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M Raymond

Publications and source records attributed to M Raymond.

At least 55 records · Page 3Linked to original sources
PubMed1996

Testing the unique amplification event and the worldwide migration hypothesis of insecticide resistance genes with sequence data.

In the mosquito Culex pipiens, over-production of esterases is a common insecticide resistance mechanism. Different alleles at the esterase A and B loci are known to occur in natural populations, as shown by enzyme electrophoresis and RFLP studies on the esterase B locus. Here we analyse the variability of the esterase A locus at the nucleotide level in mosquitoes possessing or lacking over-produced esterase A. A surprisingly high level of nucleotide polymorphism is found in coding and noncoding regions, and the extent of polymorphism detected is higher than that previously described for the most polymorphic loci in Drosophila. We also show that eight strains from different localities (Africa, America, Asia) that possess the over-produced esterase A2 share the same nucleotide sequence at the esterase A locus, strongly supporting the evolutionary scenario of a unique event of amplification of this gene followed by dispersal through migration rather than the occurrence of multiple independent mutational events of the gene.

Amino Acid Sequence↗
PubMed1996

Existence of two acetylcholinesterases in the mosquito Culex pipiens (Diptera:Culicidae).

Two acetylcholinesterases (AChEs), AChE1 and AChE2, differing in substrate specificity and in some aspects of inhibitor sensitivity, have been characterized in the mosquito Culex pipiens. The results of ultracentrifugation in sucrose gradients and nondenaturing gel electrophoresis of AChE activity peak fractions show that each AChE is present as two molecular forms: one amphiphilic dimer possessing a glycolipid anchor and one hydrophilic dimer that does not interact with nondenaturing detergents. Treatment by phosphatidylinositol-specific phospholipase C converts each type of amphiphilic dimer into the corresponding hydrophilic dimer. Molecular forms of AChE1 have a lower electrophoretic mobility than those of AChE2. However, amphiphilic dimers and hydrophilic dimers have similar sedimentation coefficients (5.5S and 6.5S, respectively). AChE1 and AChE2 dimers, amphiphilic or hydrophilic, resist dithiothreitol reduction under conditions that allow reduction of Drosophila AChE dimers. In the insecticide-susceptible strain S-LAB, AChE1 is inhibited by 5 x 10(-4) M propoxur (a carbamate insecticide), whereas AChE2 is resistant. All animals are killed by this concentration of propoxur, indicating that only AChE1 fulfills the physiological function of neurotransmitter hydrolysis at synapses. In the insecticide-resistant strain, MSE, there is no mortality after exposure to 5 x 10(-4) M propoxur: AChE2 sensitivity to propoxur is unchanged, whereas AChE1 is now resistant to 5 x 10(-4) M propoxur. The possibility that AChE1 and AChE2 are products of tissue-specific posttranslational modifications of a single gene is discussed, but we suggest, based on recent results obtained at the molecular level in mosquitoes, that they are encoded by two different genes.

Acetylcholinesterase↗
PubMed1996

Dominance of insecticide resistance presents a plastic response.

Dominance level of insecticide resistance provided by one major gene (an insensitive acetylcholinesterase) in the mosquito Culex pipiens was studied in two distinct environments. Dominance level was found to be very different environments, varying from almost complete dominance to almost recessive when either propoxur (a carbamate insecticide) or chlorpyrifos (an organophosphorus insecticide) was used. To better understand this plastic response, three environmental parameters were manipulated and their interactions studied. For chlorpyrifos, each parameter had a small effect, but when all parameters were changed, the dominance level was greatly affected. For propoxur, one environmental parameter had a large effect by itself. It was further studied to understand the causal relationship of this plasticity. Recessivity of resistance was associated with more demanding environments. These results are discussed in the context of the various theories of the evolution of dominance. It appears that dominance of insecticide resistance cannot be directly predicted by Wright's physiological theory.

Animals↗
PubMed1996

Testing differentiation in diploid populations.

