A Bacillus thuringiensis δ-endotoxin induces programmed cell death in mosquito larvae

Abstract

We present evidence that a d-endotoxin isolated from Bacillus thuringiensis subsp.israelensis induces programmed cell death in polytene midgut cells of Culex pipiens larvae. After exposure to toxin, polytene nuclei in the anterior region of the larval midgut undergo many of the morphological and physiological changes which are characteristic of apoptosis, including the ability to stain with the vital dye, acridine orange, and fragmentation of nuclear DNA as demonstrated by agarose gel electrophoresis and in situ TUNEL labeling. The temporal sequence of toxin ingestion, acridine orange staining and larval death suggests a cause and effect relationship between programmed cell death and larval death. Amino sugars that interfere with toxicity also interfere with the time course of acridine orange staining of larval polytene nuclei. The toxin first causes programmed cell death of anterior midgut and gastric caeca cells and, subsequently, posterior midgut cells. This pattern is similar to the temporal sequence of larval polytene cell death that occurs during metamorphosis. From the size and distribution of the nuclei that are stained with acridine orange, it appears that only polytene midgut cells are affected by toxin and that the diploid regenerative cell are not affected.

A Novel 29-kDa Crystal Protein fromBacillus thuringiensisInduces Caspase Activation and Cell Death of Jurkat T Cells

“…It is the paradigm for the mode of action of Cry proteins that they bind specific receptors on the epithelial cell membrane of the midgut of target insect larvae and are inserted into the membrane, resulting in colloid-osmotic swelling and lysis of the cell. 7,10) But induction of apoptosis by Cry proteins in mosquito larvae has been reported, 26) and A, Jurkat cells (1 Â 10 6 cells/ml) were treated with p29. Equal amounts of the nuclear extract prepared from 1 Â 10 6 cells of Jurkat were analyzed by SDS-8%-PAGE.…”

Specificity and Combinatorial Effects of Bacillus Thuringiensis Cry Toxins in the Context of GMO Environmental Risk Assessment

“…Instead the signal transduction model proposes that binding of Cry toxin monomers to cadherin activates an intracellular cell death mechanism (Smouse and Nishiura, 1997;Zhang et al, 2005Zhang et al, , 2006a. This model also has been questioned by Vachon et al (2012) and also by Soberón et al (2009) Zhang et al (2005Zhang et al ( , 2006a and the "sequential binding" model to be at work, and Kumar and Kumari (2015) consider both modes of action to act in a complementary fashion.…”

“…By comparison, modes of action of Cry 3 and Cry 2 toxins have received far less attention (Schnepf et al, 1998;Whalon and Wingerd, 2003;Vachon et al, 2012). Some authors think that specificity rests equally on the solubilization-activation process as on the receptor-binding and pore-formation process (Smouse and Nishiura, 1997), while others postulate specificity to rest mainly on (affinity to) specific receptors (Schnepf et al, 1998). Today, quite a controversy exists over the mode of action of Cry toxins which is owed to the fact that there is less scientific certainty about it today than there was when cry transgenes from B. thuringiensis were first engineered into GM plants roughly 30 years ago.…”

Impact of Antibiotics on Efficacy of Cry Toxins Produced in Two Different Genetically Modified Bt Maize Varieties in Two Lepidopteran Herbivore Species, Ostrinia nubilalis and Spodoptera littoralis

“…However, over the past 10 years, two more proposed models are debated: one, the sequential binding model, complementing the classical pore forming model by proposing additional steps such as cleavage of an alpha-helix and oligomerization prior to the pore formation, while the other challenges the formation of pores, or at least its absolute requirement in the process of cell lysis. Instead, it proposes a ‘signal transduction model’ where binding of Cry toxin monomers to cadherin activates intracellular cell death mechanisms [9,10,11]. The upregulation of caspase-4 transcripts [12] observed in Ostrinia nubilalis exposed to Cry1Ab may partly corroborate this pathway.…”