Although scientists generally agree that eukaryotes can trace their ancestry to a merger between archaea and bacteria, there’s been considerable disagreement about what the first eukaryote and its immediate ancestors must have looked like. As Thattai and his colleagues Buzz Baum and Gautam Dey of University College London explain in their paper, that uncertainty has stemmed in large part from the lack of known intermediates that bridge the gap in size and complexity between prokaryotic precursors and eukaryotes. As a result, they say, the origin of the first eukaryotic cell has remained “one of the most enduring mysteries in modern biology.”
That began to change last year with the discovery of DNA sequences for an organism that no one has ever actually seen living near a deep-sea vent on the ocean floor. The genome of the archaeon known as Lokiarchaeum (‘Loki’ for short) contains more “eukaryotic signature proteins” (ESPs) than any other prokaryote. Importantly, among those ESPs are proteins (small Ras/Arf-type GTPases) critical for eukaryotes’ ability to direct traffic amongst all those intercellular compartments.
The authors consider the available data to explore an essential question: what might the archaeal ancestor of all eukaryotes look like? “If we could turn back the clock and peer inside this cell, would its cellular organization have been like that of an archaeal cell or more eukaryote-like?” Dey says.
As the closest known archaeal relative of eukaryotes, Loki helps to answer that question. The researchers say that the ESPs found in Loki are unlikely to work in the same way they do in eukarytoes. That’s because Loki doesn’t appear to have enzymes required for ESP association with membranes or key building blocks of the membrane trafficking machinery. Paper. (public access) – Dey et al. On the archaeal origins of eukaryotes. Trends in Cell Biology, 2016 DOI: 10.1016/j.tcb.2016.03.009 More.
Let’s test drive this theory in a real life situation with no intelligent intervention at all. See what happens.
See also: Magnetism enabled multicellular life
Maybe if we throw enough models at the origin of life… some of them will stick?
With Enceladus the toast of the solar system, here’s a wrap-up of the origin-of-life problem
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