We examine the power of different exact tests of differentiation for diploid populations. Since there is not necessarily random mating within populations, the appropriate hypothesis to construct exact tests is that of independent sampling of genotypes. There are two categories of tests, FST-estimator tests and goodness of fit tests. In this latter category, we distinguish "allelic statistics", which account for the nature of alleles within genotypes, from "genotypic statistics" that do not. We show that the power of FST-estimator tests and of allelic goodness of fit tests are similar when sampling is balanced, and higher than the power of genotypic goodness of fit tests. When sampling is unbalanced, the most powerful tests are shown to belong to the allelic goodness of fit group.

Alleles↗
PubMed1996

An insensitive acetylcholinesterase in Culex pipiens (Diptera:Culicidae) from Portugal.

Resistance mechanisms of a strain (PRAIAS) of northern house mosquito, Culex pipiens L., collected in Portugal in 1993, and highly resistant to organophosphates and carbamates, were investigated by comparing the resistance characteristics to 3 organophosphorous (temephos, chlorpyrifos, malathion) and 1 carbamate (propoxur) insecticides in the presence or absence of synergists; and by determining the possible occurrence of overproduced esterases or insensitive acetylcholinesterase (AChE). The reference strain MSE from southern France, with an insensitive AChE, was included in all analyses for comparison. For organophosphorous insecticides, resistance in PRAIAS was caused by an insensitive AChE and an increase in oxidative metabolism, although the 2nd mechanism has only a marginal effect. For propoxur, the insensitive AChE was the only resistance mechanism detected. Biochemical properties of both the French and Portuguese insensitive AChEs were similar. We cannot exclude the possibility that PRAIAS and MSE strains possess exactly the same insensitive AChE allele.

Acetylcholinesterase↗
PubMed1996

Coamplification of esterase A and B genes as a single unit in Culex pipiens mosquitoes.

In Culex pipiens mosquitoes, resistance to organophosphorous insecticides often results from increased detoxification by two types of esterases, A and B, which are closely linked. Overproduction of all esterase B so far investigated (B1, B2, B4, B5 and B6) is from gene amplification. An esterase A gene (esterase A2) has recently been cloned from mosquitoes with the overproduced esterases A2 and B2, and amplification of this gene has also been reported. We describe the cDNA sequences of three additional esterase genes from insecticide-resistant strains of Culex pipiens originating from France and California which show at least 93 per cent homology with the esterase A2 gene sequence. Restriction enzyme mapping shows that the esterase A gene lies within 2.2 kb of the esterase B gene. In mosquitoes with overproduced esterases A2 and B2, the amplification level of esterase A is equal to that of esterase B suggesting that the genes are coamplified. Furthermore, we show that in one strain with an overproduced A esterase (A1), gene amplification cannot account for the increased protein level. This indicates that overproduction of esterases A can be achieved through two different mechanisms: gene amplification and a regulatory mechanism--the nature of which remains to be identified.

Animals↗
PubMed1996

[Resistance of insects to insecticides. Molecular mechanisms and epidemiology].

The aim of this paper is to indicate the main strengths which are involved in the spread of insecticide resistance genes. These forces are more or less well known in population genetics, there are: mutations which are involved in the creation of new alleles well adapted to insecticides; migration which is responsible for the geographical extension of resistance and selection which screened among the various alleles those which are best adapted in the geographical and ecological context. The biological model described in this paper is the mosquito Culex pipiens which is the best known model at that time. Many works have been done on the resistance to insecticides in this species. On the other hand, the molecular mechanisms involved in insecticide resistance have been described from various invertebrates.

Animals↗
PubMed1995

Commensalism, adaptation and gene flow: mosquitoes of the Culex pipiens complex in different habitats.

