Regulation of Stem Cell Self-Renewal and Differentiation

描述(申请人提供)：干细胞自我更新和分化的调节NIH 1 R01 GM080501成体干细胞在一生中需要补充分化的细胞和修复受损的组织。维持和控制成体干细胞群体的分子机制是利用成体干细胞用于再生医学的潜力以及了解癌症的起源和生物学的关键。我们建议研究与干细胞生态位局部环境的相互作用如何维持果蝇睾丸中的生殖系干细胞种群，这是一个在体内研究成体干细胞的强大系统。在之前的资金周期中，我们发现睾丸干细胞壁龛中的体细胞支持细胞提供了调节干细胞自我更新和分化的关键微环境，生殖系干细胞(GSCs)朝向这个壁龛建立了一个刻板的有丝分裂纺锤体，确保了GSC分裂的正常不对称结果。我们发现，来自体细胞中心的细胞因子样信号激活了GSCs及其配对的体细胞囊干细胞(CySCs)中的转录因子STAT，激活的STAT对于维持CySC的特性和GSC与中心的连接至关重要。CySCs是GSC生态位的重要组成部分，可以在远离中心的异位地点维持GSC。我们还发现生殖细胞需要来自体细胞囊细胞的“Go分化”信号，才能退出干细胞的无限增殖，进入有限的传递扩增(TA)分裂的精原程序，然后分化。这些发现突显了一个新的模型，即来自利基细胞的信号如何调节干细胞的自我更新，在该模型中，从干细胞到TA细胞的及时转换是由抵消自我更新和分化信号之间的平衡来安排的。我们现在建议利用我们已经建立的强大的系统和工具来识别调节干细胞行为的分子电路，以响应来自利基的线索。我们将研究GSC是如何附着和定位到中枢的，以及这种正常行为是如何通过激活转录因子STAT而被来自中枢的UPD信号控制的。我们将研究CySCs是否通过发出“自我更新”信号或阻断“Go分化”信号来维持GSCs，并测试候选信号机制和调节因子，以了解该利基如何调节干细胞的命运，以及同一利基内两种干细胞类型的行动如何协调。最后，我们将测试这样一个模型，即通过来自成囊细胞的信号激活体细胞内的EGFR下调CySC程序，允许在生殖系和体细胞谱系中及时从干细胞状态切换到祖细胞状态。 公共卫生相关性：拟议的研究结果将建立组织微环境如何调节成体干细胞自我更新和分化的范例，成体干细胞对人体内许多细胞类型的组织维持和修复至关重要。了解支持细胞是如何调控成人干细胞行为的，可能会解释肿瘤间质如何支持癌症干细胞，以及维持在正常环境中的干细胞如何通过来自支持细胞的信号触发分化来抑制不受控制的增殖。

DESCRIPTION (provided by applicant): Regulation of Stem Cell Self-renewal and Differentiation NIH 1 R01 GM080501 Adult stem cells are required throughout life to replenish differentiated cells and repair damaged tissue. The molecular mechanisms that maintain and keep in check adult stem cell populations are key for harnessing the potential of adult stem cells for regenerative medicine as well as understanding the genesis and biology of cancer. We propose to investigate how interactions with the local environment of the stem cell niche maintain populations of germ line stem cells in the Drosophila testis, a powerful system for study of adult stem cells in vivo in the context of their niche. In previous funding cycles, we discovered that somatic support cells in the testis stem cell niche provide a crucial microenvironment that regulates both stem cell self renewal and differentiation, and that germ line stem cells (GSCs) orient toward this niche to set up a stereotyped mitotic spindle, ensuring the normally asymmetric outcome of GSC divisions. We showed that a cytokine like signal from the somatic hub activates the transcription factor STAT in GSCs and their partner somatic cyst stem cells (CySCs) and that activated STAT is critical for maintenance of CySC identity and GSC attachment to the hub. CySCs are an important component of the GSC niche and can maintain GSCs in ectopic sites away from the hub. We also found that germ cells require a "go differentiate" signal from somatic cyst cells to exit limitless stem cell proliferation and enter the spermatogonial program of limited transit amplifying (TA) divisions then differentiation. These findings highlight a new model for how signals from the niche regulate stem cell self- renewal, in which timely transition from stem to TA cell is choreographed by a balance between counteracting self-renewal and differentiation signals. We now propose to utilize the powerful system and tools we have established to identify the molecular circuitry that regulates stem cell behavior in response to cues from the niche. We will investigate how GSCs attach to and orient toward the hub and how this normal behavior is controlled by the Upd signal from the hub through activation of the transcription factor STAT. We will investigate whether CySCs maintain GSCs by sending a "self renew" signal or blocking a "go differentiate" signal and test candidate signaling mechanisms and regulators to understand how the niche regulates stem cell fate and how the actions of two stem cell types within the same niche are coordinated. Finally, we will test the model that activation of the EGFR in somatic cyst cells by a signal from cystoblasts downregulates the CySC program, allowing a timely switch from stem cell to progenitor state in both the germ line and somatic lineages. PUBLIC HEALTH RELEVANCE: The results of the proposed studies will establish paradigms for how the tissue microenvironment regulates self-renewal and differentiation of adult stem cells, which are centrally important for tissue maintenance and repair for many cell types in the human body. Understanding how support cell niches regulate adult stem cell behavior may illuminate how tumor stroma support cancer stem cells and how stem cells maintained in their normal environment may be restrained from uncontrolled proliferation by signals from support cells that trigger differentiation.