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PubMed2003

Tritrophic choice experiments with bt plants, the diamondback moth (Plutella xylostella) and the parasitoid Cotesia plutellae.

Parasitoids are important natural enemies of many pest species and are used extensively in biological and integrated control programmes. Crop plants transformed to express toxin genes derived from Bacillus thuringiensis (Bt) provide high levels of resistance to certain pest species, which is likely to have consequent effects on parasitoids specialising on such pests. A better understanding of the interaction between transgenic plants, pests and parasitoids is important to limit disruption of biological control and to provide background knowledge essential for implementing measures for the conservation of parasitoid populations. It is also essential for investigations into the potential role of parasitoids in delaying the build-up of Bt-resistant pest populations. The diamondback moth (Plutella xylostella), a major pest of brassica crops, is normally highly susceptible to a range of Bt toxins. However, extensive use of microbial Bt sprays has led to the selection of resistance to Bt toxins in P. xylostella. Cotesia plutellae is an important endoparasitoid of P. xylostella larvae. Although unable to survive in Bt-susceptible P. xylostella larvae on highly resistant Bt oilseed rape plants due to premature host mortality, C. plutellae is able to complete its larval development in Bt-resistant P. xylostella larvae. Experiments of parasitoid flight and foraging behaviour presented in this paper showed that adult C. plutellae females do not distinguish between Bt and wildtype oilseed rape plants, and are more attracted to Bt plants damaged by Bt-resistant hosts than by susceptible hosts. This stronger attraction to Bt plants damaged by resistant hosts was due to more extensive feeding damage. Population scale experiments with mixtures of Bt and wildtype plants demonstrated that the parasitoid is as effective in controlling Bt-resistant P. xylostella larvae on Bt plants as on wildtype plants. In these experiments equal or higher numbers of parasitoid adults emerged per transgenic as per wildtype plant. The implications for integrated pest management and the evolution of resistance to Bt in P. xylostella are discussed.

Animals↗
PubMed2006

Gene expression profiling of Spodoptera frugiperda hemocytes and fat body using cDNA microarray reveals polydnavirus-associated variations in lepidopteran host genes transcript levels.

BACKGROUND: Genomic approaches provide unique opportunities to study interactions of insects with their pathogens. We developed a cDNA microarray to analyze the gene transcription profile of the lepidopteran pest Spodoptera frugiperda in response to injection of the polydnavirus HdIV associated with the ichneumonid wasp Hyposoter didymator. Polydnaviruses are associated with parasitic ichneumonoid wasps and are required for their development within the lepidopteran host, in which they act as potent immunosuppressive pathogens. In this study, we analyzed transcriptional variations in the two main effectors of the insect immune response, the hemocytes and the fat body, after injection of filter-purified HdIV. RESULTS: Results show that 24 hours post-injection, about 4% of the 1750 arrayed host genes display changes in their transcript levels with a large proportion (76%) showing a decrease. As a comparison, in S. frugiperda fat body, after injection of the pathogenic JcDNV densovirus, 8 genes display significant changes in their transcript level. They differ from the 7 affected by HdIV and, as opposed to HdIV injection, are all up-regulated. Interestingly, several of the genes that are modulated by HdIV injection have been shown to be involved in lepidopteran innate immunity. Levels of transcripts related to calreticulin, prophenoloxidase-activating enzyme, immulectin-2 and a novel lepidopteran scavenger receptor are decreased in hemocytes of HdIV-injected caterpillars. This was confirmed by quantitative RT-PCR analysis but not observed after injection of heat-inactivated HdIV. Conversely, an increased level of transcripts was found for a galactose-binding lectin and, surprisingly, for the prophenoloxidase subunits. The results obtained suggest that HdIV injection affects transcript levels of genes encoding different components of the host immune response (non-self recognition, humoral and cellular responses). CONCLUSION: This analysis of the host-polydnavirus interactions by a microarray approach indicates that the presence of HdIV induces, directly or indirectly, variations in transcript levels of specific host genes, changes that could be responsible in part for the alterations observed in the parasitized host physiology. Development of such global approaches will allow a better understanding of the strategies employed by parasites to manipulate their host physiology, and will permit the identification of potential targets of the immunosuppressive polydnaviruses.

Animals↗
PubMed1998

An analysis of the geographical distribution of severe malaria in children in Kilifi District, Kenya.