Two ecotypes have been described for Culex pipiens mosquitoes of the temperate zone: a human commensal type and a feral type, but their degree of evolutionary differentiation and taxonomic status are still unclear. The commensal form is characterized by life-history traits probably adaptive to underground man-made environments. This situation has sometimes been considered as an example of recent speciation although the existence of intermediate forms indicates that the balance between gene flow and disruptive selection should first be assessed. The present study was concerned with (1) the determination of biological traits involved in adaptation to commensalism, and (2) the pattern of gene flow within and between ecotypes in a restricted area. It was found that (1) significant differences in biological traits exist between mosquitoes from different habitats, (2) characteristics of the commensal type are not universal in mosquitoes from underground man-made habitats, (3) allozyme markers do not clearly differentiate ecotypes and (4) insecticide resistance genes, which reveal recent migration, occur in each ecotype. These results are discussed in the context of possible speciation due to commensalism.

Adaptation, Physiological↗
PubMed1995

Variation in the vector competence of Aedes polynesiensis for Wuchereria bancrofti.

The vector competences of 6 geographic strains of Aedes polynesiensis for Wuchereria bancrofti were studied using two types of experimental infections. Experimental infection of laboratory-bred mosquitoes fed on the carriers' forearms with different levels of microfilaraemia showed that microfilariae (mf) uptake was directly proportional to the carrier's mf density and, as mf densities decreased, concentration capacity of Ae. polynesiensis increased. It was also shown that infection has an important effect on mosquito mortality, and that the mortality rate differed among mosquito strains. In infections using artificial feeders, the mf uptake was closely regulated, thus showing differences in the vectorial efficiency of Ae. polynesiensis related to the geographic origin of the mosquito strain. The mosquitoes from the Society archipelago were more efficient intermediate hosts than geographically distant strains when infected with W. bancrofti from an island within the archipelago (Tahiti). Mosquito strains from the Society archipelago developed the highest proportion of infective-stage larvae and exhibited the lowest mortality rate when infected with sympatric Tahitian W. bancrofti.

Adult↗
PubMed1995

The same esterase B1 haplotype is amplified in insecticide-resistant mosquitoes of the Culex pipiens complex from the Americas and China.

In Culex pipiens, overproduction of nonspecific esterases is a common mechanism of resistance to organophosphate insecticides. The esterases are attributed to closely linked loci named A and B, and overproduction of all esterases B is due to gene amplification. In order to determine if the esterase B1 identified by electrophoretic studies in Culex pipiens mosquitoes from different countries is overproduced due to the amplification of the same DNA haplotype, the amplified region encompassing the structural esterase B1 gene was characterized by restriction mapping and RFLP. The same amplified haplotype was found in mosquitoes with an esterase B1 protein, independently of their geographical origin: French Guiana, Venezuela, Puerto Rico, California and China. Large variations in amplification levels were observed. It is concluded that B1 amplification has a unique origin, either in America or in Asia, and has subsequently spread by migration. This migration is more limited than that of A2-B2 esterases, since B1 is confined to the Americas, the Caribbean and part of China, whereas the A2-B2 distribution now includes the Americas, the Caribbean, Asia, Africa, the Pacific Islands and Europe.

Americas↗
PubMed1995

Testing heterozygote excess and deficiency.

Currently used tests of Hardy-Weinberg proportions do not take into account the nature of the alternative hypothesis, which is generally a heterozygote deficiency. Different exact tests, appropriate for small sample size and large number of alleles, are proposed in this perspective, and their properties are evaluated by power comparisons. Some tests are found to be close to optimal for the detection of inbreeding or heterozygote excess, one of which is a score test closely related to Robertson and Hill's estimator of the inbreeding coefficient. This test is also easily applied to multiple samples. Such tests are not always the most appropriate if alternative hypotheses differ from those considered here.

Alleles↗
PubMed1995

Resistance to organophosphorous insecticides in Culex pipiens quinquefasciatus (Diptera: Culicidae) from Martinique.

