Stem Cell Renewal and Differentiation in Spermatogenesis

描述（由申请人提供）：对指导干细胞行为的电路有浓厚的兴趣。虽然小生境对于许多组织特异性干细胞的行为是必不可少的，但尚不清楚小生境是如何在组织中指定和组装的，以及它如何控制干细胞库。了解这些相互作用对于在再生医学中使用这些细胞至关重要。这个建议解决了如何小生境指定，组织和功能，并利用最好理解的干细胞小生境系统之一，果蝇睾丸。在这里，一小群细胞（枢纽细胞）作为生态位的一部分，导致相邻细胞中信号通路的激活。以这种方式，附近的体细胞承担囊肿干细胞命运（CySC），而与这些CySC混合的附近的生殖系细胞承担生殖系干细胞命运（GSC）。枢纽的形成和干细胞的附着是性腺发生的主要结构事件。中枢细胞在体细胞性腺前体（SGP）中的指定和放置产生了一个前部锚定的增殖中心，该中心将以极化方式驱动精子发生。为了产生这种极性，前枢纽细胞的子集迁移通过形成性腺的生殖细胞环境，并经历间充质到上皮的转变（MET），然后才充当小生境细胞。最后，关键的自我更新信号由从枢纽细胞和CySC表达的BMP递送。第一个目的是使用活成像和功能丧失和获得的研究相结合，探索细胞骨架控制前枢纽细胞迁移，和间充质上皮过渡所需的生态位形成。第二个目标集中在Zfh1，一种转录调节因子，它是CySC自我更新的关键，也是CySC如何作为GSC更新的小生境细胞的关键。Zfh1的靶点将被鉴定和功能分析。这将定义对于CySC自我更新、对于GSC的更新信号的产生以及对于MET的控制重要的基因。

DESCRIPTION (provided by applicant): There is intense interest in the circuits that guide stem cell behavior. While niches are essential to the behavior of many tissue-specific stem cells, it is not understood how the niche is specified and assembled in a tissue, and then how it executes control over the stem cell pool. Understanding these interactions will be crucial to use these cells in regenerative medicine. This proposal addresses how are niches specified, organized and function, and utilizes one of the most well-understood stem cell-niche systems, the Drosophila testis. Here, a small group of cells (hub cells) act as part of the niche, leading t the activation of signaling pathways in adjacent cells. In this way, nearby somatic cells take on cyst stem cell fate (CySC), while nearby germline cells, intermingled with these CySCs, take on germline stem cell fate (GSC). Hub formation, and the attendant attachment of stem cells, is the major architectural event of gonadogenesis. The specification and placement of hub cells among somatic gonadal precursors (SGPs) generates an anteriorly-anchored proliferation center that will drive spermatogenesis in a polarized manner. To generate that polarity, a subset of pre-hub cells migrates through the germ cell milieu of the forming gonad, and undergoes a mesenchymal-to-epithelial transition (MET), only then acting as niche cells. Finally, the key self-renewal signal is delivered by BMPs expressed from both hub cells and CySCs. The first Aim uses a combination of live-imaging and loss- and gain-of-function studies to explore cytoskeletal control of pre-hub cell migration, and the mesenchymal-to-epithelial transition necessary for niche formation. A second Aim focuses on Zfh1, a transcriptional regulator which is key to CySC self- renewal and to how CySCs act as niche cells for GSC renewal. Targets of Zfh1 will be indentified and analyzed functionally. This will define genes important for CySC self- renewal, for the production of renewal signals for GSCs, and for the control of MET.