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Biomedical subjects

J Ferré

Publications and source records attributed to J Ferré.

At least 19 recordsLinked to original sources
PubMed2004

Domain wall creep in magnetic wires.

The dynamics of a 1D domain wall (DW) in magnetic wires patterned in 2D ultrathin Co films is studied as a function of the wire width w0. The DW velocity v(H) is hugely reduced when w0 is decreased, and its field dependence is consistent with a creep process with a critical exponent micro=1/4. The effective critical field scales as (1/w0). Measurements of v(H) in wires with controlled artificial defects show that this arises from the edge roughness introduced by patterning. We show that the creep law can be renormalized by introducing a topologically induced critical field proportional to (1/w0).

Journal Article↗
PubMed2004

Physical properties of aqueous suspensions of goethite (alpha-FeOOH) nanorods. Part I: In the isotropic phase.

Depending on volume fraction, aqueous suspensions of goethite (alpha-FeOOH) nanorods form a liquid-crystalline nematic phase (above 8.5%) or an isotropic liquid phase (below 5.5%). In this article, we investigate by small-angle X-ray scattering, magneto-optics, and magnetometry the influence of a magnetic field on the isotropic phase. After a brief description of the synthesis and characterisation of the goethite nanorod suspensions, we show that the disordered phase becomes very anisotropic under a magnetic field that aligns the particles. Moreover, we observe that the nanorods align parallel to a small field (< 350 mT), but realign perpendicular to a large enough field (> 350 mT). This phenomenon is interpreted as due to the competition between the influence of the nanorod permanent magnetic moment and a negative anisotropy of magnetic susceptibility. Our interpretation is supported by the behaviour of the suspensions in an alternating magnetic field. Finally, we propose a model that explains all experimental observations in a consistent way.

Journal Article↗
PubMed2002

Outstanding magnetic properties of nematic suspensions of goethite (alpha-FeOOH) nanorods.

Aqueous suspensions of goethite (alpha-FeOOH) nanorods form a mineral lyotropic nematic phase that aligns in a very low magnetic field (20 mT for samples 20 microm thick). The particles orient along the field direction at intensities smaller than 350 mT, but they reorient perpendicular to the field beyond 350 mT. This outstanding behavior is also observed in the isotropic phase which has a very strong magnetic-field induced birefringence that could be interesting for applications. We interpret these magnetic effects as resulting from a competition between a nanorod remanent magnetic moment and a negative anisotropy of its magnetic susceptibility.

Journal Article↗
PubMed2001

Update on the detection of beta-exotoxin in Bacillus thuringiensis strains by HPLC analysis.

AIMS: The current work aimed to study the presence of beta-exotoxin by high-performance liquid chromatography (HPLC) in supernatant fluids from final whole cultures of the 69 type strains and 13 subtypes of Bacillus thuringiensis strains, as well as from some insecticidal strains. METHODS AND RESULTS: Results from HPLC and bioassays with Ephestia kuhniella (Lepidoptera Pyralidae) were compared. Type I beta-exotoxin was only detected in type strains representing serotypes H1, H9 and H10a,10b. Discrepancies between HPLC and bioassays were found in H8a,8b and some insecticidal strains, which suggests the occurrence of another soluble toxin different from type I beta-exotoxin, possibly type II beta-exotoxin. CONCLUSION: This study shows the need to use bioassays to determine the presence of beta-exotoxin activity. However, HPLC is a fast and sensitive technique if only type I beta-exotoxin is to be determined. The occurrence of beta-exotoxin in a type strain does not imply production of this metabolite by other strains belonging to the same serovar. SIGNIFICANCE AND IMPACT OF THE STUDY: These results complete the characterization of type strains belonging to the International Entomopathogenic Bacillus Collection (Institut Pasteur, Paris, France).

Adenosine↗
PubMed2001

Variation in susceptibility to Bacillus thuringiensis toxins among unselected strains of Plutella xylostella.