Before beginning a widespread control program against Culex pipiens quinquefasciatus in Martinique, resistance to temephos, chlorpyrifos, and two organophosphorous insecticides, was investigated at seven breeding sites. At LC95, populations exhibited resistance ratios between 6.9 and 11.6 for temephos and between 6.4 and 51.4 for chlorpyrifos. Overproduced esterases A2-B2 and B1, known to be involved in organophosphorous-resistance, were present at all breeding sites; esterases A2-B2 frequency was > 50% at all sites but one; and esterase B1 frequency was < 7%. Experimental treatment of three breeding sites with temephos induced no significant increase in resistance, but our esterase studies indicated a significant increase in the frequencies of esterase B1 and of a new highly active esterase C2. These results indicate that a large-scale C. p. quinquefasciatus control program with organophosphorous insecticides will induce a rapid increase of these resistance genes throughout Martinique. However, this may not necessarily result in high levels of resistance, because, at present, the level of gene amplification of esterase B still appears to be low.

Acetylcholinesterase↗
PubMed1994

Monitoring of monoclonal gammopathies: rational use of densitometry and rate nephelometry.

The follow-up of patients with monoclonal gammopathies at our institution includes serial serum protein electrophoresis (SPE) with densitometry and IgG, IgA, and IgM quantitative immunoglobulin (QIG) determinations by rate nephelometry. This retrospective audit compares monoclonal protein concentration as estimated by SPE versus QIG in 456 serial serum specimens from 105 patients to determine whether any of the tests provide redundant information. A comparison of the methods demonstrated good correlation between SPE (x-axis) and QIG (y-axis) quantitation for each immunoglobulin class: IgG had a slope of 1.45 and an intercept of 1.60 (Sy/x = 7.46, r = 0.96, n = 250); IgA had a slope of 1.30 and an intercept of -1.37 (Sy/x = 6.85, r = 0.96, n = 78); and IgM had a slope of 1.95 and an intercept of 2.06 (Sy/x = 5.16, r = 0.98, n = 128). The data for individual patients showed similar good correlations. Exceptions included IgA peaks "buried" in the beta region of the SPE (resulting in invalid SPE estimates of monoclonal protein concentration), and IgG peaks of less than 10 g/L (when background polyclonal IgG immunoglobulin skews the QIG estimate of monoclonal protein concentration). An algorithm is proposed whereby monoclonal protein concentration is measured by the specific QIG (i.e., IgG, IgA, or IgM) determination for the routine monitoring of patients, except for those with IgG peaks of less than 10 g/L that are followed by SPE.

Blood Protein Electrophoresis↗
PubMed1994

Resistance monitoring in Culex pipiens (Diptera: Culicidae) from central-eastern France.

Insensitive acetylcholinesterase (AceR) and five over-produced esterases (A1, A2 and B2, and A4 and B4) involved in detoxification are responsible for resistance to organophosphorous insecticides (OPs) in Culex pipiens L. from the Rhône-Alpes region, where C. pipiens control is mainly accomplished with the OPs temephos and chlorpyrifos using 0.15 mg/liter doses. The strong linkage disequilibria observed between esterases A1 and Est-20(0.64), esterases A4 and B4, and esterases A2 and B2 indicate that these genes were introduced in the Rhône-Alpes region. AceR and esterase A1, which appeared in the south of France 3 yr before the start of mosquito control in Rhône-Alpes, had the highest frequencies. All resistant genotypes were shown to be killed by 0.15 mg/liter temephos in natural breeding sites, but not by 0.15 mg/liter chlorpyrifos. These results are discussed in relation with mosquito control strategies.

Acetylcholinesterase↗
PubMed1994

Insecticide resistance genes in Culex pipiens (Diptera: Culicidae) from Italy: esterase B locus at the DNA level.

