Search results for "Midgut"
showing 10 items of 81 documents
Midgut pseudotumors and the maintenance of tissue homeostasis: studies on aging and manipulated stick insects.
2009
Stick insects (Carausius morosus) develop pseudotumors in aging adults. Pseudotumor formation starts at the M2 midgut region where an accumulation of stomatogastric nerve terminals is observed. Pseudotumors arise from dying columnar cells whose basal parts form an “amorphous substance” at the basement membrane whereas the apical parts, including the nucleus, are expelled into the gut lumen. The “amorphous substance” is ensheathed by hemocytes. These nodules, which do not melanize, characterize the phenotype of the pseudotumors. With age, cell death and pseudotumor infestation increases. It is shown that the maintenance of midgut tissue homoeostasis is disturbed and becomes more serious with…
Bacillus thuringiensis Cry1Ac Toxin-Binding and Pore-Forming Activity in Brush Border Membrane Vesicles Prepared from Anterior and Posterior Midgut R…
2008
ABSTRACT It is generally accepted that Bacillus thuringiensis Cry toxins insert into the apical membrane of the larval midgut after binding to specific receptors, and there is evidence that the distribution of binding molecules along the midgut is not uniform. By use of the voltage-sensitive dye DiSC 3 (5) and 125 I-labeled Cry1Ac, we have measured the effect of Cry1Ac in terms of permeabilization capacity and of binding parameters on brush border membrane vesicles (BBMV) prepared from the anterior and the posterior regions of the larval midgut from two insect species, Manduca sexta and Helicoverpa armigera . The permeabilizing activity was significantly higher with BBMV from the posterior …
Midgut microbiota and host immunocompetence underlie Bacillus thuringiensis killing mechanism
2016
Bacillus thuringiensis is a widely used bacterial entomopathogen producing insecticidal toxins, some of which are expressed in insect-resistant transgenic crops. Surprisingly, the killing mechanism of B. thuringiensis remains controversial. In particular, the importance of the septicemia induced by the host midgut microbiota is still debated as a result of the lack of experimental evidence obtained without drastic manipulation of the midgut and its content. Here this key issue is addressed by RNAi-mediated silencing of an immune gene in a lepidopteran host Spodoptera littoralis, leaving the midgut microbiota unaltered. The resulting cellular immunosuppression was characterized by a reduced …
Mode of action of Bacillus thuringiensis PS86Q3 strain in hymenopteran forest pests
2001
The mode of action of Cry toxins has been described principally in lepidopteran insects as a multistep process. In this work we describe the mode of action of a Cry toxin active in the common pine sawfly Diprion pini (Hymenoptera, Diprionidae), considered a major forest pest in Europe. Strain PS86Q3 contains a long bipyramidal crystal composed of five major proteins. The N-terminal sequence shows that the 155 kDa protein corresponds to Cry5B toxin and the other proteins belong to the Cry5A subgroup. PCR analysis indicates the presence of cry5Ac and cry5Ba genes, suggesting that Cry5A protein should be Cry5Ac. Activation of protoxins with trypsin or with midgut content from D. pini and Cepha…
Cadmium binding proteins induced in exposed freshwater crayfish Procambarus clarkii.
1989
This work describes results on the characterization of cadmium binding proteins (Cd-BPs) obtained from cadmium exposed freshwater crayfish Procambarus clarkii. After acclimation to laboratory conditions, induction of Cd-BPs was achieved by water exposure at a concentration of 100 micrograms Cd/L during 2, 15, and 30 d. In accordance with the method followed by Engel and Brouwer, in each case two midgut glands were minced and homogenized in Tris-HC1 buffer with PMSF to prevent protease activity and DTT to maintain reducing conditions. The homogenate was centrifuged, heat treated, applied to a column of Sephadex G-75, and eluted with the same buffer (pH 8.6). Absorbances of the fractions coll…
Midgut aminopeptidase N isoforms from Ostrinia nubilalis: Activity characterization and differential binding to Cry1Ab and Cry1Fa proteins from Bacil…
2013
Aminopeptidase N (APN) isoforms from Lepidoptera are known for their involvement in the mode of action of insecticidal Cry proteins from Bacillus thuringiensis. These enzymes belong to a protein family with at least eight different members that are expressed simultaneously in the midgut of lepidopteran larvae. Here, we focus on the characterization of the APNs from Ostrinia nubilalis (OnAPNs) to identify potential Cry receptors. We expressed OnAPNs in insect cells using a baculovirus system and analyzed their enzymatic activity by probing substrate specificity and inhibitor susceptibility. The interaction with Cry1Ab and Cry1Fa proteins (both found in transgenic insect-resistant maize) was …
Reduced levels of membrane-bound alkaline phosphatase in Vip3Aa-resistant Heliothis virescens
2020
ABSTRACTThe Vip3Aa insecticidal protein fromBacillus thuringiensis(Bt) is produced by specific transgenic corn and cotton varieties for efficient control of target lepidopteran pests. The main threat to this technology is the evolution of resistance in targeted insect pests, thus understanding the mechanistic basis of resistance is crucial to deploy the most appropriate strategies for resistance management. In this work, a laboratory-selected colony ofHeliothis virescens(Vip-Sel) highly resistant to the Vip3Aa protein was used to test whether an alteration of membrane receptors in the insect midgut might explain the resistance phenotype. Binding of125I-labeled Vip3Aa to brush border membran…
Histological and electron microscopical observations on the effects of lead on gills and midgut gland ofProcambarus clarkii
1991
Adult intermolt specimen of Procambarus clarkii (Crustacea, Decapoda) have been treated for 96 hours in aquaria with 100mg/l of lead. The gills and midgut gland were processed and studied in the electron microscope. The gill filament shows important changes in the ultrastructure of the epithelial cells and the cuticle. The hepatopancreatic cells studied (i.e. the vacuolated and dark cells) do not show noticeable structural changes but accumulate lead (electrondense precipitates) mainly in lysosomes.
Reduced membrane-bound alkaline phosphatase does not affect binding of Vip3Aa in a Heliothis virescens resistant colony
2020
The Vip3Aa insecticidal protein from Bacillus thuringiensis (Bt) is produced by specific transgenic corn and cotton varieties for efficient control of target lepidopteran pests. The main threat to this technology is the evolution of resistance in targeted insect pests and understanding the mechanistic basis of resistance is crucial to deploy the most appropriate strategies for resistance management. In this work, we tested whether alteration of membrane receptors in the insect midgut might explain the >
Differences in the midgut proteolytic activity of twoHeliothis virescens strains, one susceptible and one resistant toBacillus thuringiensis toxins
1996
The development of resistance to Bacillus thuringiensis toxic proteins is a growing concern because it could threaten both conventional and gene transfer use of this environmentally safe biological insecticide. The most common mechanism of resistance involves changes in binding affinity of toxin receptors in the insect midgut membrane. This has not been the case in Heliothis virescens. We have investigated changes in midgut proteolytic activity as a possibility to explain the resistance observed in this insect species. We have developed an improvement of known methods to demonstrate proteolytic activity in crude extracts. Using this method we have found differences in the proteolytic activi…