Induction of Manduca sexta Larvae caspases expression in midgut cells by Bacillus thuringiensis Cry1Ab toxin

Abstract

Bacillus thuringiensis produces 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 the caspases expression by RT-PCR analysis, showing that the initial response of Manduca sexta midgut 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-3 mRNA 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. © 2011 Helena Porta et al.