Sea anemone is half animal, half plant

Sea anemones are classified as animals, but a surprising new research has found that these water-dwelling predatory creatures are technically half plant and half animal.
Scientists at the University of Vienna led by biologist Ulrich Technau discovered that sea anemones display a genomic landscape with a complexity of regulatory elements similar to that of fruit flies or other animal model systems.
This suggests, that this principle of gene regulation is already 600 million years old and dates back to the common ancestor of human, fly and sea anemone.
On the other hand, sea anemones are more similar to plants rather to vertebrates or insects in their regulation of gene expression by short regulatory RNAs called microRNAs.

While the genes constitute, in a sense, the words in the language of genetics, enhancer and promoters serve as the grammar.
Using sophisticated molecular approach called chromatin immunoprecipitation, Michaela Schwaiger, member of Technau's team, identified promoters and enhancers on a genome-wide level in the sea anemone and compared the data to regulatory landscapes of more complex and higher model organisms.

"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," said Schwaiger.

The Technau team was able to show that the microRNAs of the sea anemone depict all the hallmarks of plant microRNAs: They have an almost perfect complementarity to their target RNAs, which are subsequently cleaved and not inhibited like in other animals.
They also discovered a gene in the sea anemone, HYL-1, which is essential for the microRNA biogenesis in plants and was never detected in any other animal model organism before.
Moreover, when one compares the sequences of microRNAs, one microRNA with similarity to a plant microRNA as well as one microRNA with similarity to an animal microRNA can be found, researchers said.

Altogether, these findings suggest the first evolutionary link between microRNAs of plants and animals.
While the sea anemone's genome, gene repertoire and gene regulation on the DNA level is surprisingly similar to vertebrates, its post-transcriptional regulation is plant-like and probably dates back to the common ancestor of animals and plants, researchers concluded.
"This is the first qualitative difference found between Cnidaria and "higher" animals and the findings provide insight on how important levels of gene regulation can evolve independently," said researchers.
The findings are published in the journal Genome Research.