Evolution in action: the sea lily - half plant, half animal

The Israeli researcher Yehu Moran also participated in the research, who in the meantime has returned to Israel - to his own laboratory at the Hebrew University. Because the sea lily shows similarities in the genetic control elements to the fruit fly and other model animals, while the transcription after the control is the same as in plants, this principle of complex gene control already existed in the common ancestor of humans. , fruit flies and sea anemones 600 million years ago, the researchers say

Another proof of the interesting ways of research in the field of evolution to decipher the tree of life close to its root - the split between the kingdoms of plants and animals. A team of researchers led by the evolutionary and developmental biologist Ulrich Technau (Ulrich Technau) from the University of Vienna discovered that the sea anemone, which exhibits the outward activity of a plant, exhibits a genomic configuration and a complexity of control factors similar to those of the fruit fly and other animals. This means that the principle of gene control is already 600 million years old and dates back to the ancestor of humans, flies and sea lilies. However, sea anemones are more similar to plants than to vertebrates or insects in terms of controlling gene expression through microRNA.

This surprising evolutionary finding was published in two papers in the journal Genome Research. The main researcher of the article that dealt with microRNA, Yehu Moran, worked in Technau's laboratory at the University of Vienna as part of post-doctoral research and is currently a senior lecturer in the Department of Ecology, Evolution and Behavior at the Hebrew University. Moran heads a group of researchers that continues to investigate the phenomenon.

Our external appearance and the way our body works, in addition to environmental influence, are the result of the action of our genes. However, genes are rarely single players; They act like musicians in a concert and criticize each other's activity and expression in a network of genetic control.

A simple creature with a complex gene content

In the last decade, the sequencing of the human genome and that of many animals has shown that anatomically simple creatures such as sea anemones contain a genetic repertoire similar to that of more developed animals. This means that the difference in morphological complexity cannot be easily explained by the presence or absence of this or that gene. Some researchers speculate that it is not the individual genetic code that is responsible for complex body programs, but the way in which genetic codes are networked and connected with each other. Accordingly, the researchers expect the gene network to be less complex in simple creatures than in humans or other higher animals.

A measure of the complexity of gene control can be the distribution and density of control sequences in genes. These motifs in DNA are called "amplifiers" or "promoters", and they can bind together transcription factors in a special way and usually control the expression of the target genes in unique spatial and temporal patterns. "Discovering these short motifs in oceans of nucleotides is not a natural thing" explains Technau, a professor in the Department of Molecular and Developmental Evolution at the University of Vienna.

While the genes constitute, in a sense, the words in the genetic language, the enhancers and promoters serve as its grammar. These control elements are associated with biochemical epigenetic adjustments of the histones, proteins that are interwoven with DNA and make up the chromatin.
Using a sophisticated molecular approach known as chromatin immunoprecipitation, the researchers in Technau's laboratory were able to identify enhancers and promoters throughout the sea anemone genome, and compared the data to the control elements of more complex animals used as model animals.

"Since the sea lily shows similarities in the genetic control elements to the fruit fly and other model animals, we believe that this principle of complex gene control already existed in the common ancestor of humans, fruit flies and sea lilies 600 million years ago," says Michaela Schweiger from the Techno team.

Ultimately, gene expression led to the creation of the proteins, the factors that affect the functioning of our bodies. In addition to controlling the transcription of DNA into RNA, gene expression can also exert post-transcriptional control when the RNA has already been formed. Here the microRNA plays an important role. microRNAs are pieces of RNA used for control and their ability to attach to the target RNA, suppress its translation or lead to its disconnection. In recent years hundreds of microRNA fragments have been identified in many animals and over a thousand of them in humans. Many of them have an important role in metabolism and are essential for the development process. Mutations in certain microRNAs have been found to be associated with diseases, including many types of cancer. Each microRNA can attach to different RNA segments with specific binding. "We estimate that 30-50% of all human genes are controlled by microRNAs" says Technau. "However, the evolutionary origin of microRNAs in animals is still unclear."

In an interview with the Hidan site, Dr. Moran says: "Michaela's article shows the aspects of transcriptional control shared between sea anemones and other animals such as insects and vertebrates, while my article shows a control system based on microRNA that is shared between sea anemones and plants and is very different from the control system of the microRNA in other animals, which indicates that the system we find in sea anemones is probably very ancient and already existed in the common ancestor with plants."

"MicroRNAs have also been discovered in plants, but it is believed that they appeared independently of human microRNAs. This assessment is based on the fact that they do not show similarity in sequence, they have different biogenesis pathways, and they also show different patterns of action: plant microRNAs only bind to a small number of targets and are very sequence specific, unlike those of animals. In collaboration with researchers from the USA, Norway and France, the researchers isolated 87 microRNAs from the sea anemone."

"We were able to show that microRNAs from the sea anemone display all the typical characteristics of plant microRNAs: they match almost perfectly to their target RNA and they lead to the degradation of the target RNA and not to its inhibition as in other animals. The researchers also discovered the existence of the HYL-1 gene in the sea lily, which is essential for biogenesis in plants and has never been discovered in another animal. Moreover, when the researchers compared the sequence of the microRNAs, they found that for every microRNA similar to plants there was at least one that resembled animal microRNAs. This finding shows for the first time the evolutionary relationship between plant and animal microRNAs."

In conclusion, while the sea anemone genome, the genetic repertoire and gene control at the DNA level, are surprisingly similar to those of vertebrates, the post-transcriptional control is similar to that occurring in plants and may be the legacy of the last common ancestor of animals and plants. This is the first qualitative difference found between Cnidaria and higher animals. These findings provide insight into the way in which important levels of genetic control can evolve independently during evolution.

For information on the website of the University of Vienna