So far, the only insect that has evolved resistance in the field to Bacillus thuringiensis toxins is the diamondback moth (Plutella xylostella). Documentation and analysis of resistant strains rely on comparisons with laboratory strains that have not been exposed to B. thuringiensis toxins. Previously published reports show considerable variation among laboratories in responses of unselected laboratory strains to B. thuringiensis toxins. Because different laboratories have used different unselected strains, such variation could be caused by differences in bioassay methods among laboratories, genetic differences among unselected strains, or both. Here we tested three unselected strains against five B. thuringiensis toxins (Cry1Aa, Cry1Ab, Cry1Ac, Cry1Ca, and Cry1Da) using two bioassay methods. Tests of the LAB-V strain from The Netherlands in different laboratories using different bioassay methods yielded only minor differences in results. In contrast, side-by-side comparisons revealed major genetic differences in susceptibility between strains. Compared with the LAB-V strain, the ROTH strain from England was 17- to 170-fold more susceptible to Cry1Aa and Cry1Ac, respectively, whereas the LAB-PS strain from Hawaii was 8-fold more susceptible to Cry1Ab and 13-fold more susceptible to Cry1Da and did not differ significantly from the LAB-V strain in response to Cry1Aa, Cry1Ac, or Cry1Ca. The relative potencies of toxins were similar among LAB-V, ROTH, and LAB-PS, with Cry1Ab and Cry1Ac being most toxic and Cry1Da being least toxic. Therefore, before choosing a standard reference strain upon which to base comparisons, it is highly advisable to perform an analysis of variation in susceptibility among field and laboratory populations.

Animals↗
PubMed2001

High genetic variability for resistance to Bacillus thuringiensis toxins in a single population of diamondback moth.

The long-term benefit of insecticidal products based on Cry toxins, either in sprays or as transgenic crops, is threatened by the development of resistance by target pests. The models used to predict evolution of resistance to Cry toxins most often are monogenic models in which two alleles are used. Moreover, the high-dose/refuge strategy recommended for implementation with transgenic crops relies on the assumption that the resistance allele is recessive. Using selection experiments, we demonstrated the occurrence in a laboratory colony of diamondback moth of two different genes (either allelic or nonallelic) that confer resistance to Cry1Ab. At the concentration tested, resistance was dominant in one selection line and partially recessive in the other. Resistant insects from the two selection lines also differed in their cross-resistance patterns. The diamondback moth colony was derived from a field population from the Philippines, which originally showed a different resistance phenotype. This is the first time that an insect population has been directly shown to carry more than one gene conferring resistance to the same Cry toxin.

Animals↗
PubMed2001

Shared binding sites in Lepidoptera for Bacillus thuringiensis Cry1Ja and Cry1A toxins.

Bacillus thuringiensis toxins act by binding to specific target sites in the insect midgut epithelial membrane. The best-known mechanism of resistance to B. thuringiensis toxins is reduced binding to target sites. Because alteration of a binding site shared by several toxins may cause resistance to all of them, knowledge of which toxins share binding sites is useful for predicting cross-resistance. Conversely, cross-resistance among toxins suggests that the toxins share a binding site. At least two strains of diamondback moth (Plutella xylostella) with resistance to Cry1A toxins and reduced binding of Cry1A toxins have strong cross-resistance to Cry1Ja. Thus, we hypothesized that Cry1Ja shares binding sites with Cry1A toxins. We tested this hypothesis in six moth and butterfly species, each from a different family: Cacyreus marshalli (Lycaenidae), Lobesia botrana (Tortricidae), Manduca sexta (Sphingidae), Pectinophora gossypiella (Gelechiidae), P. xylostella (Plutellidae), and Spodoptera exigua (Noctuidae). Although the extent of competition varied among species, experiments with biotinylated Cry1Ja and radiolabeled Cry1Ac showed that Cry1Ja and Cry1Ac competed for binding sites in all six species. A recent report also indicates shared binding sites for Cry1Ja and Cry1A toxins in Heliothis virescens (Noctuidae). Thus, shared binding sites for Cry1Ja and Cry1A occur in all lepidopteran species tested so far.

Amino Acid Sequence↗
PubMed2001

Mannose phosphate isomerase isoenzymes in Plutella xylostella support common genetic bases of resistance to Bacillus thuringiensis toxins in Llpidopteran species.

A strong correlation between two mannose phosphate isomerase (MPI) isoenzymes and resistance to Cry1A toxins from Bacillus thuringiensis has been found in a Plutella xylostella population. MPI linkage to Cry1A resistance had previously been reported for a Heliothis virescens population. The fact that the two populations share similar biochemical, genetic, and cross-resistance profiles of resistance suggests the occurrence of homologous resistance loci in both species.

Animals↗
PubMed2001

Different mechanisms of resistance to Bacillus thuringiensis toxins in the indianmeal moth.

