Half plant, half animal: The surprising genetics of the sea anemone

Out of all the characters under DC Comics's stable, few are as unique or eye-catching as the Swamp Thing: a powerful yet tragic combination of a human's consciousness trapped inside a mystical, vegetable-like body, the character exists as both a plant and an animal, cursed to live out the rest of his days in his nightmarish, green-tinted form.

If the concept of an organism with both plant and animal qualities seems too outrageous for you, think again – the sea anemone begs to differ.
 

A team of scientists led by the University of Vienna’s Ulrich Technau has determined that the sea anemone has an interesting genetic makeup; while the complexity of the underwater creature's regulatory elements is similar to animals (particularly to fruit flies), the way they regulate their genes is closer to that of plants.

'Planted' evidence

More often than not, genes function in conjunction under a system of gene regulatory networks. They regulate each other's activity and expression (the process in which the information from a gene is used to generate a functional gene product, often proteins) and hardly ever function independently.
During gene expression, single-strand RNA is transcribed, binding specific genes to the DNA template. This is where the regulatory sequences of DNA, known as enhancers and promoters, facilitate the expression of target genes by binding to transcription factors (the regulatory proteins that stimulate DNA transcription).

Through the use of a sophisticated molecular approach called chromatin immunoprecipitation, the researchers were able to identify promoters and enhancers in the sea anemone's genomes, and determined that the creature's gene regulation is surprisingly as complex as higher-model organisms.

"Finding these short motifs in the ocean of nucleotides is far from trivial," said Technau, a professor at the University’s Department for Molecular Evolution and Development.

Rooted in a 600 million-year old mystery

However, the process of gene expression isn't limited to just the transcription of DNA to RNA; expression can also be regulated post-transcription. MicroRNAs are short, regulatory RNA strands that bind to target RNAs and serve as inhibitors that affect metabolism, and developmental processes. Mutated microRNAs are also associated with serious diseases such as cancer; a study even points to microRNA as a factor in the development of schizophrenia.

Amazingly, after isolating 87 microRNAs from the sea anemone sample, the scientists discovered that the organism's microRNAs appear to be very similar to those of plants'. Aside from the fact that they have “an almost perfect complementarity” to their RNA targets (cleaved and not inhibited as in other animals), the sea anemone also possessed the gene HYL-1, an essential component of the microRNA biogenesis in plants that has been notably absent in other animal model organisms examined in the past.

These findings point to the first evolutionary link between microRNAs of plants and animals.

"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,” explained study co-author Michaela Schwaiger.

The researchers’ findings were published as two separate papers in the science journal Genome Research. — TJD, GMA News