Original Article Stage-specific regulation of programmed cell death during oogenesis of the medfly Ceratitis capitata (Diptera, Tephritidae) ATHANASSIOS D. VELENTZAS, IOANNIS P. NEZIS, DIMITRIOS J. STRAVOPODIS, ISSIDORA S. PAPASSIDERI* and LUKAS H. MARGARITIS Faculty of Biology, Department of Cell Biology and Biophysics, University of Athens, Athens, Greece 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. KEY WORDS: apoptosis, autophagy, Ceratitis capitata, nurse cell, programmed cell death Introduction The egg chamber, or follicle, is the structural and functional unit of insect ovary. The egg chambers are formed in the anterior region of the ovary and they move towards the posterior pole as they develop during oogenesis. Thus, each ovariole contains an array of developmentally ordered egg chambers. In the meroistic polytrophic ovarioles of Drosophila melanogaster and Ceratitis capitata, each egg chamber consists of 16 germ line cells (15 nurse cells and 1 oocyte), surrounded by a monolayer of somatic epithelial cells, called follicle cells (Trougakos and Margaritis, 2002; Berg, 2005). The nurse cells support the development of the oocyte providing organelles, proteins and maternal RNAs to the oocyte through the ring canals (Mahajan-Miklos and Cooley, 1994; Trougakos and Margaritis, 2002). The development of the egg chamber has been divided into several discrete stages (fourteen according to King, 1970; twenty according to Margaritis, 1985; 1986). Int. J. Dev. Biol. 51: 57-66 (2007) doi: 10.1387/ijdb.062164av *Address correspondence to: Dr. Issidora S. Papassideri. Faculty of Biology, Department of Cell Biology and Biophysics, University of Athens, Panepistimiopolis 15784, Athens, Greece. Tel: +30-210-727-4546. Fax: ++30-210-727-4742. e-mail: ipapasid@biol.uoa.gr 0214-6282/2007/$30.00 © UBC Press Printed in Spain www.intjdevbiol.com Programmed cell death is an evolutionary conserved and genetically regulated process, where superfluous cells undergo self-destruction by activation of a cell suicide program (Danial and Korsmeyer, 2004). There are two major types of programmed cell death, apoptotic cell death (or type 1) and autophagic cell death (or type 2), both of which are defined by distinct morphological criteria. Apoptotic cell death is mainly characterized by nuclear condensation (pyknosis) and DNA fragmentation (karyorhexis), without major ultrastructural changes of cytoplasmic organelles. In the autophagy-mediated cell death, the major morphological feature is the accumulation of autophagic vacuoles in the cyto- plasm (Bursch, 2001; 2004; Lockshin and Zakeri, 2004). Apoptosis involves the regulated activation of caspases, a family of cysteine proteases that specifically recognize and cleave critical cellular target proteins, such as nuclear lamins and other structural Abbreviations used in this paper: FC, follicle cells; MDC, monodansylcadaverine stain; NC, nurse cell; NN, nurse cell nucleus; OC, oocyte.