Susceptibility to protoxin and toxin forms of Cry1Ab and the binding of (125)I-labeled Cry1Ab and Cry1Ac has been examined in three Plodia interpunctella colonies, one susceptible (688(s)) and two resistant (198(r) and Dpl(r)) to Bacillus thuringiensis. Toxicological studies showed that the 198(r) colony was 11-fold more resistant to Cry1Ab protoxin than to Cry1Ab activated toxin, whereas the Dpl(r) colony was 4-fold more resistant to protoxin versus toxin. Binding results with (125)I-labeled toxins indicated the occurrence of two different binding sites for Cry1Ab in the susceptible insects, one of them shared with Cry1Ac. Cry1Ab binding was found to be altered in insects from both resistant colonies, though in different ways. Compared with the susceptible colony, insects from the Dpl(r) colony showed a drastic reduction in binding affinity (60-fold higher K(d)), although they had similar concentrations of binding sites. Insects from the 198(r) colony showed a slight reduction in both binding affinity and binding site concentration (five-fold-higher K(d) and ca. three-fold-lower R(t) compared with the 688(s) colony). No major difference in Cry1Ac binding was found among the three colonies. The fact that the 198(r) colony also has a protease-mediated mechanism of resistance (B. Oppert, R. Hammel, J. E. Throne, and K. J. Kramer, J. Biol. Chem. 272:23473-23476, 1997) is in agreement with our toxicological data in which this colony has a different susceptibility to the protoxin and toxin forms of Cry1Ab. It is noteworthy that the three colonies used in this work derived originally from ca. 100 insects, which reflects the high variability and high frequency of B. thuringiensis resistance genes occurring in natural populations.

Animals↗
PubMed2000

Screening for Bacillus thuringiensis crystal proteins active against the cabbage looper, Trichoplusia ni.

Toxicity tests were performed to find among Cry1 and Cry2 Bacillus thuringiensis crystal proteins those with high activity against the cabbage looper. Tests were performed with neonate larvae on surface-contaminated artificial diet. The crystal proteins found to be toxic were, from higher to lower toxicity: Cry1Ac, Cry1Ab, Cry1C, Cry2Aa, Cry1J, and Cry1F (LC50 of 1.14.1, 3.4-4.4, 12, 34, 87, and 250 ng/cm2, respectively). Cry1B, Cry1D, and Cry1E can be considered nontoxic (LC50 higher than 2500 ng/cm2). Cry1Aa was moderately toxic to nontoxic, depending on the source (LC50 of 420 ng/cm2 from PGS and 8100 ng/cm2 from Ecogen). In vitro binding assays with trypsin-activated 125I-labeled Cry1Aa, Cry1Ab, and Cry1Ac crystal proteins and brush border membrane vesicles from midgut larvae showed a direct correlation between toxicity and binding affinity. Heterologous competition experiments indicated that Cry1Aa and Cry1F bind, though only at very high concentrations, to the Cry1Ab/Cry1Ac shared high-affinity binding site.

Animals↗
PubMed2000

Characterization of Bacillus thuringiensis ser. balearica (Serotype H48) and ser. navarrensis (serotype H50): two novel serovars isolated in Spain.

The novel strains of Bacillus thuringiensis PM9 and NA69, isolated from soil samples in Spain, were classified and characterized in terms of their crystal proteins, plasmid profile, cry genes content, and their toxicological properties against several species of Lepidoptera, Coleoptera, and Diptera. Both strains share morphological and biochemical characteristics with previously described B. thuringiensis strains, although their unique H antigens identify them as two new serotypes. Two new serovar names, B. thuringiensis serovar balearica (H serotype 48) and B. thuringiensis serovar navarrensis (H serotype 50) are proposed for the type strains PM9 and NA69, respectively.

Animals↗
PubMed2000

Genetic and biochemical approach for characterization of resistance to Bacillus thuringiensis toxin Cry1Ac in a field population of the diamondback moth, Plutella xylostella.