BACKGROUND: Although malaria is known to be a major cause of child mortality and morbidity throughout sub-Saharan Africa there are few detailed studies of malaria mortality rates and incidence of severe malarial disease in defined communities. We have studied the geographical pattern of admissions to hospital with severe malaria and the stability of this pattern over time in Kilifi District on the Kenyan Coast. METHODS: Over a 2-year period all children under 5 years of age with severe malaria admitted to the district hospital and living in a rural study population of about 50,000 people were identified. Annual censuses were carried out in the study area, and all households were mapped using a hand-held satellite navigation system. The resulting databases were linked using a geographical information system (GIS). RESULTS: Using methods originally developed for the study of the geographical distribution of childhood leukaemia we assessed the spatial pattern of hospital admission rates for severe malaria. As expected, admission rates were significantly higher in children with easier access to the hospital. For example, those living more than 25 km from the hospital had admission rates which were about one-fifth of those for children living within 5 km of the hospital. Those living more than 2.5 km from the nearest road had admission rates that were about half of those for children living within 0.5 km of a road. We also investigated short-term local fluctuations in severe malaria and found evidence of space-time clustering of severe malaria. CONCLUSIONS: Hospital admission rates for severe malaria are higher in households with better access to hospital than in those further away. The finding of space-time clusters of severe malaria suggests that it would be of value to conduct case-control studies of environmental, genetic and human behavioural factors involved in the aetiology of the disease.

Animals↗
PubMed2004

Polymorphism of Fc receptor IIa for immunoglobulin G is associated with placental malaria in HIV-1-positive women in western Kenya.

BACKGROUND: Genetic polymorphism of the Fc receptor IIa for immunoglobulin (Ig) G (Fc gamma RIIa) determines IgG subclass binding. Previous studies have shown that individuals with the IgG1/3-binding Fc gamma RIIa-Arg/Arg131 genotype are relatively protected against high-density malaria, whereas individuals with the IgG2-binding Fc gamma RIIa-His/His131 genotype are at increased risk for developing cerebral malaria. The present study was undertaken to examine the relationship between Fc gamma RIIa polymorphism and placental malaria (PM) in pregnant women of known human immunodeficiency virus (HIV)-1 status. METHODS: Fc gamma RIIa genotype was determined in 903 pregnant women who had participated in a study designed to assess the effect that PM has on vertical transmission of HIV-1. Fc gamma RIIa polymorphism was assessed in relation to PM. RESULTS: Among HIV-negative women, there was no difference in the distribution of the Fc gamma RIIa polymorphism by PM status. However, among HIV-positive women, the frequency of the Fc gamma RIIa-His/His131 genotype was significantly higher in women with PM than in women without PM (31% vs. 22%, respectively [P=.032]). In multivariate analysis, the adjusted odds ratio for PM in HIV-positive women with the Fc gamma RIIa-His/His131 genotype versus women in the Fc gamma RIIa-His/Arg131 reference group was 1.72 (95% confidence interval, 1.11-2.69 [P=.016]). CONCLUSIONS: The present study suggests that the IgG2-binding Fc gamma RIIa-His/His131 genotype is associated with enhanced susceptibility to PM in HIV-positive women but not in HIV-negative women.

Alleles↗
PubMed2004

Optimal cDNA microarray design using expressed sequence tags for organisms with limited genomic information.

BACKGROUND: Expression microarrays are increasingly used to characterize environmental responses and host-parasite interactions for many different organisms. Probe selection for cDNA microarrays using expressed sequence tags (ESTs) is challenging due to high sequence redundancy and potential cross-hybridization between paralogous genes. In organisms with limited genomic information, like marine organisms, this challenge is even greater due to annotation uncertainty. No general tool is available for cDNA microarray probe selection for these organisms. Therefore, the goal of the design procedure described here is to select a subset of ESTs that will minimize sequence redundancy and characterize potential cross-hybridization while providing functionally representative probes. RESULTS: Sequence similarity between ESTs, quantified by the E-value of pair-wise alignment, was used as a surrogate for expected hybridization between corresponding sequences. Using this value as a measure of dissimilarity, sequence redundancy reduction was performed by hierarchical cluster analyses. The choice of how many microarray probes to retain was made based on an index developed for this research: a sequence diversity index (SDI) within a sequence diversity plot (SDP). This index tracked the decreasing within-cluster sequence diversity as the number of clusters increased. For a given stage in the agglomeration procedure, the EST having the highest similarity to all the other sequences within each cluster, the centroid EST, was selected as a microarray probe. A small dataset of ESTs from Atlantic white shrimp (Litopenaeus setiferus) was used to test this algorithm so that the detailed results could be examined. The functional representative level of the selected probes was quantified using Gene Ontology (GO) annotations. CONCLUSIONS: For organisms with limited genomic information, combining hierarchical clustering methods to analyze ESTs can yield an optimal cDNA microarray design. If biomarker discovery is the goal of the microarray experiments, the average linkage method is more effective, while single linkage is more suitable if identification of physiological mechanisms is more of interest. This general design procedure is not limited to designing single-species cDNA microarrays for marine organisms, and it can equally be applied to multiple-species microarrays of any organisms with limited genomic information.

