FlexAggon · Evolutionary origin of cell adhesion: the basis of multicellularity in the choanoflagellate Choanoeca flexa

How animal multicellularity evolved from unicellular ancestors remains an open evolutionary question. One key pre-requisite for the evolution of animal multicellularity was the evolution of cell adhesion. However, little is known about how cell adhesion evolved in the animal stem. In the last decades, considerable advances to reconstruct early animal evolution have come from investigations of the closest living unicellular relatives of animals, notably the choanoflagellates. These microeukaryotes have become powerful models to address the evolution of animals, for several reasons: (1) they are the sister group to all animals; (2) their genomes encode homologs of genes that can inform about animal origins, including an animal-like “cell-adhesion toolkit”; (3) they can temporarily adhere to each other and form multicellular colonies; and (4) they are amenable to functional genetics. Therefore, studies on choanoflagellate molecular and cell biology can inform the mechanisms of the emergence of multicellularity in animals. Here, I will investigate the cell adhesion mechanisms governing multicellularity in the recently discovered choanoflagellate Choanoeca flexa. C. flexa has direct cell-cell adhesion and aggregative multicellularity (unique in choanoflagellates) and also undergoes light-controlled collective contractility of colonies (unique in unicellular relatives of animals), making it a powerful model to study the emergence of collective behaviors. I will perform a systematic characterization of the environmental and endogenous factors regulating cell adhesion during colony formation in C. flexa using a combination of genetic engineering, biochemistry, proteomics, molecular and cell biology approaches, and functional genomics. The data generated here will contribute to converting C. flexa into an experimentally tractable species and has the potential to shed light on the pre-metazoan function of cell adhesion genes.