Abstract
Bacillus thuringiensisproduces crystal toxins known as Cry that are highly selective against important agricultural and human health-related insect pests. Cry proteins are pore-forming toxins that interact with specific receptors in the midgut cell membrane of susceptible larvae making pores that cause osmotic shock, leading finally to insect death. In the case of pore-forming toxins that are specific to mammalian cells, death responses at low doses may induce apoptosis or pyroptosis, depending on the cell type. The death mechanism induced by Cry toxins in insect midgut cells is poorly understood. Here, we analyze thecaspasesexpression by RT-PCR analysis, showing that the initial response ofManduca sextamidgut cells after low dose of Cry1Ab toxin administration involves a fast and transient accumulation of caspase-1 mRNA, suggesting that pyroptosis was activated by Cry1Ab toxin as an initial response but was repressed later. In contrast,caspase-3mRNA requires a longer period of time of toxin exposure to be activated but presents a sustained activation, suggesting that apoptosis may be a cell death mechanism induced also at low dose of toxin.
Highlights
Bacillus thuringiensis (Bt) are insecticidal Gram-positive bacteria that produce inclusion bodies composed by δendotoxin proteins, during sporulation [1]
The aim of our work was to explore if pyroptosis and apoptosis cell response processes, are activated in vivo in the midgut cells of Manduca sexta larvae in response to Cry1Ab intoxication
Our results suggest that M. sexta midgut cells may induce first pyroptosis as an initial response to low doses of toxin, and apoptosis is triggered later with a more sustained pattern at low toxin dose
Summary
Bacillus thuringiensis (Bt) are insecticidal Gram-positive bacteria that produce inclusion bodies composed by δendotoxin proteins, during sporulation [1]. The main components of these inclusions are the crystal (Cry) toxins, which possess highly selective toxicities against important agricultural and human health-related insect pests but are nontoxic to mammals or other organisms [2]. PFTs are important virulence factors that kill eukaryotic cells by different mechanisms, depending on the dose and the cell type (for review, see [4]). Cell death occurs through two different mechanisms: (1) apoptosis, characterized by the activation of initiatorcaspases (Cas) (Cas-2, -4, -8, -9, -10, and -12) that trigger effector-Cas (Cas-3, -6, and -7) to cleave cellular substrates. Apoptotic cells features include nuclear and cytoplasmic condensation and cellular fragmentation, Cas-3 activation, DNA damage, and formation of apoptotic bodies [5] and (2)
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