Actin cytoskeleton reorganization of the apoptotic nurse cells during the late developmental stages of oogenesis in Dacus oleae

In the present study, we demonstrate the actin cytoskeleton reorganization during nurse cells apoptosis of the olive fruit fly Dnc lts oleae. At the d evelopmental stage 9A of oogenesis, the actin microfilaments are assembled in numerous ring canals and subcortically support all the nurse cells, as i s shown by phalloidin-FITC staining. During the following stages, 9B and 10 A, this structural pattern remains the same. The developmental stage 10B is characterized by actin microfilament rearrangement and formation of actin cables that are symmetrically organized around the nurse cell nuclei. At st age II, when the dumping process begins, these actin cables seem to retain each nurse cell nucleus in the cell center, away from blocking the ring can als. The early stage 12 is characterized by an asynchronous nurse cell nucl ear chromatin condensation, while at late stage 12 the actin cables become very thick, as adjacent ones overlap one another and traverse the disorgani zed apoptotic nurse cell nuclei that already have fragmented DNA, as is dem onstrated by acridine orange staining and TUNEL assay. Finally, during stag e 13, the apoptotic nuclear remnants are phagocytosed by the neighboring fo llicle cells. The data presented herein compared to previous reported resul ts in Drosophila [Nezis et al., 2000. Eur J Cell Biol 79:610-620], demonstr ate that actin cytoskeleton reorganization during nurse cell apoptosis is a developmentally regulated physiological mechanism, phylogenetically conser ved in higher Dipteran. (C) 2001 Wiley-Liss. Inc.