Each experiment was done with three replicates of at least 20 animals each

Each experiment was done with three replicates of at least 20 animals each. The original description of thehs-rprtransgene reported that two developmental stages–the late embryo and the late pupae–were not sensitive to killing byreaper(White et al., 1996). apoptotic genes. This steroid-controlled switch defines a novel, physiologically-regulated, mechanism for controlling sensitivity to apoptosis and provides new insights into the control of apoptosis during development. Keywords:apoptosis, apoptosome-dependent, apoptosome-independent, ecdysone, mid-L3 transition, sensitivity to apoptosis == INTRODUCTION == The ability to commit suicide by apoptosis is a fundamental, and irreversible, cellular process in multicellular organisms. Accordingly, normal development and homeostasis depend on precise control over when and where apoptosis occurs. Apoptosis is regulated by a signaling cascade of cysteine proteases called caspases (Fuentes-Prior and Salvesen, 2004). Initiator caspases sit at the top of the signaling cascade; they exist as monomers and are activated by dimerization on specialized signaling platforms (Bratton and Salvesen, 2010). One such signaling platform, the apoptosome, is composed of oligomers of the caspase adaptor Apaf-1 and the initiator caspase Caspase-9 (Bratton and Salvesen, 2010). Unlike initiator caspases, effector caspases exist as inactive dimers and are activated by caspase-dependent proteolytic cleavage (Riedl and Shi, 2004). Although caspases are expressed in all cells, their inappropriate activation is prevented by Inhibitor of Apoptosis Proteins (IAPs) (Orme and Meier, 2009;Salvesen and Duckett, 2002). Activation of apoptosis during development is regulated by relieving the IAP-dependent inhibition of caspases. This mechanism is best elucidated inDrosophilawhere the activation of caspases converges on transcription of the IAP-antagonistsreaper,hidand/orgrim(Steller, 2008). These IAP-antagonists bind to Diap1 (DrosophilaIAP 1), disrupting its interaction with caspases and initiating caspase activation and apoptosis (Ryoo et al., 2002;Yoo et al., 2002). Elimination of all three IAP-antagonists blocks apoptosis, while ectopic expression triggers apoptosis (Chen et al., 1996;Grether et al., 1995;White et al., 1994;1996). Similarly, loss ofdiap1has been shown to result in immediate activation of apoptosis in embryos (Goyal et al., 2000;Lisi et al., 2000;Wang et al., 1999). The mammalian death activatorSmac/Diabloacts as an IAP-antagonist, inhibiting IAPs such as Survivin and XIAP, demonstrating that this pathway has been conserved through evolution (LaCasse et al., 2008). Apoptosis is executed when the rapidly expanding cascade Rabbit polyclonal to ABHD14B of caspase activation crosses a critical threshold; cells that do not cross this apoptotic threshold do not initiate apoptosis (Thompson, 1995). In turn, the ability to achieve this apoptotic threshold is predetermined by the endogenous expression levels of critical pro- and anti-apoptotic Medroxyprogesterone factors (Florentin and Arama, 2012;Lowe et al., 2004). This threshold model for activation of apoptosis was formulated primarily through characterization of oncogenic mutations and changes in gene expression observed in tumor cells, changes that disable the ability to trigger apoptosis in malignant cells (Adams and Cory, 2007;Lowe et al., 2004). It is now well established that the ability to evade apoptosis is a hallmark of cancer (Hanahan and Weinberg, 2011). However, physiological contexts for changes in the ability to trigger apoptosis and the mechanisms that regulate them remain poorly understood. Here, we characterize a dramatic and global switch in the sensitivity to apoptosis duringDrosophiladevelopment at the onset of metamorphosis and demonstrate that this switch, mediated by changes in expression of critical pro-apoptotic genes, is regulated by the steroid hormone 20-hydroxyecdysone (hereafter referred to as ecdysone). == MATERIALS AND Medroxyprogesterone METHODS == == Stocks == The following stocks were obtained from the BloomingtonDrosophilaStock Center:hs-Gal4,UAS-rpr,en-Gal4,UAS-RFP,Sgs3-Gal4,Sgs3-GFP,nub-Gal4, UAS-GFP,UAS-EcRF645AandNc51. The following stocks were kindly provided by colleagues in the fly community:hs-rpr(White et al., 1996),hs-hid(Grether et al., 1995),hs-diap1 RNAi(Yin and Thummel, 2004),Ark82(Akdemir et al., 2006) anddrice1(Muro et al., 2006). == Developmental staging == Early and wandering third instar larvae (eL3 and wL3, respectively) were identified by developmental age, wandering behavior and expression of a mid-L3-specific reporter (Sgs3-GFP)(Biyasheva et al., 2001). To collect eL3 animals, embryos were aged at 25C about Medroxyprogesterone 7688 hours after egg lay (AEL) and Sgs3-GFP-expressing larvae, if any, were removed. The wL3 animals were collected as rapidly wandering larvae from the sides of un-crowded bottles with robust expression of Sgs3-GFP (these animals are within 10 hours from puparium formation). Sugar feeding experiments were performed at 25C on agar plates with 20% sucrose and without yeast. == Delivery Medroxyprogesterone of apoptotic activators and survival assays == To trigger apoptosis in a temporally-controlled manner, we used transgenic.