Exploring cell type differentiation in the Filasterean Capsaspora Owczarzaky by single-cell RNA-seq

Trabajo presentado en el Moscow Forum PROTIST 2016, celebrado en Moscú del 6 al 10 de junio de 2016.The origin of multicellular animals from their unicellular ancestors is one of the most important evolutionary transitions in life’s history. However, the specific cellular and genetic changes that led to this transition remain unknown. Phylogenomic analyses have shown that animals are closely related to three unicellular lineages: choanoflagellates, filastereans and ichthyosporeans, altogether forming the Holozoa clade. Recent phylogenomic studies have shown that those premetazoan taxa already had a complex repertoire of genes important for multicellularity, some of them previously thought to be exclusive of animals. Different versions of “simple multicellularity” are found among the unicellular relatives of Metazoa. There is the clonal development of colonial choanoflagellates, the aggregative behavior of Capsaspora owczarzaki, and the coenocytic development of ichthyosporeans. Those colonies and aggregates are assumed to be without cell differentiation. However, there is no molecular data proving that all cells within those colonies or aggregates or coenocytes are identical. Here we show microscopic evidence for the coexistence of different cell types in C. owczarzaki aggregates. We also show our advances in developing single-cell transcriptomics methodology in these organism to molecularly characterize cell types. The possibility of analyzing differential gene expression at the single-cell level between diverse cell types of unicellular holozoans will allow us to better understand the molecular mechanisms underlying programs of cell differentiation in the origin of animals. The aggregates of C. owczarzaki offer us an ideal model in which to test this, and provide a better framework to understand the origin of the different metazoan cell types.N