Mechanisms of Steroid-Triggered Programmed Cell Death

小分子亲脂激素通过其相应的核受体作用于高等生物体，控制着广泛的发育和生理反应。虽然广泛的研究集中在核受体控制靶基因转录的机制上，但对激素信号如何在发育过程中转化为适当的生物反应知之甚少。我们建议以果蝇为模型系统，详细定义一种这样的途径--类固醇触发的细胞死亡。众所周知，类固醇在控制包括人类在内的高等生物体中的细胞死亡方面发挥着核心作用。然而，只有在果蝇身上，才发现了与荷尔蒙相关的遗传级联 对死亡的反应--在变态过程中，由于类固醇激素蜕皮激素的作用，幼虫的唾液腺遭到破坏。我们建议在此基础上，使用开放式遗传筛选来识别这一途径中的关键角色。通过使用GFP作为活体动物唾液腺的标记，我们将识别在类固醇触发的死亡反应中显示特定缺陷的突变。一个试点屏幕已经证明了这种方法的可行性。我们确定了死亡途径中的已知基因以及几个新的参与者，包括编码CBP转录辅助因子和TBP相关因子的基因， TRF2.我们建议详细描述这两个基因，定义它们与细胞死亡之间的联系机制。我们还建议通过对大约40%的基因组进行饱和突变来扩大我们对死亡调节因子的搜索。突变将被映射到特定的基因，并分配这些基因的功能。这项工作为理解激素信号转导的分子机制提供了基础-定义了将荷尔蒙与发育过程中阶段和组织特定的生物反应联系起来的遗传级联中的参与者。这项工作也代表了首次尝试使用随机突变来解剖果蝇的内源性程序性细胞死亡反应，这增加了我们发现新的死亡调节因子的可能性。最后，我们的研究为确定类固醇如何控制人类细胞死亡提供了基础，对理解和治疗人类疾病具有重要意义。

Small lipophilic hormones, acting through their corresponding nuclear receptors, control a wide range of developmental and physiological responses in higher organisms. Although extensive studies have focused on the mechanisms by which nuclear receptors control target gene transcription, relatively little is known about how a hormonal signal is transduced into an appropriate biological response during development. We propose to define one such pathway in detail - steroid-triggered cell death - using Drosophila as a model system. It is well known that steroids play a central role in controlling cell death in higher organisms, including humans. Only in Drosophila, however, has a genetic cascade been identified that links the hormone to a death response - the destruction of the larval salivary glands in response to the steroid hormone ecdysone during metamorphosis. We propose to build off this foundation, using an open-ended genetic screen to identify key players in this pathway. By using GFP as a marker for salivary glands in living animals, we will identify mutants that show specific defects in the steroid-triggered death response. A pilot screen has demonstrated the feasibility of this approach. We identified known genes in the death pathway as well as several new players, including genes that encode the CBP transcriptional co-factor and the TBP-related factor, TRF2. We propose to characterize these two genes in detail, defining the mechanisms that link them to cell death. We also propose to expand our search for death regulators through saturation mutagenesis of approximately 40% of the genome. Mutations will be mapped to specific genes, and functions for these genes will be assigned. This work provides a basis for understanding the molecular mechanisms of hormone signal transduction - defining the players in a genetic cascade that link the hormone to a stage- and tissue-specific biological response during development. This work also represents the first attempt to use random mutagenesis to dissect an endogenous programmed cell death response in Drosophila, raising the possibility that we will uncover novel death regulators. Finally, our studies provide a foundation for determining how steroids control cell death in humans, with implications for understanding and treating human disease.