A similar phenotype was also observed when was knocked down by RNAi specifically in stretch follicle cells, demonstrating that was non-autonomously required for nurse cell removal

A similar phenotype was also observed when was knocked down by RNAi specifically in stretch follicle cells, demonstrating that was non-autonomously required for nurse cell removal. targets to eliminate the cell.5 In addition to apoptosis, many other forms of cell death have been described. However, a molecular understanding of these forms of cell death has lagged significantly compared to apoptosis. Other forms of cell death, including necrosis, pyroptosis, and undoubtedly others, are likely to contribute significantly to certain human diseases, and identifying treatments hinges on a molecular understanding of these alternative cell death pathways.6 For example, necroptosis has recently been associated with multiple sclerosis, 7 and pyroptosis occurs in response Platycodin D to bacterial or viral contamination.5,7 Distinct biochemical requirements for different forms of cell death have been identified (see 6,8,9 for reviews). While apoptosis is typically considered a form of cell suicide, apoptosis and other forms of cell death Platycodin D can be controlled non-autonomously, via either assisted suicide or murder. 10 TNF-induced necroptosis and apoptosis are well-characterized examples of assisted suicide, where signaling downstream of death receptors determines the form of cell death that occurs.7 Natural killer T cells can also induce apoptosis non-autonomously Platycodin D by releasing granzyme B, which cleaves caspase substrates and triggers the caspase cascade.11 Entosis is an intriguing form of cell death where one cell commits suicide by invading another cell, and requires the lysosomal machinery of the surrounding cell for its degradation.12 When cells die, they are typically phagocytosed and degraded by another cell. However, in some instances phagocytic cells actively participate in the death of the target cells.13 This was first demonstrated in when engulfment mutants showed increased survival of cells that had compromised caspase activity.14,15 More recently, it has been shown that a surrounding phagocytic cell affects caspase levels and activity in the precursor of a dying cell.16 In another recent example in ovary.19-21 Each egg is derived from a germline cyst of 16 Platycodin D cells, where one cell differentiates as the oocyte and the other 15 cells become polyploid nurse cells. At the end of oogenesis during stages 10-11, the 15 nurse cells transfer their cytoplasm to the oocyte and then during stages 12-14, the nurse cell nuclei are degraded. Genetic studies have ruled out a major role for apoptosis in developmental nurse cell death.20-23 Mutants of caspase genes or the apoptosis initiators, and mutant ovaries and found that there was a profound effect on developmental nurse cell death.27 Whereas wild-type egg chambers showed an average of 0.2 nurse cell nuclei remaining by stage 14, mutants had an average of 8 persisting nurse cell nuclei. A similar phenotype was also observed when was Igf1 knocked down by RNAi specifically in stretch follicle cells, demonstrating that was non-autonomously required for nurse cell removal. Knockdown of another engulfment gene, and the ortholog have been shown to function in parallel.33 To determine whether this held true in the stretch follicle cells, we generated double knockdowns. Indeed, double mutants showed a stronger phenotype with over 10 persisting nuclei, suggesting that and function in parallel during nurse cell death. We screened through a number of other engulfment genes using RNAi and identified several other genes important for nurse cell removal (and the JNK pathway). The persistence of nurse cell nuclei could indicate a defect in clearance, or a defect in cell death.27 To distinguish between these possibilities, we stained ovaries for several cell death markers. In wild-type ovaries, signs of nurse cell death first become apparent in stage 10B, when nurse cell nuclei become permeable, releasing nuclear proteins such as the reporter nuclear ?-galactosidase.34 Cytoplasmic actin bundles also form during stage 10B, prior to the rapid transfer of nurse cell cytoplasm to the oocyte.34 After the transfer of cytoplasm in stage 11, nurse cell nuclei become more compact, and eventually become acidified and stain positively for TUNEL (Terminal deoxynucleotidyl transferase dUTP nick end labeling) 23,24,35,36 which labels the 3OH groups of fragmented DNA. We found that TUNEL and acidification were almost completely abolished in mutants.27 While nurse cell dumping was not affected, the leakage of nuclear proteins was impaired. Together these findings indicated that the nuclei remained intact in mutants, suggesting that nurse cell death as well as clearance was inhibited. Stretch follicle cells control nurse cell death To directly address Platycodin D the requirement of stretch follicle cells in nurse cell death, we eliminated them by expressing RNAi against the caspase inhibitor specifically in the stretch follicle cells.27 We found that these egg chambers not only had persisting nuclei, but they were also dumpless, indicating that there was a failure in the transport of nurse cell cytoplasm to the oocyte. Actin bundles failed to form in the cytoplasm, and the nurse cell nuclei failed to become acidified or TUNEL-positive. These findings demonstrate that the stretch follicle cells control all aspects of nurse cell death. Moreover, it shows.