Co-option of cell cycle regulation for multicellular evolution

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The evolution of multicellularity is a major transition in organismal form. However, the genetic basis of multicellularity, in any group of organisms, is not well understood. This project will utilize multicellular green algae as model eukaryotes that have undergone the most recent known example of multicellular evolution. One member, Volvox, often appear in undergraduate texts and in museums as prime examples of multicellular evolution. Despite the importance of multicellular evolution for life on Earth, the genetic basis of multicellularity in any of these organisms is unknown. The goal of this project is to address this fundamental gap in our knowledge of multicellular evolution by examining how the cell cycles of these organisms have evolved for multicellularity. Broader Impact activities will include the training of young scientists from underrepresented groups along with first generation college students.The central hypothesis of this project is that cell cycle regulation from unicellular Chlamydomonas has been co-opted to evolve multicellularity in its undifferentiated multicellular relative Gonium. Previous experiments show that the retinoblastoma (RB) cell cycle repressor from Gonium, when expressed in unicellular Chlamydomonas, causes Chlamydomonas to become multicellular suggesting that evolutionary co-option of cell cycle regulation is important for the evolution of multicellularity. Two approaches will be used to test the central hypothesis. First, how RB control of the cell cycle has evolved from unicellular Chlamydomonas to undifferentiated multicellular Gonium will be determined to identify genes that are differently regulated by RB in Gonium compared to Chlamydomonas. Second, candidate multicellularity genes in Gonium identified from the first approach and from comparative genomics will be functionally tested for gain-of-function in Chlamydomonas and by loss-of-function in Gonium. In sum, from a combination of approaches, this project will advance our understanding of genetic determinants of multicellular evolution.