evolution: the role of Asgard Archaea (Introduction)

by David Turell , Saturday, March 22, 2025, 21:04 (13 days ago) @ David Turell

A gateway to eukaryotes:

https://phys.org/news/2025-03-life-special-group-celled-laid.html

"Asgard archaea appeared almost heaven-sent for research: They turned out to be a missing link between archaea and eukaryotes—that is, between archaea and organisms whose cells contain a nucleus, such as plants and animals.

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"In that study, Pilhofer and his postdoctoral researchers Jingwei Xu and Florian Wollweber demonstrated that Lokiarchaeum ossiferum possesses certain structures also typical of eukaryotes. "We found an actin protein in that species that appears very similar to the protein found in eukaryotes—and occurs in almost all Asgard archaea discovered to date," says Pilhofer.

"In the first study, the researchers combined different microscopy techniques to demonstrate that this protein—called Lokiactin—forms filamentous structures, especially in the microbes' numerous tentacle-like protrusions. "They appear to form the skeleton for the complex cell architecture of Asgard archaea," adds Florian Wollweber.

"In addition to actin filaments, eukaryotes also possess microtubules. These tube-shaped structures are the second key component of the cytoskeleton and are comprised of numerous tubulin proteins. These tiny tubes are important for transport processes within a cell and the segregation of chromosomes during cell division

"The origin of these microtubules has been unclear—until now. In a newly published article in the journal Cell, the ETH researchers discovered related structures in Asgard archaea and describe their structure. These experiments show that Asgard tubulins form very similar microtubules, albeit smaller than those in their eukaryotic relatives.

"However, only a few Lokiarchaeum cells form these microtubules. And, unlike actin, these tubulin proteins only appear in very few species of Asgard archaea.

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"Was the cytoskeleton essential for the development of complex life? While some questions remain unanswered, the researchers are confident that the cytoskeleton was an important step in the evolution of eukaryotes.

"This step could have occurred eons ago, when an Asgard archaeon entwined a bacterium with its appendages. In the course of evolution, this bacterium developed into a mitochondrion, which serves as the powerhouse of modern cells. Over time, the nucleus and other compartments evolved—and the eukaryotic cell was born.

"'This remarkable cytoskeleton was probably at the beginning of this development. It could have enabled Asgard archaea to form appendages, thereby allowing them to interact with, and then seize and engulf a bacterium," says Pilhofer."

Comment: it appears these are our direct ancestors as we must have came from bacteria which represent first life.