Sea anemone is both plant and animal

Researchers find genetic characteristics of plants in the cnidarian

Adult polyp of the sea anemone Nematostella vectensis. © Nature
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Plant or animal? The sea anemone looks like a plant, yet it belongs to the nettle "animals". Scientists from Austria have found in genetic studies that sea anemone is far from being such a simple organism as previously thought: in two publications in the journal "Genome Research", they explain why the sea anemone is similar to both animals and plants.

Since the 1990s, complete gene sequences have been known by an increasing number of organisms. Using these genomes, scientists can determine with increasing accuracy the relationships of individual species, as well as entire strains of living things. Among other things, it was shown that the size of the genome does not necessarily indicate how complex an organism is. An equally important role is played by the interaction of genes with each other and their regulation. Ulrich Technau from the University of Vienna and his colleagues have now deciphered this gene regulatory network at the sea anemone - and found some surprising results.

Complex gene regulation in a simple organism

For their "gene map", the researchers identified certain elements in the DNA sequence, called "enhancers" and "promoters". These elements dock with specific proteins, which in turn influence how often and how strongly a gene is activated and copied. The more complex the regulatory network of a living being, the more frequently these enhancers and promoters occur in the genome.

In the case of the sea anemone, it turned out that the rather primitive animal has a similarly complex network as the human or the fruit fly. "We therefore conclude that this principle of complex gene regulation goes back to common ancestors of humans, fly and sea anemone, " explains microbiologist Michaela Schwaiger. The common system of gene regulation would therefore be at least 600 million years old.

Common ancestor also with plants?

The sea anemone, however, proves to be surprising in another respect as well. Because even in another system of gene regulation, unexpected peculiarities were revealed. In this case, so-called microRNAs bind to the RNA copies of an activated gene. This way, they prevent the gene from being translated into a functioning protein. This second system is very common, in many animals 100 to 200 such micro-RNAs are known, in humans even more than 1, 000. Even in plants, this type of regulation exists, but scientists assume that it has developed completely independently: The plant micro-RNAs have almost nothing in common with the animal, they arise in other ways and act differently. display

In the sea anemone, the team found a total of 87 of these microRNAs. Surprisingly, they showed all the properties of plant microRNA. In addition, the researchers identified an important protein for the production of microRNA, which was previously found only in plants. This suggests that these peculiarities of the sea anemone go far back to the common ancestor of animals and plants.

On the one hand, the gene regulation in the sea anemone at the DNA level is remarkably similar to the system of the "higher" animals. On the other hand, it resembles plants in RNA regulation. The scientists see this as a significant demonstration of how important levels of gene regulation can develop differently.

(Genome Research, 2014; doi: 10.1101 / gr.162529.113, 10.1101 / gr.162503.113

(University of Vienna, 19.03.2014 - AKR)