The merger that made us

[...]the origin of eukaryotes is best depicted as a point of fusion on the tree of life (see large arrow on Fig. 1). Whereas outside-in models assume that the plasma membrane remained in place during the evolution of eukaryotes, with the nuclear compartment arising from the coalescence of internalized membranes, the inside-out model posits that the inner nuclear membrane marks the boundary of the original archaeal host, with the endomembrane system and plasma membrane forming later as a result of the fusion of extracellular protrusions (see Fig. 2). Furthermore, there is no evidence of archaea undergoing a process akin to endocytosis, which frequently relies on the activity of Dynamin, a protein that eukaryotes appear to have acquired from the mitochondrial symbiont [10]. [...]it seems clear that full-blown eukaryotic vesicle trafficking arose only after the archaeal eukaryotic ancestor established a close and stable association with a bacterial partner from which it acquired lipids and other, mainly metabolic, genes (see fusion point in Fig. 1). [...]there is a real chance of identifying other intermediates in stable partnerships with proteobacteria that might represent sister groups that are even closer to eukaryotes than Lokiarchaeota (depicted by a “?” in Fig. 1). [...]while we now know so much more about the origin of eukaryotes than we did in 2014, fleshing out the details remains a thrilling prospect for the years ahead. 1.