Abstract
BackgroundWolbachia are bacterial endosymbionts of many arthropod species in which they manipulate reproductive functions. The distribution of these bacteria in the Drosophila ovarian cells at different stages of oogenesis has been amply described. The pathways along which Wolbachia influences Drosophila oogenesis have been, so far, little studied. It is known that Wolbachia are abundant in the somatic stem cell niche of the Drosophila germarium. A checkpoint, where programmed cell death, or apoptosis, can occur, is located in region 2a/2b of the germarium, which comprises niche cells. Here we address the question whether or not the presence of Wolbachia in germarium cells can affect the frequency of cyst apoptosis in the checkpoint.ResultsOur current fluorescent microscopic observations showed that the wMel and wMelPop strains had different effects on female germline cells of D. melanogaster. The Wolbachia strain wMel did not affect the frequency of apoptosis in cells of the germarium. The presence of the Wolbachia strain wMelPop in the D. melanogasterw1118 ovaries increased the number of germaria where cells underwent apoptosis in the checkpoint. Based on the appearance in the electron microscope, there was no difference in morphological features of apoptotic cystocytes between Wolbachia-infected and uninfected flies. Bacteria with normal ultrastructure and large numbers of degenerating bacteria were found in the dying cyst cells.ConclusionsOur current study demonstrated that the Wolbachia strain wMelPop affects the egg chamber formation in the D. melanogaster ovaries. This led to an increase in the number of germaria containing apoptotic cells. It is suggested that Wolbachia can adversely interfere either with the cystocyte differentiation into the oocyte or with the division of somatic stem cells giving rise to follicle cells and, as a consequence, to improper ratio of germline cells to follicle cells and, ultimately, to apoptosis of cysts. There was no similar adverse effect in D. melanogaster Canton S infected with the Wolbachia strain wMel. This was taken to mean that the observed increase in frequency of apoptosis was not the general effect of Wolbachia on germline cells of D. melanogaster, it was rather induced by the virulent Wolbachia strain wMelPop.
Highlights
Wolbachia are bacterial endosymbionts of many arthropod species in which they manipulate reproductive functions
Frequency of apoptosis in germaria from ovaries of the uninfected and Wolbachia-infected D. melanogaster Two parts are distinguished in the Drosophila ovariole: the germarium made up of four regions (1, 2a, 2b, 3) and the vitellarium (Figure 1A, B) [27,28]
The region 2a/2b, where apoptosis can occur, contains 16-cell cysts, somatic stem cells (SSCs), which contact with the somatic stem cell niche (SSCN) and follicle cells (Figure 1B)
Summary
Wolbachia are bacterial endosymbionts of many arthropod species in which they manipulate reproductive functions. The distribution of these bacteria in the Drosophila ovarian cells at different stages of oogenesis has been amply described. A checkpoint, where programmed cell death, or apoptosis, can occur, is located in region 2a/2b of the germarium, which comprises niche cells. We address the question whether or not the presence of Wolbachia in germarium cells can affect the frequency of cyst apoptosis in the checkpoint. A form of programmed cell death, is a process needed for normal development and maintenance of tissue homeostasis in multicellular organisms [1,2]. In the Drosophila melanogaster ovaries, there are two checkpoints where programmed cell death occurs. It is noteworthy that apoptosis and autophagy coexist at all the above mentioned stages of oogenesis in D. melanogaster [13,14]
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