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无法维持器官，并可能导致退行性疾病。相反，分化的丧失可能导致癌症。因此，在退行性疾病中防止过早分化或在癌症的情况下诱导分化的能力将具有巨大的治疗影响。我们的长期目标是确定关键的调控途径，控制从干细胞自我更新到分化的过渡，使用果蝇生殖干细胞（GSC）作为模型系统。生殖细胞是最终的干细胞，因为它们既全能又永生。因此，在生殖系中建立的范例可以扩展到其他干细胞系统。果蝇是研究干细胞自我更新和分化问题的一个上级模型系统，因为突变体、标记、RNAi技术和靶向表达方法的可用性。在果蝇胚胎发育过程中，由基因极性颗粒成分（pgc）介导的保守的转录沉默过程在生殖细胞特化中起着关键作用。在缺乏pgc的情况下，生殖细胞表现出早熟转录，导致体细胞基因的转录导致其死亡。在卵子发生过程中，卵母细胞的命运是由分化过程中的GSC命运指定的。我们已经发现，在卵子发生过程中，Pgc在GSC的分化子代中瞬时表达，并且Pgc的缺失导致分化缺陷。我们建议，在卵子发生过程中，PGC介导的转录沉默行为，以抑制周围的小生境细胞的自我更新信号的反应，并促进分化的GSC女儿。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）确定GSC分化过程中Pgc的靶点和作用机制;（3）研究卵子发生过程中Pgc如何调节。我们的工作将建立一个角色， 通过证明GSC子代中的Pgc以细胞周期依赖性方式表达并确定Pgc促进有效分化的需要，来确定在重编程干细胞命运中的转录沉默。我们支持这样的观点，即转录沉默是必要的， “清除”残留的干细胞因子，从而在分化之前重编程GSC子代。基于这项应用的发现，我们认为转录沉默可能是提高干细胞衍生效率的有效靶点，也可以作为癌症治疗的靶点。

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.