Four subpopulations of a Plutella xylostella (L.) strain from Malaysia (F(4) to F(8)) were selected with Bacillus thuringiensis subsp. kurstaki HD-1, Bacillus thuringiensis subsp. aizawai, Cry1Ab, and Cry1Ac, respectively, while a fifth subpopulation was left as unselected (UNSEL-MEL). Bioassays at F(9) found that selection with Cry1Ac, Cry1Ab, B. thuringiensis subsp. kurstaki, and B. thuringiensis subsp. aizawai gave resistance ratios of >95, 10, 7, and 3, respectively, compared with UNSEL-MEL (>10,500, 500, >100, and 26, respectively, compared with a susceptible population, ROTH). Resistance to Cry1Ac, Cry1Ab, B. thuringiensis subsp. kurstaki, and B. thuringiensis subsp. aizawai in UNSEL-MEL declined significantly by F(9). The Cry1Ac-selected population showed very little cross-resistance to Cry1Ab, B. thuringiensis subsp. kurstaki, and B. thuringiensis subsp. aizawai (5-, 1-, and 4-fold compared with UNSEL-MEL), whereas the Cry1Ab-, B. thuringiensis subsp. kurstaki-, and B. thuringiensis subsp. aizawai-selected populations showed high cross-resistance to Cry1Ac (60-, 100-, and 70-fold). The Cry1Ac-selected population was reselected (F(9) to F(13)) to give a resistance ratio of >2,400 compared with UNSEL-MEL. Binding studies with (125)I-labeled Cry1Ab and Cry1Ac revealed complete lack of binding to brush border membrane vesicles prepared from Cry1Ac-selected larvae (F(15)). Binding was also reduced, although less drastically, in the revertant population, which indicates that a modification in the common binding site of these two toxins was involved in the resistance mechanism in the original population. Reciprocal genetic crosses between Cry1Ac-reselected and ROTH insects indicated that resistance was autosomal and showed incomplete dominance. At the highest dose of Cry1Ac tested, resistance was recessive while at the lowest dose it was almost completely dominant. The F(2) progeny from a backcross of F(1) progeny with ROTH was tested with a concentration of Cry1Ac which would kill 100% of ROTH moths. Eight of the 12 families tested had 60 to 90% mortality, which indicated that more than one allele on separate loci was responsible for resistance to Cry1Ac.

Animals↗
PubMed2000

Development and characterization of diamondback moth resistance to transgenic broccoli expressing high levels of Cry1C.

A field-collected colony of the diamondback moth, Plutella xylostella, had 31-fold resistance to Cry1C protoxin of Bacillus thuringiensis. After 24 generations of selection with Cry1C protoxin and transgenic broccoli expressing a Cry1C protein, the resistance that developed was high enough that neonates of the resistant strain could complete their entire life cycle on transgenic broccoli expressing high levels of Cry1C. After 26 generations of selection, the resistance ratios of this strain to Cry1C protoxin were 12,400- and 63,100-fold, respectively, for the neonates and second instars by a leaf dip assay. The resistance remained stable until generation 38 (G38) under continuous selection but decreased to 235-fold at G38 when selection ceased at G28. The Cry1C resistance in this strain was seen to be inherited as an autosomal and incompletely recessive factor or factors when evaluated using a leaf dip assay and recessive when evaluated using Cry1C transgenic broccoli. Saturable binding of (125)I-Cry1C was found with brush border membrane vesicles (BBMV) from both susceptible and Cry1C-resistant strains. Significant differences in Cry1C binding to BBMV from the two strains were detected. BBMV from the resistant strain had about sevenfold-lower affinity for Cry1C and threefold-higher binding site concentration than BBMV from the susceptible strain. The overall Cry1C binding affinity was just 2.5-fold higher for BBMV from the susceptible strain than it was for BBMV from the resistant strain. These results suggest that reduced binding is not the major mechanism of resistance to Cry1C.

Animals↗
PubMed2000

Binding and toxicity of Bacillus thuringiensis protein Cry1C to susceptible and resistant diamondback moth (Lepidoptera: Plutellidae).

We studied mechanisms of resistance to Bacillus thuringiensis insecticidal crystal protein Cry1C in the diamondback moth, Plutella xylostella (L.). Binding assays with midgut brush border membrane vesicles prepared from whole larvae showed no significant difference between resistant and susceptible strains in binding of radioactively-labeled Cry1C. These results indicate that reduced binding of Cry1C to midgut membrane target sites did not cause resistance to Cry1C. Thus, the mechanism of resistance to Cry1C differs from that observed in several previously reported cases of resistance to Cry1A toxins in diamondback moth. We tested Cry1C toxin and Cry1C crystalline protoxin against resistant and susceptible larvae using leaf disk bioassays. After adjusting for the size difference between Cry1C toxin and protoxin, we found that with resistant larvae, toxin was significantly more toxic than protoxin. In contrast, with susceptible larvae, no significant difference in toxicity occurred between Cry1C toxin and protoxin. The resistance ratios for Cry1C were 19 for toxin and 48 for protoxin. These results suggest that reduced conversion of Cry1C protoxin to toxin is a minor mechanism of resistance to Cry1C. Because neither reduced binding nor reduced conversion of protoxin to toxin appear to be major mechanisms, one or more other mechanisms are important in diamondback moth resistance to Cry1C.

