Biomedical subjects

Phillip J Daborn

Publications and source records attributed to Phillip J Daborn.

10 recordsLinked to original sources

PubMed2007

Towards genetic markers in animal populations as biomonitors for human-induced environmental change.

Genetic markers provide potentially sensitive indicators of changes in environmental conditions because the genetic constitution of populations is normally altered well before populations become extinct. Genetic indicators in populations include overall genetic diversity, genetic changes in traits measured at the phenotypic level, and evolution at specific loci under selection. While overall genetic diversity has rarely been successfully related to environmental conditions, genetically based changes in traits have now been linked to the presence of toxins and both local and global temperature shifts. Candidate loci for monitoring stressors are emerging from information on how specific genes influence traits, and from screens of random loci across environmental gradients. Drosophila research suggests that chromosomal regions under recent intense selection can be identified from patterns of molecular variation and a high frequency of transposable element insertions. Allele frequency changes at candidate loci have been linked to pesticides, pollutants and climate change. Nevertheless, there are challenges in interpreting allele frequencies in populations, particularly when a large number of loci control a trait and when interactions between alleles influence trait expression. To meet these challenges, population samples should be collected for longitudinal studies, and experimental programmes should be undertaken to link variation at candidate genes to ecological processes.

Adaptation, Physiological↗

PubMed2006

Fighting fly genes.

Fighting by organisms such as mice and Drosophila provides model systems for investigating the genetic basis of aggression. Recent experiments to dissect male aggressive behaviour in Drosophila melanogaster, using gene expression analysis of selected lines followed by mutant analysis, have identified new candidate genes associated with male aggression, including one strong candidate that encodes a cytochrome P450 enzyme. Here, we describe the study of aggressive behaviour in flies and explore the possibility that cytochrome P450 is involved in aggression.

Agonistic Behavior↗

PubMed2006

Cis-regulatory elements in the Accord retrotransposon result in tissue-specific expression of the Drosophila melanogaster insecticide resistance gene Cyp6g1.

Transposable elements are a major mutation source and powerful agents of adaptive change. Some transposable element insertions in genomes increase to a high frequency because of the selective advantage the mutant phenotype provides. Cyp6g1-mediated insecticide resistance in Drosophila melanogaster is due to the upregulation of the cytochrome P450 gene Cyp6g1, leading to the resistance to a variety of insecticide classes. The upregulation of Cyp6g1 is correlated with the presence of the long terminal repeat (LTR) of an Accord retrotransposon inserted 291bp upstream of the Cyp6g1 transcription start site. This resistant allele (DDT-R) is currently at a high frequency in D. melanogaster populations around the world. Here, we characterize the spatial expression of Cyp6g1 in insecticide-resistant and -susceptible strains. We show that the Accord LTR insertion is indeed the resistance-associated mutation and demonstrate that the Accord LTR carries regulatory sequences that increase the expression of Cyp6g1 in tissues important for detoxification, the midgut, Malpighian tubules, and the fat body. This study provides a significant example of how changes in tissue-specific gene expression caused by transposable-element insertions can contribute to adaptation.

Adaptation, Biological↗

PubMed2006

A comparison of Drosophila melanogaster detoxification gene induction responses for six insecticides, caffeine and phenobarbital.

Modifications of metabolic pathways are important in insecticide resistance evolution. Mutations leading to changes in expression levels or substrate specificities of cytochrome P450 (P450), glutathione-S-transferase (GST) and esterase genes have been linked to many cases of resistance with the responsible enzyme shown to utilize the insecticide as a substrate. Many studies show that the substrates of enzymes are capable of inducing the expression of those enzymes. We investigated if this was the case for insecticides and the enzymes responsible for their metabolism. The induction responses for P450s, GSTs and esterases to six different insecticides were investigated using a custom designed microarray in Drosophila melanogaster. Even though these gene families can all contribute to insecticide resistance, their induction responses when exposed to insecticides are minimal. The insecticides spinosad, diazinon, nitenpyram, lufenuron and dicyclanil did not induce any P450, GST or esterase gene expression after a short exposure to high lethal concentrations of insecticide. DDT elicited the low-level induction of one GST and one P450. These results are in contrast to induction responses we observed for the natural plant compound caffeine and the barbituate drug phenobarbital, both of which highly induced a number of P450 and GST genes under the same short exposure regime. Our results indicate that, under the insecticide exposure conditions we used, constitutive over-expression of metabolic genes play more of a role in insect survival than induction of members of these gene families.

Animals↗

PubMed2006

The insect growth regulator insecticide cyromazine causes earlier emergence in Drosophila melanogaster.

The insecticide cyromazine, classified as an insect growth regulator, inhibits the growth and development of Diptera. The precise mode of cyromazine action remains unknown. We investigated mortality and developmental time effects after exposing first instar Drosophila melanogaster larvae to cyromazine for 8-h intervals. Significant increases in mortality were only observed for cyromazine exposure within the first 16 h of the first instar stage, suggesting that cyromazine accumulates in the larvae over time and that there is a delay between cyromazine exposure and effect. We observed that exposure to cyromazine during the early first instar stage resulted in earlier eclosion of adults when compared to cyromazine exposure at later first instar stages. The presence of 20-hydroxyecdysone during cyromazine exposure significantly reduced the lethal effect of cyromazine. We raise the possibility that the mode of cyromazine action is related to the development hormone, 20-hydroxyecdysone.

