Biologists from Russia and foreign countries have discovered an extremely unusual unicellular organism that made them doubt the generally accepted ideas about the evolution of the most primitive ancestors of humans and other multicellular animals.
“Ancoracysta twista is a separate and unknown evolutionary line of the tree of life of the kingdom level.This organism has a unique structure and form.We have shown that mitochondrial genes have been lost many times in different groups of eukaryotes during their evolution as opposed to a single large-scale loss of genes in the general ancestor of all organisms with a separate nucleus, “says Denis Tikhonenkov from the Institute of Biology of Inland Waters of the Russian Academy of Sciences, whose words are quoted by the press service of the Russian Science Foundation.
According to modern concepts, eukaryotes – complex cells with a separate nucleus and a complete set of other organelles – appeared as a result of “assimilation” of their ancestors of various bacteria and archaea. A typical example of this process are mitochondria – cellular “energy stations” that synthesize the basic “energy currency” of cells – adenosine triphosphate molecules.
They are separated from the rest of the cell by a double membrane, similar to the bacterial membrane, and also have their own DNA and a protein synthesis system. The organs of photosynthesis of plants and algae – chloroplasts – have a similar nature. The “taming” of mitochondria, as biologists now believe, was a key step in the evolution of our unicellular ancestors.
Since mitochondria play a critical role in the life of cells and humans, as well as all other eukaryotes, many scientists today believe that this “domestication” was completed at the very first stages of the evolution of multicellular living beings – even before the ancestors of protozoa, animals, fungi and plants.
Tikhonenkov and his colleagues from Europe and America found out that this was probably not the case, having discovered an unusual single-celled creature, Ancoracysta twista, found on the surface of one of the corals in the tropical seas of the Earth, whose mitochondria are not similar to the similar parts of the cells of all the rest eukaryotes.
The study and comparison of the structure of approximately two hundred proteins, which are critical for the work of cells and therefore little changed during evolution, has shown that this creature does not have close relatives among all modern eukaryotes. Moreover, it turned out that its mitochondrial genome was “incorrectly” arranged for such a primitive being, very close to the common ancestor of all organisms with an isolated nucleus.
“Hunting harpoon” Ancoracysta twista, the most unusual and “alien” creature on earth
For example, it contained an “extra copy” of the instructions for assembling the cytochrome protein that was simultaneously present in the nuclear DNA of the very single-celled creature, as well as an almost complete set of genes associated with ribosome work that were lost by the mitochondria at the initial stages of their fusion with human ancestors and other animals.
As scientists explain, earlier evolutionists believed that most of the genes that control the development of mitochondria “moved” into the DNA of future eukaryotic cells during a single process of transferring genetic material. An example of Ancoracysta twista shows that this happened not at once, in two stages or more, and that his last steps could proceed according to completely different scenarios from the forerunners of different kingdoms of multicellular creatures.
According to Tikhonenkov, other seas with the same unusual “genealogy” may disappear in the seas and other corners of the Earth, the study of which will help scientists understand how the first multicellular creatures of the Earth and their simplest relatives actually appeared.