with a life-cycle computable general equilibrium model calibrated on Canadian data. The analysis shows that implementing a permanent income tax reduction for workers aged 60 and over has only small macroeconomic effects because the labour supply increase of older workers is partly offset by a reduction in the labour supply at core ages. This induced effect also discourages savings and generates crowding out through private investment but has a favourable impact on lifetime economic welfare. The macroeconomic impact is much larger when the income tax reduction is temporary because workers no longer reduce their hours at core ages and there is no reduction in savings. However, since only current middle-aged and older workers benefit from the tax cut, a temporary income tax cut reduces intergenerational equity.
Would an Increase in High-Skilled Immigration in Canada Benefit Workers?
Maxime Fougère,Simon Harvey,Bruno Rainville
Economics Research International , 2011, DOI: 10.1155/2011/171927
Abstract: This study examines the economic and welfare effects of raising the number of high-skilled immigrants in Canada. It uses a life-cycle applied general equilibrium model with endogenous time allocation decisions between work, education, and leisure. According to the simulation results, raising the number of high-skilled immigrants would boost productive capacity and labour productivity but could lower real GDP per capita. In addition, by raising the supply of high-skilled workers, more high-skilled immigrants would reduce the skill premium and the return to human capital. This in turn would lower incentives for young adults to invest in human capital and have a dampening effect on the domestic supply of skilled workers. Finally, it is found that more high-skilled immigrants would be welfare enhancing for medium- and low-skilled workers but welfare decreasing for high-skilled workers.
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