Restriction fragment length polymorphism (RFLP) analysis at the esterase B locus was performed in samples from four populations of Italian Culex pipiens pipiens L. to identify correctly, at the molecular level, the resistance gene. The absence of the amplified B2 haplotype was confirmed, indicating that it has not increased in frequency after its detection in continental Italy around 1985. The B4 haplotype was detected in all populations at the same frequencies as a previous starch gel survey. The possibility that B4 amplification has occurred only once and has migrated across western Mediterranean region is supported by the data. A1 also was detected indirectly by the presence of its closely linked B allele. The B5 haplotype apparently was absent. No amplification at the esterase B locus was detected, except B4, indicating a low rate of occurrence of new amplification at this locus.

Animals↗
PubMed1994

Insecticide susceptibility in mosquitoes (Diptera: Culicidae) from French Polynesia.

Susceptibility to six organophosphate (OP), two pyrethroid (PY), and one carbamate (C) insecticides was investigated in Culex pipiens quinquefasciatus Say, Aedes aegypti (L.), and Aedes polynesiensis Marks larvae from the island of Tahiti. Cx. p. quinquefasciatus and Ae. aegypti were compared with susceptible reference strains treated simultaneously. A low, but significant, resistance to bromophos (4.6x), chlorpyrifos (5.7x), fenthion (2.4x), fenitrothion (5.0x), temephos (4.3x) and permethrin (2.1x) was found in Cx. p. quinquefasciatus, and to malathion (1.5x), temephos (2.3x), permethrin (1.8x) and propoxur (1.7x) in Ae. aegypti. Cx. p. quinquefasciatus was shown to possess over-produced esterases A2 and B2, which are known to be involved in resistance to OPs in other countries. Ae. polynesiensis was less resistant than the Ae. aegypti reference strain to all insecticides except temephos (1.8x) and permethrin (6.7x). To determine whether Ae. polynesiensis had developed resistance to these insecticides in Tahiti, a geographical survey covering 12 islands of the Society, Tuamotu, Tubuai, Marquesas, and Gambier archipelagoes was undertaken with three insecticides (temephos, deltamethrin, and permethrin). Two- to threefold variations in LC50S were observed among collections. Results are discussed in relationship to the level of insecticide exposure on the different islands.

Animals↗
PubMed1994

Functional expression of P-glycoprotein in Saccharomyces cerevisiae confers cellular resistance to the immunosuppressive and antifungal agent FK520.

We have recently reported that expression in yeast cells of P-glycoprotein (P-gp) encoded by the mouse multidrug resistance mdr3 gene (Mdr3) can complement a null ste6 mutation (M. Raymond, P. Gros, M. Whiteway, and D. Y. Thomas, Science 256:232-234, 1992). Here we show that Mdr3 behaves as a fully functional drug transporter in this heterologous expression system. Photolabelling experiments indicate that Mdr3 synthesized in yeast cells binds the drug analog [125I]iodoaryl azidoprazosin, this binding being competed for by vinblastine and tetraphenylphosphonium bromide, two known multidrug resistance drugs. Spheroplasts expressing wild-type Mdr3 (Ser-939) exhibit an ATP-dependent and verapamil-sensitive decreased accumulation of [3H]vinblastine as compared with spheroplasts expressing a mutant form of Mdr3 with impaired transport activity (Phe-939). Expression of Mdr3 in yeast cells can confer resistance to growth inhibition by the antifungal and immunosuppressive agent FK520, suggesting that this compound is a substrate for P-gp in yeast cells. Replacement of Ser-939 in Mdr3 by a series of amino acid substitutions is shown to modulate both the level of cellular resistance to FK520 and the mating efficiency of yeast mdr3 transformants. The effects of these mutations on the function of Mdr3 in yeast cells are similar to those observed in mammalian cells with respect to drug resistance and transport, indicating that transport of a-factor and FK520 in yeast cells is mechanistically similar to drug transport in mammalian cells. The ability of P-gp to confer cellular resistance to FK520 in yeast cells establishes a dominant phenotype that can be assayed for the positive selection of intragenic revertants of P-gp inactive mutants, an important tool for the structure-function analysis of mammalian P-gp in yeast cells.

ATP Binding Cassette Transporter, Subfamily B, Mem↗