Simple sea anemones are not so simple after all

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This Pachycerianthus magnus The tubular anemone has a surprisingly complex mitochondrial genome, researchers from the state of Ohio discovered. Credit: Sergio Stampar.

The tubular anemone is an ancient sea creature that looks like a prehistoric flower. Animals lead slow, long and predictable lifestyles and are very similar from one species to another.

It would be easy to use the word "simple" when considering that parent of coral and jellyfish. But wait, not so fast.

New research on tube anemones is challenging everything evolutionary biologists thought they knew about the genetics of marine animals. The mitochondrial DNA of the tubular anemone, or Ceriantharia, is a true scratcher of the head, that it 's an unexpected or a magnitude previously unimaginable.

Researchers, including a team from Ohio State University, have released new findings showing that anemone tube DNA does what few mitochondrial genomes of other species have shown. It defies the classic form of the donut in which it "should" be and is organized in several fragmented pieces, the number of which varies according to the species.

On top of that, the animal now holds the record for the largest mitochondrial genome reported to date. It contains nearly 81,000 base pairs, or genetic information, according to the new study published online in the newspaper Scientific reports. Human mitochondrial DNA contains less than 17,000 base pairs.

"These ancient animals have simple behavior and simple anatomy, which is why we have considered them as fairly simple creatures up to now, but their biology is quite complex.The genomes of these tube anemones can to be more dynamic than those of more complex and complex animals, newer animals like snails, insects and vertebrates, "said Meg Daly, professor of evolution, ecology and biology of organizations at Ohio State.

About mitochondrial DNA that is at the heart of this study: This is not the DNA that most of us remember having learned at the time. school – the instructions found in the core of each cell of an organism and organized in linear double helix.

On the contrary, mitochondrial DNA usually has a circular shape and contains much less information than nuclear DNA. And he lives inside mitochondria – double-membrane structures found in multitudes inside the cell, outside the nucleus. Mitochondria are responsible for the production of energy and are sometimes called the "cellular powerhouses" of living things.

Scientists have been able to sequence mitochondrial DNA from other similar animals, but until now, they have hit an obstacle with these tubular anemones, Daly said. About two decades ago, a researcher attempted to create a mitochondrial genome plan based on the theory that it would be circular.

"It was impossible and nobody really knew why, until now," said Daly, who has led a career studying sea anemones and their biodiversity.

This Isarachnanthus nocturnus The tubular anemone has the largest animal mitochondrial genome reported to date, according to a team of researchers, including a group from Ohio State University. Credit: Sergio Stampar

Using advanced computer technology, the researchers examined two species of tubular anemones and found that one of them had five linear fragments of mitochondrial DNA and the other had eight. Previously, scientists had discovered a linear genome in jellyfish mitochondria, but the linear structure combined with the variation in size and number of fragments seen in the tubular anemone is unprecedented.

"We think that the typical arrangement of the loops we find is logical, because one of the advantages of circular-genome mitochondria is that it replicates itself easily," she said.

"We thought of this loop-shaped design to help mitochondria do their job quickly and efficiently."

Daly and the others who study these creatures must now understand why this could have happened from the point of view of evolution.

"Until now, there is no rhyme or reason for anemones to have this unusual mitochondrial genome," Daly said.

Sergio Stampar, the Brazilian researcher who led the study, said that the two species examined in this study represented the most important groups of Ceriantharia.

"These results present a considerable" photograph "of the group.In addition to the large size of the genomes, the most surprising thing that we have found is the significant difference between the two species," said Stampar, who works at the Universidade Estadual Paulista of São Paulo. .

Stampar said the work raises many questions because the presumed change of circular genomes to linear genomes in anemones should not be a simple process. An extensive discussion on the evolution of several groups of related animals called Cnidaria – including jellyfish, corals and sea anemones – is imperative, he said.

It would be tempting to expect similarities in the evolving pressures among marine animals that are all old and relatively simple in terms of appearance and function, but this new evidence calls into question this, said Daly. .

"Maybe they all started at the same place, but were subjected to different patterns and opportunities for change."