Exploring cell type differentiation in unicellular holozoans by single-cell RNA-seq

SEBASTIÁN R. NAJLE; LINAS MAZUTIS; IÑAKI RUIZ-TRILLO

Heidelberg

Simposio; EMBO-EMBL Symposium: A new age of discovery for aquatic microeukaryotes; 2016

European Molecular Biology Organization (EMBO-EMBL)

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 genome data from choanoflagellates, the filasterean Capsaspora owczarzaki and the ichthyosporean Creolimax fragrantissima 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 observed in Capsaspora owczarzaki, and the multinucleate syncytium of the ichthyosporeans. Those colonies and aggregates are assumed to be without cell differentiation. However, there is no molecular data to proof that all cells within the colonies or the aggregates or the syncytium are identical. In this regard, we here show our advances in developing single-cell transcriptomics methodology in these organisms to address this question. The possibility of analyzing differential gene expression at the single-cell level between the diverse cell types that characterize the life cycles of the unicellular holozoans will allow us to better understand the molecular mechanisms underlying the programs of temporal cell differentiation that preceded spatial 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.