melanogaster w1118 [23]. In our view, the
electron-dense Linsitinib order structures, which we revealed at the periphery of region 1 of the germarium, are presumably autophagosome encapsulated dying Wolbachia. A supporting line of evidence came from Wright and Barr [37], who on the basis of their observations on degenerating germaria cysts from mosquitoes Aedes scutellaris suggested that these structures represented degenerating Wolbachia. Cell fragments containing dying bacteria and autophagosomes and appearing as numerous smaller puncta in regions 2a/2b and 1 of the germarium may represent autophagy, not apoptosis. This appears plausible when recalling that AO stains not only apoptotic cells, also lysosomes [38]. TUNEL did not reveal such puncta in these regions. The possible role of the Wolbachia strain wMelPop in programmed cell death in region 2a/2b of the germarium Our current estimates of apoptosis in region 2a/2b of the germarium from the ovaries of the uninfected D. melanogaster w1118T raised on standard food are consistent with those reported elsewhere [14]. It is of interest that apoptosis level in the germaria decreased in D. melanogaster w1118T , but not XMU-MP-1 in D. melanogaster Canton ST after transfer to rich food. This may be indicative of differences in sensitivity to changes in food composition between different fly stocks. AO- and TUNEL staining demonstrated that the virulent Wolbachia strain wMelPop increased
the percentage of germaria containing apoptotic cells in D. melanogaster w1118 ovaries, while wMel strain was without such an effect. The effect of wMelPop on cystocytes in ovaries was observed in flies maintained on standard and rich food. Evidence was provided that the effect of Wolbachia on D. melanogaster is not general, nearly being rather specific to the pathogenic strain wMelPop. What pathways may be envisaged for the Wolbachia strain wMelPop caused increase in the number
of germaria whose cysts undergo apoptosis? On the one hand, bacteria may have a direct effect on germline cells (Figure 7A, B). In fact, one of 16 cyst cells becomes the oocyte, the other 15 differentiate into nurse cells in region 2a of the germarium. This is associated with transport of 15 centrioles into the pre-oocyte, where the microtubule-organizing center forms [39, 40]. Wolbachia distribution is dependent upon microtubules during oogenesis and bacteria show mislocalization in the egg chambers treated with colchicine which causes depolymerization of microtubules [41]. Evidence has been obtained indicating that Wolbachia are evenly distributed throughout the MK-8776 oocyte and nurse cells during stages 1-2 of oogenesis, becoming concentrated at the oocyte anterior during stages 3-6 [41]. With this in mind, the high levels of Wolbachia in cystocytes during differentiation into oocyte and nurse cells in region 2a of the germarium may possibly lead to impairment at the structural and/or molecular level, the cyst may undergo apoptosis as a consequence (Figure 7B).