Abstract
BackgroundApoptosis is programmed cell death that ordinarily occurs in ovarian follicular cells in various organisms. In the best-studied holometabolous insect, Drosophila, this kind of cell death occurs in all three cell types found in the follicles, sometimes leading to follicular atresia and egg degeneration. On the other hand, egg development, quantity and viability in the mosquito Culex quinquefasciatus are disturbed by the infection with the endosymbiont Wolbachia. Considering that Wolbachia alters reproductive traits, we hypothesised that such infection would also alter the apoptosis in the ovarian cells of this mosquito. The goal of this study was to comparatively describe the occurrence of apoptosis in Wolbachia-infected and uninfected ovaries of Cx. quinquefasciatus during oogenesis and vitellogenesis. For this, we recorded under confocal microscopy the occurrence of apoptosis in all three cell types of the ovarian follicle. In the first five days of adult life we observed oogenesis and, after a blood meal, the initiation step of vitellogenesis.ResultsApoptoses in follicular cells were found at all observation times during both oogenesis and vitellogenesis, and less commonly in nurse cells and the oocyte, as well as in atretic follicles. Our results suggested that apoptosis in follicular cells occurred in greater numbers in infected mosquitoes than in uninfected ones during the second and third days of adult life and at the initiation step of vitellogenesis.ConclusionsThe presence of Wolbachia leads to an increase of apoptosis occurrence in the ovaries of Cx. quinquefasciatus. Future studies should investigate if this augmented apoptosis frequency is the cause of the reduction in the number of eggs laid by Wolbachia-infected females. Follicular atresia is first reported in the previtellogenic period of oogenesis. Our findings may have implications for the use of Wolbachia as a mosquito and pathogens control strategy.
Highlights
Apoptosis is programmed cell death that ordinarily occurs in ovarian follicular cells in various organisms
Half of all insect species are infected by Wolbachia [4,5,6], and several Brazilian populations of Culex quinquefasciatus are naturally infected by these bacteria [7]
General morphology of the ovaries Using confocal microscopy, we described the developmental patterns of ovaries during several moments of the oogenesis and vitellogenesis
Summary
Apoptosis is programmed cell death that ordinarily occurs in ovarian follicular cells in various organisms. In the best-studied holometabolous insect, Drosophila, this kind of cell death occurs in all three cell types found in the follicles, sometimes leading to follicular atresia and egg degeneration. Culex quinquefasciatus is a common house mosquito, and because they pierce the hosts’ skin to consume blood, they are a competent vector of neurotropic viruses, such as West Nile Virus and human and veterinary encephalitis viruses. They can transmit filarial worms and cause substantial nocturnal discomfort and allergic reactions [1]. The first is using cytoplasmic incompatibility for population substitution and control [9, 10], and the second is related to the influence of this bacterium on the replication of pathogens that infect the Almeida and Suesdek Parasites & Vectors (2017) 10:398 vector concomitantly, leading to non-transmission of the pathogen [8]
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