CAREER: Emergence of Population Diversity from Stem Cell Decision Making in Asexual Planarians

职业：无性涡虫干细胞决策中种群多样性的出现

• 批准号: 1832823
• 负责人: Eva-Maria Collins
• 金额: $ 80.42万
• 依托单位: Swarthmore College
• 依托单位国家: 美国
• 项目类别: Continuing Grant
• 财政年份: 2018
• 资助国家: 美国
• 起止时间: 2018-03-01 至 2024-06-30
• 项目状态: 已结题
• 来源: https://www.nsf.gov/awardsearch/showAward?AWD_ID=1832823&HistoricalAwards=false
• 关键词: CAREER; Emergence; Population; Diversity; Stem

Diversity of individuals is indispensable for population survival and evolution. This CAREER project examines how diversity can emerge from decision making of individual cells in a multicellular regenerative organism. Freshwater planarians are famous for their regenerative capabilities that are based on a large number of adult pluripotent stem cells (ASCs). These ASCs allow them to reproduce by binary fission, thus creating a clonal population and raising the question of how this species is able to create sufficient diversity to survive on evolutionary time scales. Using tools from statistical physics the PI recently demonstrated that reproduction is largely random, but that reproductive patterns exist whose molecular and physical determinants remain to be investigated. This project aims at testing the hypothesis that population diversity arises from a joint effect of the specifics of planarian reproduction mechanics and epigenetic diversity of ASCs in individual worms. The PI will integrate the research objectives of this proposal into three educational initiatives, which focus on "learning through research" and long-term engagement of students: (1) The PI is establishing a partnership with Vista Magnet Middle school that allows 6th graders to work together with her lab on research projects throughout the school year. (2) The PI will continue her efforts toward participation of high school students in research. In particular, she will continue to enable students from Torrey Pines High School to engage in research in her lab throughout the year, which allows them to design and execute their own science projects. (3) The PI will continue her efforts in promoting undergraduate research, in her own group as well as through a new research-centered, quantitative biology laboratory course that she has developed. The course will launch in 2016 and is currently for incoming biology freshmen only. In the context of this proposal, the PI will widen the student population to physics freshmen by adding more physics to the curriculum, and thus create a truly interdisciplinary research-driven laboratory course at the interface of biology and physics in terms of content and student population.How cellular decision-making causes specific phenotypes in a population has received a lot of attention in the context of single celled organisms, but less is known about how epigenetic inheritance affects population diversity in multicellular organisms. This study will close this knowledge gap using planarians and a unique experimental setup, whereby thousands of individual reproductive events have already been recorded and form the statistical framework for the PI's studies on the population level. The PI's strategy is to (1) test the hypothesis that within individual planarians, ASCs are differentially distributed, in terms of spatial orientation and/or molecular and cellular characteristics (division and death rates, genetic and epigenetic diversity) through quantification of ASC localization, cellular dynamics, and single cell sequencing, (2) investigate the biomechanics of asexual reproduction to understand how resources get distributed among offspring using traction force measurements and time-lapse imaging, and (3) develop a mathematical model based on the cellular and organismal level experimental data to predict population level phenotypic diversity. The model will be tested by comparing its predictions with existing experimental data and the reproductive patterns of specially designed founder individuals in which all cells are known to originate from a single ASC, through RNA-seq and statistical analysis. Together, these approaches will allow the PI to test the hypothesis that spatial epigenetic heterogeneity of stem cells in individuals combined with a stochastic reproduction mechanism determine intraspecies phenotypic differences on the population level, which will be measured in terms of reproductive behaviors. The proposed work will shed new light onto the role of transgenerational epigenetic inheritance for the evolutionary success of asexual multicellular life. On a broader level, stem cell decision-making is currently receiving considerable attention because an understanding of how stem cells switch states stochastically and in response to environmental cues is indispensable for successful stem cell therapies.This project is being jointly supported by the Physics of Living Systems program in the Division of Physics and the Cellular Cluster in the Division of Molecular and Cellular Biosciences

个体的多样性是种群生存和进化的必要条件。这个CAREER项目研究了多样性如何从多细胞再生生物体中的单个细胞的决策中产生。淡水真涡虫以其基于大量成体多能干细胞（ASC）的再生能力而闻名。这些ASCs允许它们通过二分裂繁殖，从而创造了克隆种群，并提出了这个物种如何能够创造足够的多样性以在进化时间尺度上生存的问题。利用统计物理学的工具，PI最近证明了生殖在很大程度上是随机的，但生殖模式的存在，其分子和物理决定因素仍有待研究。该项目旨在验证种群多样性是由个体蠕虫中的真涡虫生殖机制和ASCs表观遗传多样性的具体特性共同作用而产生的假设。PI将把这项提案的研究目标整合到三项教育计划中，重点是“通过研究学习”和学生的长期参与：（1）PI正在与Vista Magnet中学建立合作伙伴关系，允许六年级学生与她的实验室一起工作，整个学年的研究项目。(2)PI将继续努力促进高中生参与研究。特别是，她将继续使学生从Torrey Pines高中全年在她的实验室从事研究，这使他们能够设计和执行自己的科学项目。(3)PI将继续努力促进本科生的研究，在她自己的小组，以及通过一个新的研究为中心，定量生物学实验室课程，她已经开发。该课程将于2016年推出，目前仅适用于即将入学的生物学新生。在这一提议的背景下，PI将通过在课程中增加更多的物理来将学生群体扩大到物理系大一新生，从而在内容和学生群体方面在生物学和物理学的界面上创建一个真正跨学科的研究驱动的实验室课程，细胞决策如何导致群体中的特定表型在单细胞生物的背景下受到了很多关注但是对于表观遗传如何影响多细胞生物的种群多样性却知之甚少。这项研究将使用Planarians和独特的实验设置来缩小这一知识差距，其中已经记录了数千个个体生殖事件，并形成了PI在种群水平上研究的统计框架。PI的策略是：（1）检验假设，即在个体的涡虫中，ASC在空间方向和/或分子和细胞特征方面存在差异（分裂和死亡率，遗传和表观遗传多样性）通过量化ASC定位，细胞动力学和单细胞测序，（2）研究无性繁殖的生物力学，利用牵引力测量和延时成像，了解资源如何在后代中分配，（3）根据细胞和生物体水平的实验数据建立一个数学模型来预测群体水平的表型多样性。该模型将通过将其预测与现有的实验数据以及专门设计的创始人个体的生殖模式进行比较来进行测试，其中所有细胞都已知来自单个ASC，通过RNA-seq和统计分析。总之，这些方法将允许PI检验以下假设：个体中干细胞的空间表观遗传异质性与随机生殖机制相结合，决定了种群水平上的种内表型差异，这将在生殖行为方面进行测量。这项工作将为跨代表观遗传在无性多细胞生命进化成功中的作用提供新的线索。在更广泛的层面上，干细胞决策目前正受到相当大的关注，因为了解干细胞如何随机转换状态并对环境线索做出反应是成功的干细胞治疗所不可或缺的。该项目由物理学系的生命系统物理学项目和分子与细胞生物科学系的细胞群共同支持