Regulation of stem cell differentiation during Drosophila oogenesis

描述（由申请人提供）：干细胞自我更新的丧失导致维持器官的失败，并可能导致退行性疾病。相反，分化的丧失会导致癌症。因此，在退行性疾病中防止过早分化的能力，或在癌症中诱导分化的能力，将对治疗产生巨大的影响。我们的长期目标是确定控制从干细胞自我更新到分化的关键调控途径，使用果蝇种系干细胞（GSCs）作为模型系统。生殖细胞是终极的干细胞，因为它们既具有全能性又具有长生不老性。因此，在生殖系中建立的范例可以扩展到其他干细胞系统。由于突变体、标记物、RNAi技术和靶向表达方法的可用性，果蝇是研究干细胞自我更新和分化问题的优越模型系统。在果蝇胚胎发生过程中，由基因极性颗粒组分（pgc）介导的全局转录沉默保守过程在生殖细胞分化中起着关键作用。在缺乏pgc的情况下，生殖细胞表现出早熟的转录，导致体细胞基因的转录，从而导致其死亡。在卵发生过程中，在分化过程中，卵母细胞命运从GSC命运被指定。我们发现，在卵子发生过程中，Pgc在GSC的分化子代中短暂表达，Pgc的缺失会导致分化缺陷。我们认为，在卵发生过程中，Pgc介导的转录沉默抑制了来自周围生态位细胞的自我更新信号的反应，并促进了GSC子细胞的分化。为了验证这一假设，我们将(1)确定转录沉默子Pgc如何促进GSC分化；(2)明确GSC分化过程中Pgc的靶点及作用机制；(3)探讨pgc在卵子发生过程中的调控机制。我们的工作将为临时工确立一个角色

DESCRIPTION (provided by applicant): Loss of stem cell self-renewal results in failure to maintain organs and can lead to degenerative disorders. In contrast, loss of differentiation can lead to cancers. Thus, the ability to prevent premature differentiation in degenerative diseases, or to induce differentiation in case of cancer, will have tremendous therapeutic impact. Our long-term goal is to determine key regulatory pathways that control the transition from stem cell self-renewal to differentiation, using Drosophila germline stem cells (GSCs) as a model system. The germ cells are the ultimate stem cells as they are both totipotent as well as immortal. Thus, paradigms established in the germ line can be extended to other stem cell systems. Drosophila is a superior model system to study questions about stem cell self-renewal and differentiation because of the availability of mutants, markers, RNAi technology and targeted expression methods. In Drosophila embryogenesis, the conserved process of global transcriptional silencing, mediated by the gene polar granule component (pgc), plays a pivotal role in germ cell specification. In absence of pgc, germ cells show precocious transcription that result in the transcription of somatic genes leading to their death. During oogenesis, an oocyte fate is being specified from a GSC fate during the process of differentiation. We have discovered that during oogenesis, Pgc is transiently expressed in the differentiating daughter of the GSC and loss of pgc results in differentiation defects. We propose that during oogenesis, Pgc mediated transcriptional silencing acts to suppress the response to self-renewal signaling from the surrounding niche cells and promotes differentiation in the GSC daughter. To test this hypothesis we will (1) Determine how the transcriptional silencer, Pgc, promotes GSC differentiation; (2) Identify Pgc targets and the mechanism of action during GSC differentiation; (3) Investigate how pgc is regulated during oogenesis. Our work will establish a role for transient transcriptional silencing in reprogramming stem cell fate by demonstrating that Pgc in the GSC daughter is expressed in a cell cycle dependent manner and determining a requirement for Pgc to promote efficient differentiation. We favor the idea that transcriptional silencing is needed to "clear" residual stem cell factors, thereby reprogramming the GSC daughter prior to differentiation. Based on findings from this application, we posit that transcriptional silencing could be a potent target for increasing efficiency in deriving stem cells and also as a target in cancer treatment.