Single-cell amplified genomes of uncultured choanoflagellates shed light into animal origins. Single-cell genomes of uncultured Choanoflagellates

Understanding the origins of animal multicellularity is a fundamental biological question. Recent genome data has unraveled the role that co-option of pre-existing genes played in the origin of animals. However, there was also some important genetic novelties at the onset of Metazoa. To have a clear understanding of the specific genetic innovations and how they appeared, we need broader taxon sampling possible, especially among early-branching animals and their unicellular relatives. Here, we take advantage of single-cell genomics to expand the genomic diversity of choanoflagellates, the sister-group to animals. With these genomes, we have performed an updated and taxon-rich reconstruction of protein evolution from the Last Eukaryotic Common Ancestor (LECA) to animals. Our novel data re-defines the origin of some genes previously thought to be metazoan-specific, like the POU transcription factor, which we show appeared earlier in evolution. Moreover, our data indicate that the acquisition of new genes at the stem of Metazoa was mainly driven by duplications and protein domain rearrangements processes at the stem of Metazoa. Furthermore, our analysis allowed us to reveal essential protein domains to maintain animal multicellularity. Our analyses also demonstrate the utility of single-cell genomics from uncultured taxa to address evolutionary questions.