Origin of the Eukaryotic cell

“The origin and evolution of eukaryotes” is a tale that has yet to be told. At this point in time, it exists only as the title of a fascinating new compendium that has just been produced by the Cold Spring Harbor Press. While this volume is some 400 pages long, there is a palpable feeling among its authors that if they could somehow just compact it into a few pages, a figure, and perhaps even a token energy equation, then what is now just a diffuse description would become the explanation we seek—maybe even without any new discoveries or information.

The nearest the book comes to providing that holy explanation is undoubtedly the chapter by Thomas Cavalier-Smith dealing with what he likes to call the “Neomuran Revolution,” which we will describe below. At its heart, what Cavalier-Smith offers is a sweeping tree of life that has continued to grow with the abundant fertilizer he has added over the last several decades. Incidentaly, we should add that one of the best ways to expedite your ascendance to prominance in the origin of life business is to simply expand your last name with – Smith. Both Graham Cairns-Smith and John Maynard Smith were masters at this and their work continues to shape the field.

Instead of the typical three domains of life—bacteria, archaea (archaebacteria), and eukaryotes—that many now presume, Cavalier-Smith maintains that the latter two form a sister clade (neomura), whose origins refute the now popular theory that eukaryotes originated by merging an archaebacterium with an alphaproteobacterium. The defining feature of clade neomura, he suggests, is the loss of the murein wall in certain posibacteria—his world for a refined class of gram-positive bacteria. This evolution, taking place ~1.2 Gy ago, would have enabled a more flexible cell complete with novel modes of cell division, DNA segregation, phagocytosis, and ambulation.

The departure of some of Cavalier-Smith ideas from the current mainstream view takes root with the so-called “hydrogen hypothesis” which we discussed here fairly recently. When extended to its logical conclusion, this theory presumes that the above-mentioned merger that enabled the aquisition of a mitochondrial precursor (the alphaproteobacterium) by a methanogen (the archaeobacterium) precipitated the development of a complex nucleus through subsequent gene transfer from the mitochondrion, along with the prompt establishment of the other modern accoutrements of the eukaryotic cell.Via Origin of the Eukaryotic cell: Part I – How to train your endosymbiont.

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