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

Georgia Tech Research Corporation, Atlanta GA

Investigators

Abstract

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.