Stem Cell Niche Positioning in the Germ Line of C. elegans

干细胞对多细胞生物的正常发育和组织稳态至关重要。分裂干细胞的分化子细胞形成所需的组织，而自我更新的子细胞保留其干细胞特性。干细胞生态位提供了调节干细胞自我更新和分化平衡的信号，并建立了对这种平衡进行适当调节至关重要的空间组织。生态位的位置是确保细胞在适当的时间和适当的位置分化的关键。在线虫生殖系中，生态位是位于生殖腺臂末端的远端尖端细胞（DTC）。我们将利用我们的发现，编码保守的Derlin蛋白的cup-2的缺失，导致DTC从性腺的远端转移到性腺臂的更近端。在最极端的DTC移位病例中，当DTC从远端移动了10-15个生殖细胞直径时，干细胞群也会移动到紧邻移位的DTC的新位置。为了了解维持DTC在适当位置的机制，我们将首先确定DTC形态的变化是否有助于cup-2突变体位移表型。DTC包括短突和长突，以及一个神经丛，它围绕着紧邻DTC的细胞。我们将比较cup-2突变体与野生型动物中这些过程的数量和长度，以及神经丛的大小。cup-2突变体中DTC形态的变化可能表明这些结构在维持生殖腺远端DTC中起作用。接下来我们将确定cup-2在DTC粘附中的作用。已知CUP-2/Derlin蛋白在内质网相关蛋白降解（ERAD）中起作用。因此，为了确定茶杯-2突变体中的DTC位移是否由于ERAD的破坏，我们将分析内质膜应力被化学诱导或其他ERAD成分功能减少或消除时的DTC位移。如果通过化学物质或突变体破坏ERAD不会导致DTC位移，那么这可能表明cup-2具有参与DTC粘附的ERAD独立功能。最后，我们将利用cup-2突变体作为起点，确定维持生殖腺远端DTC的其他因素。由于在cup-2突变体中观察到的位移是不完全渗透的，因此进行增强子突变筛选以确定其他因素是一个理想的遗传背景。执行这种筛选并描述确定的因素将是我实验室的长期重点。确定小生境细胞定位是如何被控制的对于我们理解干细胞自我更新和分化是如何被精确控制以允许适当的发育和组织稳态是至关重要的。

Stem cells are essential for proper development and tissue homeostasis in multicellular organisms. Differentiating daughters of dividing stem cells form the desired tissue, while self-renewing daughter cells retain their stem cell character. The stem cell niche provides the signal that regulates the balance between stem cell self-renewal and differentiation, and establishes the spatial organization that is critical for this balance to be properly regulated. The position of the niche is key to ensuring that cells differentiate at the proper time and in the proper location. In the C. elegans germ line the niche is the Distal Tip Cell (DTC), which is at distal end of each gonad arm. We will exploit our discovery that loss of cup-2, which encodes a conserved Derlin protein, results in the DTC becoming displaced from the distal end of the gonad to a more proximal location along the gonad arm. In the most extreme cases of DTC displacement where the DTC has moved ~10-15 germ cell diameters from the distal end, the stem cell population also moves to this new location immediately adjacent to the displaced DTC. In order to understand the mechanisms involved in maintaining the DTC at its proper location, we will first determine if changes in DTC morphology contribute to the cup-2 mutant displacement phenotype. The DTC contains both short and long processes, as well as a plexus that surrounds cells immediately adjacent to the DTC. We will compare the numbers and lengths of these processes, as well as the size of the plexus, in cup-2 mutants with those found in wild-type animals. A change in DTC morphology in cup-2 mutants could suggest a role for these structures in maintaining the DTC in the distal end of the gonad. Next we will determine cup-2's role in DTC adhesion. CUP-2/Derlin proteins are known to function in Endoplasmic Reticulum Associated Protein Degradation (ERAD). Therefore, to determine if DTC displacement in a cup-2 mutant is due to a disruption in ERAD we will analyze DTC displacement when ER stress is chemically induced, or when the functions of other ERAD components are reduced or eliminated. If disrupting ERAD through chemicals or mutants does not result in DTC displacement, then this could suggest that cup-2 has an ERAD independent function that is involved in DTC adhesion. Finally, we will utilize the cup-2 mutant as a starting point to identify additional factors involved in maintaining the DTC in the distal end of the gonad. Since the displacement observed in cup-2 mutants is incompletely penetrant, it is an ideal genetic background to perform an enhancer mutant screen to identify additional factors. Performing this screen and characterizing the identified factors will be a long-term focus of my lab. Determining how niche cell positioning is controlled is essential for us to understand how stem cell self-renewal and differentiation are precisely controlled to allow for proper development and tissue homeostasis.