Occurrence of apocrine secretion in the larval gut epithelial cells of Aedes aegypti L., Anopheles albitarsis Lynch-Arribálzaga and Culex quinquefasciatus say (Diptera: Culicidae): a defense strategy against infection by Bacillus sphaericus Neide?

Abstract

Ocorrência de Secreção Apócrina nas Células Epiteliais do Intestino de Larvas de Aedes aegypti L.,Anopheles albitarsis Lynch-Arribálzaga e Culex quinquefasciatus Say (Diptera: Culicidae): um Mecanismo de Defesa contra Infecção Causada por Bacillus sphaericus Neide?RESUMO -Observou-se hipertrofi a das células do epitélio intestinal de Aedes aegypti (L.), Anopheles albitarsis (Lynch-Arribálzaga) e Culex quinquefasciatus (Say) devido ao aumento da atividade secretora intracelular como primeira reação às toxinas das linhagens 2362 e S1116 de Bacillus sphaericus (Neide). Após a hipertrofi a epitelial, formaram-se vesículas na porção apical das células, as quais eram compostas de fragmentos de membrana plasmática contendo material de natureza desconhecida em seu interior, caracterizando um tipo de secreção apócrina. A via de contaminação das larvas dos mosquitos por essas bactérias é pelo intestino, através da alimentação. Dependendo da espécie de Culicidade e da linhagem bacteriana utilizada, a hipertrofi a do epitélio ocorreu entre 5 a 15 min após a exposição das larvas ao meio contaminado. O segundo aspecto observado no processo de contaminação foi o aumento da atividade de secreção apócrina. As vesículas basófi las que se desprendiam das células permaneciam entre a membrana peritrófi ca e o lúmen intestinal. Observou-se atividade secretora tanto no grupo controle como no experimental, porém muito mais intensa no grupo experimental. Os Culicidae estudados apresentaram diferenças marcantes nas respostas às toxinas das bactérias utilizadas, sendo C. quinquefasciatus a espécie mais suscetível. As diferenças de reações das células em relação às toxinas produzidas pelas duas linhagens bacterianas são discutidas. PALAVRAS-CHAVE: Mosquito, controle biológico, virulênciaABSTRACT -Cell hypertrophy was the fi rst reaction of the gut epithelial cells of Aedes aegypti (L.), Anopheles albitarsis (Lynch-Arribálzaga) and Culex quinquefasciatus (Say) to the toxins of strains 2362 and S1116 of Bacillus sphaericus, as cells had an increase of intracellular secretory activity. Soon after the cell hypertrophy developed, vesicles were formed at the cell apical portion, which detached with the plasma membrane, characterizing a type of apocrine secretion like. The fi rst pathway of contamination of the mosquito larvae by these bacteria is through the gut, by feeding. Depending on the species of Culicidae and on the bacterial strain used, the hypertrophy of the gut epithelium occurred between 5 and 15 min after exposure to the contaminated environment. The second aspect observed after hypertrophy was the increase in apocrine secretion. The basophilic vesicles that detached from the cells remained between the peritrophic membrane and the gut lumen, such vesicles were fi lled with material of unknown nature. The gut posterior region showed secretory activity in both control and treated larvae, being much more intense in bacteria-exposed larvae. There were remarkable differences in the epithelial cell reaction according to the toxins of the ...

Histological and Histochemical Characterization of the Midgut of Healthy Aedes aegypti Larvae

“…Only the lateral caeca are evident in deeper sections, and among them, one can see the remaining structures. The gastric caeca cells are large, slightly flattened, with clear edges along the brush border, which contrasts with the description by [18] who suggested that these cells did not have well-developed microvilli ( Fig. 4).…”

Enterocyte Purge and Rapid Recovery Is a Resilience Reaction of the Gut Epithelium to Pore-Forming Toxin Attack

“…Rather, our findings indicate that limited cytoplasmic extrusion accounts for the thinning of the epithelium. Cytoplasmic extrusion in the insect larval gut in response to ingested bacteria has previously been reported and, in some cases, referred to as apocrine secretion (Oliveira et al, 2009;Vodovar et al, 2005). However, since ultrastructural studies did not reveal membrane surrounding the extruded cytoplasm (this work; Vodovar et al, 2005), this latter term may not be appropriate.…”

Isolates of Bacillus thuringiensis from Maranhão biomes with potential insecticidal action against Aedes aegypti larvae (Diptera, Culicidae)

“…This result is consistent with data from Rey et al (1998) and Cavados et al (2004) that identified these characteristics as determinants of the toxic action of Bt species and the subsequent death of the susceptible host. However, after 6 h of exposure, we still observed the initial toxic action of the BtMA-179 isolate in the intestine of A. aegypti larvae, and the high production of digestive vesicles observed suggests an attempt at defence by the insect against the bacterial action (Oliveira et al, 2009).…”

“…The morphological changes in intestinal epithelial cells of A. aegypti larvae caused by Bt isolates were evaluated according to Oliveira et al (2009), with modifications. The assays were performed using groups of 10 third-instar larvae from a colony kept at an average temperature of 26 ± 2 °C, a relative humidity of 85% and a photophase of 12 h in the Medical Entomology Laboratory.…”

“…The presence of cry and cyt genes can be used to predict the insecticidal activity of a novel isolate. Due to the complexity of the action of δ-endotoxins, it is also necessary to assess the frequency of the genes involved in larval mortality and to understand the mode of action of these proteins in larval intestinal cells (Cavados et al, 2004;Oliveira et al, 2009;Soberón et al, 2018).…”