Collaborative Research: Beta-catenin Regulation during Asymmetric Stem Cell Divisions

了解单细胞受精卵(受精卵)是如何发育成具有多样化、相互联系和适当指定组织的多细胞动物的，是我们理解动物(包括人类)实际工作方式的核心。发育生物学中最伟大的发现工具之一是小型线虫--秀丽线虫。利用这种生物体中可用的遗传工具，线虫生物学家这个庞大的国际社区在解释支配所有动物功能的细胞和发育机制方面取得了很大进展。例如，现在已经知道，相同的细胞通讯途径控制着不同物种的发育，包括线虫，以及像老鼠和人类这样的哺乳动物。这个合作项目调查了其中一个保守的途径在线虫发育中的作用，重点是不对称的干细胞分裂。它将把这些研究扩展到干细胞群体中最成熟的哺乳动物例子--肠道干细胞。通过这种方式，它将决定现有的线虫干细胞分裂控制模式在哺乳动物中的保守程度。因此，这项研究将提供一个强有力的框架，以解决这些远亲动物的干细胞遇到的共同问题。该项目将通过以下方式扩大这些研究的影响：1)通过面向普通公众的实践研讨会提高公众参与度和科学素养；2)通过将来自爱荷华州拥有大量拉美裔人口的农村社区的8年级学生带到校园进行一天的职业模拟，招募下一代STEM科学家；3)通过扩大本科研究机会，包括向弱势群体和代表性不足的群体提供研究机会，留住现有的STEM本科生。不对称细胞分裂(ACD)决定了动物从哺乳动物到线虫的细胞命运。这些生物中的干细胞使用ACD产生分化的子代和新的干细胞。WNT信号是一种保守的调节ACD和细胞命运的信号，它通过控制转录激活因子β-连环蛋白。本项目的目标是通过分析线虫β-连环蛋白-1的调控，阐明在不对称干细胞分裂过程中β-连环蛋白的调节机制，并开始在哺乳动物中测试由此产生的机制。线虫非常适合于这些分析，因为它的遗传和分子工具，活体ACD成像，将β-连环蛋白的信号和黏附功能分离到不同的基因，以及最近的研究发现，sys-1受到β-连环蛋白破坏复合体的同系物：Axin，APC和CK1pha的负调控。哺乳动物的肠道隐窝可以说是Wnt控制的干细胞维持的最著名的例子，它将被用来测试Sys1调节机制的保守，并将为蠕虫模型提供信息。该项目将确定Axin定位破坏复合体的机制，以及破坏复合体对细胞核中β-连环素的调节被保守到什么程度。这些研究的结果预计将为发育中细胞命运的指定和Wnt途径诱导的ACD在组织内稳态中的作用提供广泛重要的见解。

Understanding how a single-celled zygote (the fertilized egg) develops into a multicellular animal with diverse, interconnected and properly-specified tissues is core to our understanding of how animals, including humans, actually work. One of the great discovery tools in developmental biology is the small nematode, Caenorhabditis elegans. Taking advantage of the available genetic tools in this organism, the large international community of C. elegans biologists, has made great strides in explaining the cellular and developmental mechanisms that govern how all animals function. For instance, it is now known that the same cell communication pathways control the development of diverse species, including C. elegans, and mammals like mice and humans. This collaborative project investigates the role of one of these conserved pathways in C. elegans development, focusing on asymmetric stem cell divisions. It will extend these studies to the most well-established mammalian example of a stem cell population, intestinal stem cells. In this way, it will determine the extent to which existing models of control of C. elegans stem cell divisions are conserved in mammals. Thus the research will provide a strong framework to address common problems that stem cells in these distantly-related animals encounter. The project will broaden the impact of these studies by 1) increasing public engagement and science literacy through hands-on workshops geared toward the general public, 2) recruiting the next generation of STEM scientists by bringing 8th graders from rural Iowa communities with large Hispanic populations to campus for a day of career simulations and 3) retaining current STEM undergraduates by extending undergraduate research opportunities, including to disadvantaged and underrepresented groups. Asymmetric cell division (ACD) drives cell fate specification in animals from mammals to nematodes. Stem cells in these organisms use ACD to generate a differentiated daughter and a new stem cell. Wnt signaling is a conserved regulator of ACD and cell fate through its control of the transcriptional activator beta-catenin. The goal of this project is to elucidate the mechanisms of beta-catenin regulation during asymmetric stem cell divisions by analyzing regulation of the C. elegans beta-catenin, SYS-1, and to begin testing the resulting mechanisms in mammals. C. elegans is well-suited for these analyses because of its genetic and molecular tools, in vivo ACD imaging, the separation of the signaling and adhesion functions of beta-catenin into distinct genes and because of recent findings that SYS-1 is negatively regulated by homologs of the beta-catenin destruction complex: Axin, APC and CK1alpha. The mammalian intestinal crypt, arguably the best-known example of Wnt-controlled stem cell maintenance, will be used to test conservation of SYS 1 regulatory mechanisms and will also inform the worm models. This project will determine the mechanism by which Axin localizes the destruction complex, and the extent to which destruction complex regulation of beta-catenin in the nucleus is conserved. The results of these studies are predicted to provide broadly important insight into developmental cell fate specification and the role of Wnt pathway-induced ACD in tissue homeostasis.