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: 1555109
• 负责人: Eva-Maria Collins
• 金额: $ 85万
• 依托单位: University of California-San Diego
• 依托单位国家: 美国
• 项目类别: Continuing Grant
• 财政年份: 2016
• 资助国家: 美国
• 起止时间: 2016-07-15 至 2018-04-30
• 项目状态: 已结题
• 来源: https://www.nsf.gov/awardsearch/showAward?AWD_ID=1555109&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

个体的多样性对于种群的生存和进化是不可或缺的。这个职业项目研究了多细胞再生生物中单个细胞的决策是如何产生多样性的。淡水涡虫以其基于大量成体多能干细胞（ASCs）的再生能力而闻名。这些ASCs允许它们通过二元裂变繁殖，从而产生无性繁殖种群，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最近证明了繁殖在很大程度上是随机的，但繁殖模式的存在，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产生于涡虫生殖机制和个体蛔虫ASCs表观遗传多样性共同作用的假设。PI将把该提案的研究目标整合到三个教育举措中，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，允许六年级学生在整个学年中与她的实验室一起进行研究项目。(2) PI将继续努力促进高中生参与研究。特别是，她将继续让来自多利松高中的学生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将继续努力推动本科研究，在她自己的小组中，以及通过她开发的新的以研究为中心的定量生物学实验课程。该课程将于2016年启动，目前仅面向即将入学的生物学大一新生。在此提案的背景下，PI将通过在课程中添加更多的物理来扩大物理新生的学生群体，从而在内容和学生群体方面创建一个真正的跨学科研究驱动的实验课程，在生物学和物理学的界面上。在单细胞生物的背景下，细胞决策如何引起群体中的特定表型受到了很多关注，但对于表观遗传如何影响多细胞生物的群体多样性知之甚少。这项研究将利用涡虫和一个独特的实验装置来弥补这一知识差距，在这个实验装置中，数千个个体的繁殖事件已经被记录下来，并形成了PI在种群水平上研究的统计框架。PI的策略是：(1)通过ASC定位、细胞动力学和单细胞测序的量化，验证在单个涡虫中，ASC在空间方向和/或分子和细胞特征（分裂和死亡率、遗传和表观遗传多样性）方面分布差异的假设；(2)利用引力测量和延时成像研究无性生殖的生物力学，了解资源如何在后代之间分配；(3)基于细胞和有机体水平的实验数据建立数学模型，预测种群水平的表型多样性。通过RNA-seq和统计分析，将该模型的预测结果与现有的实验数据和专门设计的创始个体的生殖模式进行比较，以检验该模型，其中所有细胞都已知来自单个ASC。总之，这些方法将允许PI测试假设，即干细胞在个体中的空间表观遗传异质性与随机生殖机制相结合，决定种群水平上的种内表型差异，这将通过生殖行为来测量。这项工作将揭示跨代表观遗传在无性多细胞生命进化成功中的作用。在更广泛的层面上，干细胞决策目前受到相当多的关注，因为了解干细胞如何随机切换状态并响应环境线索是成功的干细胞治疗不可或缺的。该项目由物理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集群共同支持