LTREB: The Multicellularity Long Term Evolution Experiment (MuLTEE)

The origin of multicellular life stands among the most significant evolutionary innovations in Earth's history, enabling the emergence of complex organisms and ecological relationships that transformed our planet's biosphere. While there has been progress in understanding this important biological transition that occurred millions of years ago, the exact processes that allowed single cells to aggregate into complex organisms composed by different cell types and differentiated tissues (as seen in most plants and animals), remain unclear. Becoming multicellular brings a series of new challenges, for example reduced nutrient accessibility to individual cells that can easily lead to cell death and the need for fundamental tasks to be divided across different cells. Using yeast as a model system, this project will investigate the genetic, molecular, and physiological steps involved in transitioning from existing as single cells into complex cell aggregates, that gave rise to the multitude of life forms present today. This research will provide crucial insights into the origin of complex life, as well as shed light into the processes involved in major biological transitions. This project will create a web portal that will facilitate the sharing of strains, data, and detailed methodological protocols that will facilitate the use of the yeast system by the broader community and the general public. It will also provide yeast evolution kits to high school and college classrooms, providing unique opportunities for students to witness and document evolution in action. The Multicellularity Long Term Evolution Experiment (MuLTEE) will provide a powerful approach to investigate the transition between single- and multi-celled life forms. It will evolve multicellularity in real-time through laboratory selection for increased organismal size in initially unicellular Saccharomyces cerevisiae yeast populations. Since the experiment's inception in 2018, these "snowflake yeast" have evolved from microscopic cell clusters into increasingly integrated organisms that are visible to the naked eye, developing remarkable innovations including entangled cellular architectures that distribute mechanical forces throughout the organism, differentiated cell types with specialized functions, and coordinated developmental programs. This grant supports the experiment's essential daily operations—particularly the daily transfers required for continued evolution, long-term cryopreservation of the full experiment, and collection of core genomic and phenotypic data. 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.