Stage-specific regulation of programmed cell death during oogenesis of the medfly Ceratitis capitata (Diptera, Tephritidae)

Abstract

In the present study, we describe novel features of programmed cell death in developing egg chambers occurring during mid-and late-oogenesis of the medfly Ceratitis capitata. During mid-oogenesis, the spontaneously degenerated egg chambers exhibit typical characteristics of apoptotic cell death. Their nurse cells contain fragmented DNA and fragmented actin, as revealed by TUNEL assay and immunolabelling, respectively. In vitro caspase activity assays and immunostaining procedures demonstrated that the atretic egg chambers acquired high levels of caspase activity. Distinct features of autophagic cell death were also observed during C. capitata mid-oogenesis, as revealed by the monodansylcadaverine staining approach and ultrastructural examination performed by transmission electron microscopy. Additionally, atretic egg chambers exhibit an upregulation of lysosomal proteases, as demonstrated by a procathepsin L immunolabelling procedure. At the late stages of C. capitata oogenesis, apoptosis and autophagy coexist, manifesting cell death features that are similar to the ones mentioned above, being also chaperoned by the involvement of an altered cytochrome c conformational display. We propose that apoptosis and autophagy operate synergistically during C. capitata oogenesis for a more efficient elimination of the degenerated nurse cells and abnormal egg chambers.

Cell death duringDrosophila melanogasterearly oogenesis is mediated through autophagy

“…Moreover, autophagy could also act in parallel and cooperatively with caspases for the most efficient degradation of the tissue, as previously suggested. [39][40][41][42] In future studies we will try to identify molecular mechanisms that illuminate the contribution of autophagy in the cell death process.…”

Autophagy and its physiological relevance in arthropods: Current knowledge and perspectives

“…Egg chambers during stages 7-9 undergo cell death and contain degenerated nurse cells, characterized by caspase activation, chromatin condensation, DNA fragmentation, the formation of autophagosomes and autolysosomes and engulfment of nurse cell remnants by follicle cells. 81 This phenotype has been observed in Drosophilidae (D. melanogaster and Drosophila virilis), [88][89][90] in the Mediterranean fruit fly Ceratitis capitata, 91 in the olive fruit fly Dacus oleae 92 and in the mosquito with metamorphosis (Umemiya-Shirafuji R, et al unpublished data). 16 Although two caspase-like genes categorized as apoptosis initiators have been identified in H. longicornis, 60 the relationship between these putative caspases and the degradation of tick tissues remains uncertain.…”

“…Autophagy participates in this cell death process, functioning cooperatively with apoptosis for the most efficacious elimination of the degenerated nurse cells in several species. [89][90][91]105,108 Autophagy is also required for the degeneration of the follicular epithelium in a caspase-independent manner. 103,104 A very recent report by McCall's group reports that dying nurse cells of Drosophila show hallmarks of necrosis together with a cell-autonomous requirement of lysosomal DNase II activity.…”

“…77 Fourteen stages of oogenesis have been described of egg chambers. 83,86,[89][90][91] Although autophagy is suggested to promote cell death of individual cells in the egg chambers, the resources generated from cell death promote better conditions for the physiology of the ovary and the whole fly in general, finally resulting in cell survival. A similar example is the autophagic cell death of the salivary gland in Drosophila during metamorphosis, a life stage in which the fly does not eat and must develop adult structures in the absence of external nutrient resources.…”

“…Accordingly, degenerating mid-stage egg chambers in Drosophila and C. capitata are demonstrated to contain autophagosomes and autolysosomes. 83,86,[89][90][91] Furthermore, ATG1 and ATG7 mutants show a decrease in lysosomal staining and reduced levels of DNA fragmentation at midoogenesis, even though chromatin condensation in nurse cells still occurs normally. 83,84,86 These data suggest that autophagy can act upstream of DNA fragmentation during PCD in midoogenesis and also indicate that chromatin condensation is regulated independently from DNA fragmentation, as was shown before for late oogenesis.…”