Animals↗
PubMed1999

Factors involved in GLUT-1 glucose transporter gene transcription in cardiac muscle.

Glucose constitutes a major fuel for the heart, and high glucose uptake during fetal development is coincident with the highest level of expression of the glucose transporter GLUT-1 during life. We have previously reported that GLUT-1 is repressed perinatally in rat heart, and GLUT-4, which shows a low level of expression in the fetal stage, becomes the main glucose transporter in the adult. Here, we show that the perinatal expression of GLUT-1 and GLUT-4 glucose transporters in heart is controlled directly at the level of gene transcription. Transient transfection assays show that the -99/-33 fragment of the GLUT-1 gene is sufficient to drive transcriptional activity in rat neonatal cardiomyocytes. Electrophoretic mobility shift assays demonstrate that the transcription factor Sp1, a trans-activator of GLUT-1 promoter, binds to the -102/-82 region of GLUT-1 promoter during the fetal state but not during adulthood. Mutation of the Sp1 site in this region demonstrates that Sp1 is essential for maintaining a high transcriptional activity in cardiac myocytes. Sp1 is markedly down-regulated both in heart and in skeletal muscle during neonatal life, suggesting an active role for Sp1 in the regulation of GLUT-1 transcription. In all, these results indicate that the expression of GLUT-1 and GLUT-4 in heart during perinatal development is largely controlled at a transcriptional level by mechanisms that might be related to hyperplasia and that are independent from the signals that trigger cell hypertrophy in the developing heart. Furthermore, our results provide the first functional insight into the mechanisms regulating muscle GLUT-1 gene expression in a live animal.

Age Factors↗
PubMed1999

Optimization of solid-phase microextraction conditions using a response surface methodology to determine organochlorine pesticides in water by gas chromatography and electron-capture detection.

A response surface methodology was applied to optimise the solid-phase microextraction (SPME) conditions using a polyacrylate-coated fiber to determine thirteen organochlorine pesticides from water. Analyses were performed using gas chromatography-electron-capture detection. Variables affecting absorption in both the headspace and immersion extraction were optimised by using a response surface generated with a Doehlert design, and the results were compared. The immersion SPME method was selected since higher recoveries were obtained for most of the compounds studied. The method developed was applied to the analysis of tap and Ebro river water samples. The linear range of most pesticides for real samples was found to be between 0.001 and 2.5 micrograms l-1 and the limits of detection were between 0.15 and 0.35 ng l-1. The repeatability and the reproducibility between days of the method (n = 6), expressed as relative standard deviation, for tap water spiked at a level of 1 ng l-1 were between 5.7 and 25.6% and between 7.6 and 26.5%, respectively.

Chromatography, Gas↗
PubMed1999

Insecticidal activity of strains of Bacillus thuringiensis on larvae and adults of Bactrocera oleae Gmelin (Dipt. Tephritidae).

The olive fly, Bactrocera oleae, is the key pest on olives in the Mediterranean area. The pest can destroy, in some cases, up to 70% of the olive production. Its control relies mainly on chemical treatments, sometimes applied by aircraft over vast areas, with their subsequent ecological and toxicological side effects. Bacillus thuringiensis is a spore-forming soil bacterium which produces a protein crystal toxic to some insects, including the orders of Lepidoptera, Diptera, and Coleoptera and other invertebrates. The aim of this study was to search for isolates toxic to B. oleae. Several hundred B. thuringiensis isolates were obtained from olive groves and olive presses in different areas of Greece, Sardinia (Italy), and Spain and from cooperating scientists throughout the world. Some isolates were found toxic only to adults or larvae and some to both stages of the olive fly. In addition, the most toxic isolates were assayed on Opius concolor Szepl. (Hym. Braconidae), the most important parasitoid of the olive fruit fly. Only 3 isolates out of 14 gave significant mortality against this parasitoid. Several of the most toxic crystalliferous isolates may contain novel toxins since they gave no PCR products when probed with primers specified for 39 known toxin genes.

Animals↗