Analysis of Variance↗

PubMed2005

Cyp12a4 confers lufenuron resistance in a natural population of Drosophila melanogaster.

Lufenuron is an insect growth regulator insecticide mainly used for the control of the cat flea. To understand mechanisms of resistance to lufenuron, we have characterized lufenuron resistance in a natural population of Drosophila melanogaster. In this study we have used precise genetic mapping to identify a mechanism of lufenuron resistance: the overexpression of the cytochrome P450 gene Cyp12a4. Cyp12a4 is predicted to encode a mitochondrial cytochrome P450 enzyme. Expression of Cyp12a4 in D. melanogaster third-instar larvae was detected in the midgut and Malpighian tubules of both lufenuron-resistant and wild-type strains. The level of Cyp12a4 expression in the midgut is higher in the lufenuron-resistant strain than in wild-type strains. Driving the expression of Cyp12a4 in the midgut and Malpighian tubules by using the GAL4/UAS gene expression system results in lufenuron resistance, but it does not result in resistance to three other insecticide classes. Transgenic expression of Cyp12a4 in a ubiquitous expression pattern results in late embryonic lethality, suggesting that high-level ectopic expression of Cyp12a4 is detrimental to development.

Animals↗

PubMed2004

The genetics and genomics of insecticide resistance.

The past ten years have seen the elucidation of the molecular basis of insect resistance to many chemical insecticides. Target genes, mostly in the nervous system, have been identified and cloned from Drosophila melanogaster and resistance-associated mutations have been examined in a range of pest insects. More recently, with the advent of annotated insect genomes, resistance mediated by complex multi-gene enzyme systems such as esterases, cytochrome p450s and glutathione-S-transferases has also been elucidated. In this article, we review the impact of Drosophila genetics on the field of insect resistance and focus on the current and future impact of genomics. These studies enable us to address three fundamental questions in the evolution of resistance. How many genes are involved? How many mutations are there within these genes? How often do these mutations arise in natural populations?

Acetylcholinesterase↗

PubMed2003

The insecticidal toxin makes caterpillars floppy 2 (Mcf2) shows similarity to HrmA, an avirulence protein from a plant pathogen.

The Photorhabdus luminescens W14 toxin encoding gene makes caterpillars floppy (mcf) was discovered due to its ability to kill caterpillars when expressed in Escherichia coli. Here we describe a homologue of mcf (renamed as mcf1), termed mcf2, discovered in the same genome. The mcf2 gene predicts another large toxin whose central domain, like Mcf1, also shows limited homology to Clostridium cytotoxin B. However, the N-terminus of Mcf2 shows significant similarity to the type-III secreted effector HrmA from the plant pathogen Pseudomonas syringae and no similarity to the N-terminus of Mcf1. HrmA is a plant avirulence gene whose transient expression in tobacco cells results in cell death. Here we show that E. coli expressing Mcf2 can, like E. coli expressing Mcf1, kill insects. Further, expression of the c-Myc tagged N-terminus of Mcf2, the region showing similarity to HrmA, results in nuclear localisation of the fusion protein and subsequent destruction of transfected mammalian cells. The Mcf1 and Mcf2 toxins therefore belong to a family of high molecular mass toxins, differing at their N-termini, which encode different effector domains.

Amino Acid Sequence↗

PubMed2002

Genomic islands in Photorhabdus.

Genomic islands are responsible for unique aspects of bacterial behavior such as symbiosis and pathogenicity. Photorhabdus luminescens is a pathogen of insects that spends part of its lifecycle in symbiosis with a nematode. Here, we describe novel genomic islands from Photorhabdus that are involved in symbiosis and pathogenicity, and discuss the inter-relationship between virulence factors used against invertebrates and vertebrates.

Amino Acid Sequence↗

PubMed2002

Bacterial infection of a model insect: Photorhabdus luminescens and Manduca sexta.

Invertebrates, including insects, are being developed as model systems for the study of bacterial virulence. However, we understand little of the interaction between bacteria and specific invertebrate tissues or the immune system. To establish an infection model for Photorhabdus, which is released directly into the insect blood system by its nematode symbiont, we document the number and location of recoverable bacteria found during infection of Manduca sexta. After injection into the insect larva, P. luminescens multiplies in both the midgut and haemolymph, only later colonizing the fat body and the remaining tissues of the cadaver. Bacteria persist by suppressing haemocyte-mediated phagocytosis and culture supernatants grown in vitro, as well as plasma from infected insects, suppress phagocytosis of P. luminescens. Using GFP-labelled bacteria, we show that colonization of the gut begins at the anterior of the midgut and proceeds posteriorly. Within the midgut, P. luminescens occupies a specific niche between the extracellular matrix and basal membrane (lamina) of the folded midgut epithelium. Here, the bacteria express the gut-active Toxin complex A (Tca) and an RTX-like metalloprotease PrtA. This close association of the bacteria with the gut, and the production of toxins and protease, triggers a massive programmed cell death of the midgut epithelium.

Animals↗