An archy sheds light on the evolutionary history of the eukaryotes, this group of the lifetime to which we belong, like all the other multicellular.
by Eva Desvigne-Hansch
The first stages of the evolution of the living have not finished intriguing scientists. However, the discovery of a new archée of Archée allowed researchers to take one more step towards understanding the origin of the eukaryotes, this vast branch of the living to which we belong.
We traditionally divide the living tree into three main branches: true ebacteria or bacteria; Archaea, another group of unicellular microorganisms; And the eukaryotes. The latter group, even if it is not the largest, remains the most studied, because it is the only one to have seen the emergence of multicellulitularity. The eukaryotes, that is to say both humans and planktonic algae or fungi, are distinguished by a complex cell architecture.
a debated origin
The fundamental characteristic of eukaryotic cells is the presence of a nucleus, a pocket delimited by a double membrane containing the genetic material. But they also have other organelles (structures specializing in a given cellular function) such as mitochondria (energy factories of cells) and an internal membrane network called endoplasmic reticulum. Finally, they have a cytoskeleton of actin, a network of long filamentous proteins that structure and give their shapes in the manner of microscopic cables.
However, the origin of the eukaryotes remains debated. Recent phylogenetic data, the study of kinship links between species during evolution, suggest that this group would have emerged from a line of archaea called “Asgards”. Indeed, we find in the genome of the Asgards hundreds of genes that we thought specific to eukaryotes. To explain this astonishing kinship, Japanese researchers had proposed in 2020 a hypothetical model according to which the eukaryotes would come from an ASGARD having issued long membrane protrusions (extensions of the cell) which by merging would, on the one hand, formed the Different internal membrane compartments and, on the other hand, encompasses a ebacterious ebacterium at the origin of current mitochondria.
Until then, however, scientists were unable to validate this model, struggling to isolate and therefore observing these potential cousins. It is now done: Researchers from Vienna and Zurich have managed to cultivate in laboratory a strain of Asgard from Slovenian sediments. By observing these unices with an electron microscope, the researchers noticed that the ASGARDS actually emitted long, burgeoning membrane protrusions. Even more interestingly, they showed that these protrusions were structured by actin filaments, similar to what could be observed in a eukaryote. This complex cellular architecture, unprecedented in a non-Eucaryote, goes well in the direction of the model proposed by Japanese researchers.
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