Primitive Asgard Cells Show Life on the Brink of Complexity

The finding that Lokis have actin tentacles adds plausibility to a eukaryogenesis scenario called the inside-out model, Spang and Schleper said. In 2014, the cell biologist Buzz Baum at University College London and his cousin, the evolutionary biologist David Baum of the University of Wisconsin, Madison, proposed an idea they had kicked around at family events: that the first eukaryotes were born after a simple ancestral cell extended protrusions past its cell walls. First these arms reached toward a symbiotic bacterium. Eventually they closed around that partner, turning it into a proto-mitochondrion. Both the original archaeal cell and the captured symbiote were enveloped within a skeleton provided by the arms.

Back when Asgard archaea were still known only from scraps of environmental DNA, Baum had asked attendees at a conference to draw what they thought the organisms would look like. His own drawing based on the inside-out ideas, which predicted that they would sport protruding arms, surprised the other assembled scientists. At the time, Schleper said, it seemed “so odd that he makes this funny suggestion.”

A Competitive Atmosphere

The events of eukaryogenesis have been so obscured by intervening time and gene-swapping that we may never know them with certainty.

The two Loki species currently in culture, for example, are modern-day organisms that differ from ancient archaea in the same way that a living, singing cardinal differs from the ancestral dinosaur from which it evolved. The Loki group isn’t even the subset of Asgard archaea that genetic analyses suggest is most closely related to eukaryotes. (Based on known Asgard genomes, a preprint posted by Ettema and his colleagues in March argued that the ancestor of eukaryotes was a Heimdall archaeon.)

Still, labs around the world are gambling that bringing more diverse representatives of the Asgard group into cultivation will yield a bonanza of new clues about their—and our—common ancestor. Schleper is trying. So is Ettema. So is Baum, who said his lab is soon welcoming a new colleague who will bring vials of archaea from groups like Heimdall and Odin. So is Imachi, who declined to speak to Quanta for this story.

“If I were to be interviewed by you now, I would most likely talk about new data that has not yet been published,” he explained in an email, adding that his group applauded the Schleper team’s efforts. “It is very competitive now (although I do not like this kind of competition),” he added.

Other sources also bemoaned the overly pressurized atmosphere. “It would be nice if the field would be more open to sharing,” Spang said. The pressure weighs heaviest on the young scientists who tend to take on the high-risk, high-reward cultivation projects. Success can add a glowing Nature paper to their resume. But wasting years on a failed effort can stunt their chances of ever getting a job in science. “It’s really an unfair situation,” Schleper said.

For now, though, the race continues. When the Baum cousins published their ideas about eukaryogenesis in 2014, Buzz Baum said, they assumed we’d probably never know the truth. Then suddenly the Asgards showed up, offering new glimpses of the liminal, transitional stages that boosted life from single-celled simplicity into overdrive.

“Before we destroy this beautiful planet, we should do a bit of looking, because there’s cool things on planet Earth we know nothing about. Maybe there are things that are sort of living fossils—states in between,” he said. “Maybe it’s on my shower curtain.”

Original story reprinted with permission from Quanta Magazine, an editorially independent publication of the Simons Foundation whose mission is to enhance public understanding of science by covering research developments and trends in mathematics and the physical and life sciences.

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