Sea Anemone Is Both Animal and Plant

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Sea anemones are classified as being animals, but two new genetic studies have found that these water-dwelling creatures are technically half plant and half animal.

The discovery does not change the classification of sea anemones, but the studies -- both published in the latest issue of the journal Genome Research -- reveal just how interconnected life on Earth is.

"All animals living now, including humans, are equally distant (i.e. distantly related) to plants," project leader Ulrich Technau told Discovery News. "However, the sea anemones are representatives of an animal lineage called the cnidarians (corals, sea anemones, jellyfish and hydras), which branched off very early and appear to have retained many ancestral traits."

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Technau, an evolutionary and developmental biologist at the University of Vienna, and his teams determined that, remarkably, cnidarians use a plant-like system to control animal genes.

For the studies, the researchers focused on gene expression, which is the process by which information from a gene is used in the synthesis of a functional gene product, such as proteins or large biological molecules known as RNA.

Gene expression involves at least two main steps: transcription and translation. Transcription is the process of making an RNA copy of a gene sequence. Translation is the process of translating the sequence of a messenger RNA molecule to a sequence of amino acids during protein synthesis.

The scientists determined that regulation of transcription for sea anemones is comparable to that for other animals. On the other hand, the second level of regulation for sea anemones, translation, is much more plant-like.

"Since sea anemones have branched off very early, we assume that they have retained this plant-like mode from a common ancestor, hence, in terms of the regulation of gene expression, they are somewhat mixed," Technau said.

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The basic animal aspects of gene expression, which we share with them, evolved a very long time ago.

Co-author Michaela Schwaiger explained, "Since the sea anemone shows a complex landscape of gene regulatory elements similar to the fruit fly or other model animals, we believe that this principle of complex gene regulation was already present in the common ancestor of human, fly and sea anemone some 600 million years ago."

While sea anemones branched off, still retaining some of their plant-like ways, the common ancestor of insects and vertebrates (including mammals, birds, reptiles, amphibians and fishes) either lost these genetic ways of plants, or drastically modified them.

Technau suspects that the common ancestor of sea anemones, humans and flies was "a simple-looking pear or worm-shaped" creature with a basic nervous system, an oral opening and a gut.

David Miller of James Cook University's Coral Genomics Group described the papers as "very elegant and thorough."

"Cnidarians appear to use a plant-like system to regulate typical animal genes, many of which are shared between the sea anemone and you and me. How cool is that?" Miller said.

As Technau concluded, "Maybe it is worth trying to learn something from organisms that have managed to survive over 600 million years."

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