CAREER: Examining the Role of Nascent Multicellular Life Cycles on the Evolution of Organismal Complexity

多细胞生物的进化在生命史上反复发生，每次都导致新的更复杂的生命形式，如植物和动物。然而，关于单细胞生物如何进化形成多细胞群体，以及这些群体如何随后进化成复杂的、整合的多细胞个体，人们知之甚少。这些问题之所以持续存在，是因为这些转变已经深入到过去。该项目通过一种新的实验酵母系统克服了这一限制，并直接在实验室中研究多细胞性的进化。利用合成生物学，该团队将构建一种能够表达所有可能的早期多细胞生命周期的酵母菌株：单细胞阶段，聚集性多细胞阶段和克隆发育的多细胞阶段。该项目研究了表达这些不同生命周期的酵母如何在实验室中经过数千代进化，研究了多细胞进化所必需的两个关键步骤：相互依赖的细胞和细胞分化的起源。利用这种独特的实验系统和现代细胞生物学的强大工具，该项目将对多细胞起源产生根本性的见解。在进行上述实验的同时，该团队将寻求一个基础广泛的教育推广平台，向儿童、高中生、本科生/研究生和对科学有好奇心的成年人解释重大进化转变的神奇和优雅。这将主要通过开发新的高中和大学课程，举办讲习班来培训教师如何使用这些材料，并针对普通读者编写书籍来实现。最近的实验表明，单细胞生物很容易进化形成多细胞簇，但对细胞簇如何随后进化出更大的多细胞复杂性知之甚少。拟议的研究直接解决这个问题，使用雪花酵母模型系统，通过提出以下问题：细胞如何被剥夺其进化自主性，从生物体进化成新的多细胞生物体的相互依赖的部分？新的细胞分化是如何产生的？可以具体的生命周期（即，专性克隆发育）催化上述性状的进化？相反，这些过程是否因包括其他共同的生命史阶段而受到破坏（即，延长的单细胞期或聚集）？该项目将解决这些问题与酵母菌株工程表达不同的生命周期，如上所述，然后允许进化多代。现代细胞生物学的工具，如合成生物学，单细胞RNA-seq和3D共聚焦显微镜，将使研究团队能够跟踪进化动力学并表征这些谱系中的特定变化。对上述问题的探讨将为多细胞生物的进化起源提供基本的见解，并为其他主要进化转变的类似研究提供理论基础。该职业奖的教育目标有三个主要组成部分：i）开发，传播和支持雪花酵母实验室套件用于高中和大学课程。PI还将每月举办夏季教师培训讲习班，从主要是非洲裔美国人的亚特兰大公立学校招聘教师，并为高中教师听众举办讲座。ii）在格鲁吉亚理工学院开发一门新课程“复杂生命的起源：从细胞到社会”，并帮助为研究生生物物理学课程创建一个为期三周的雪花酵母模块。（三）通过书籍接触广大读者。PI将写两本关于主要进化转变的书，一本针对儿童（~5-8岁）的图画书和一本针对成人读者的书。该奖项反映了NSF的法定使命，并通过使用基金会的智力价值和更广泛的影响审查标准进行评估，被认为值得支持。

The evolution of multicellular organisms has occurred repeatedly over the history of life and in each case led to new more complex life forms, such as plants and animals. Yet, little is known about how single celled organisms evolve to form multicellular groups, and how these groups subsequently evolve into complex, integrated multicellular individuals. These questions persist because these transitions are deep in the past. This project overcomes this limitation with a novel experimental yeast system and directly examines the evolution of multicellularity in the lab. Using synthetic biology, the team will construct a yeast strain capable of expressing all possible early multicellular life cycles: a single-celled stage, an aggregative multicellular stage, and a clonally-developing multicellular stage. The project examines how yeast expressing these different life cycles evolve, over thousands of generations in the lab, examining two key steps necessary for the evolution of multicellularity: the origins of interdependent cells and cellular differentiation. Using this unique experimental system and the powerful tools of modern cell biology, this project stands to make fundamental insights into the origins of multicellularity. In parallel to the experiments described above, the team will pursue a broad-based educational outreach platform, explaining the wonder and elegance of major evolutionary transitions to children, high school students, undergrad/graduate students, and scientifically-curious adults. This will be accomplished primarily by developing novel high school and college curricula, holding workshops to train teachers how to use this material, and writing books aimed at a general audience.Recent experiments have shown that unicellular organisms readily evolve to form multi-celled clusters, but little is known about how cellular clusters subsequently evolve greater multicellular complexity. The proposed research addresses this subject directly, using the snowflake yeast model system, by asking the following questions: How are cells stripped of their evolutionary autonomy, evolving from organisms into mutually-reliant parts of the new multicellular organism? How does novel cellular differentiation arise? Can specific life cycles (i.e., obligate clonal development) catalyze the evolution of the above traits? Conversely, are these processes undermined by the inclusion of other common life history stages (i.e., an extended single-cell phase or aggregation)? The project will address these questions with yeast strains engineered to express different life cycles, as detailed above, and then allowed to evolve over many generations. The tools of modern cell biology, such as synthetic biology, single cell RNA-seq, and 3D confocal microscopy, will allow the research team to follow the evolutionary dynamics and characterize specific changes in these lineages. Answering the above questions will provide fundamental insight into the evolutionary origins of multicellularity and will provide a theoretical foundation for similar investigations in other major evolutionary transitions. The educational aims for this CAREER award have three major components: i) Develop, disseminate and support snowflake yeast lab kits for use in high school and college courses. The PI will also host monthly summertime teacher training workshops, recruiting teachers from predominantly African American Atlanta public schools, and give talks to audiences of high school teachers. ii) Develop a novel course 'Origin of Complex Life: from Cells to Societies' at Georgia Tech, and help create a three-week snowflake yeast module for a graduate-level biophysics course. iii) Reach a general audience through books. The PI will write two books on major evolutionary transitions, a picture book aimed at children (~5-8 years old) and a book for an adult audience.This award reflects NSF's statutory mission and has been deemed worthy of support through evaluation using the Foundation's intellectual merit and broader impacts review criteria.