Animals↗
PubMedDate not supplied

Mefloquine resistance in Plasmodium falciparum and increased pfmdr1 gene copy number.

BACKGROUND: The borders of Thailand harbour the world's most multidrug resistant Plasmodium falciparum parasites. In 1984 mefloquine was introduced as treatment for uncomplicated falciparum malaria, but substantial resistance developed within 6 years. A combination of artesunate with mefloquine now cures more than 95% of acute infections. For both treatment regimens, the underlying mechanisms of resistance are not known. METHODS: The relation between polymorphisms in the P falciparum multidrug resistant gene 1 (pfmdr1) and the in-vitro and in-vivo responses to mefloquine were assessed in 618 samples from patients with falciparum malaria studied prospectively over 12 years. pfmdr1 copy number was assessed by a robust real-time PCR assay. Single nucleotide polymorphisms of pfmdr1, P falciparum chloroquine resistance transporter gene (pfcrt) and P falciparum Ca2+ ATPase gene (pfATP6) were assessed by PCR-restriction fragment length polymorphism. FINDINGS: Increased copy number of pfmdr1 was the most important determinant of in-vitro and in-vivo resistance to mefloquine, and also to reduced artesunate sensitivity in vitro. In a Cox regression model with control for known confounders, increased pfmdr1 copy number was associated with an attributable hazard ratio (AHR) for treatment failure of 6.3 (95% CI 2.9-13.8, p<0.001) after mefloquine monotherapy and 5.4 (2.0-14.6, p=0.001) after artesunate-mefloquine therapy. Single nucleotide polymorphisms in pfmdr1 were associated with increased mefloquine susceptibility in vitro, but not in vivo. INTERPRETATION: Amplification in pfmdr1 is the main cause of resistance to mefloquine in falciparum malaria. RELEVANCE TO PRACTICE: Multidrug resistant P falciparum malaria is common in southeast Asia, but difficult to identify and treat. Genes that encode parasite transport proteins maybe involved in export of drugs and so cause resistance. In this study we show that increase in copy number of pfmdr1, a gene encoding a parasite transport protein, is the best overall predictor of treatment failure with mefloquine. Increase in pfmdr1 copy number predicts failure even after chemotherapy with the highly effective combination of mefloquine and 3 days' artesunate. Monitoring of pfmdr1 copy number will be useful in epidemiological surveys of drug resistance in P falciparum, and potentially for predicting treatment failure in individual patients.

ATP-Binding Cassette Transporters↗
PubMed2002

Complexities in ETS-domain transcription factor function and regulation: lessons from the TCF (ternary complex factor) subfamily. The Colworth Medal Lecture.

The ETS-domain transcription factor family can be divided into a series of subfamilies. Elk-1 represents the founding member of the ternary complex factor (TCF) subfamily. By focusing on the TCF subfamily, we can demonstrate the complexities that exist in the function and regulation of ETS-domain transcription factors. This article focuses on Elk-1 in detail and summarizes the functions of other TCFs. The key themes covered include the domain structure of the TCFs, the mechanisms of complex formation with serum response factor, regulation of TCFs by mitogen-activated protein kinase cascades, and transcriptional regulatory properties of the TCFs. Finally, the emerging role of the TCFs in vivo is discussed. A picture is developing indicating that, while these proteins exhibit significant sequence and functional conservation, key differences in their structure and regulation are being identified which may relate to unique functions of these proteins in vivo.

Amino Acid Sequence↗