Phylogenetic analysis of Centralspindlin and Ect2 provides mechanistic insights into the emergence of Metazoa and multicellularity

Obligate multicellularity evolved at least 5 times in eukaryotes, including at the origin of Metazoa [1, 2]. However, the molecular events leading to the acquisition of multicellularity are not understood in any lineage. Here, I present an integrated analysis into the contemporaneous emergence of three regulators of cytokinesis and the Metazoan kingdom. Phylogenetic and computational structural analyses indicate that the simultaneous presence of three key regulators of cytokinesis, Kif23, Cyk4, and Ect2 is Metazoan-specific. Structurally, these proteins are highly conserved across all Metazoa. These cytokinetic regulators link the plane of cell division with the position of the spindle during anaphase and subsequently nucleate assembly of stable intercellular bridges [3–6], structures prevalent in Metazoan germlines [7]. Furthermore, certain Choanoflagellates and more basal amoeboid species, some of which exhibit incomplete cytokinesis, encode divergent orthologs of these regulators. These findings, in conjunction with prior knowledge, suggests that evolutionary refinement of these three cytokinetic regulators directly contributed to the evolution of Metazoan multicellularity and germline development.