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This tiny marine organism holds the key to the origin of neurons

The Placozoans They are small sea creatures that cling to surfaces. So insignificant that they were discovered by the German zoologist Franz Eilhard Schulze in 1883 on the walls of a marine aquarium. For decades, their existence eluded biologists until they were recognized in the 1970s as one of the five major animal lineages. Centophora (medusa), Porifera (sponges), Cnidaria (corals, sea anemones and jellyfish) and Bilateria (all other animals) – and are thought to have first appeared on Earth about 800 million years ago.

Now, a team of researchers at the Center for Genome Regulation in Barcelona (CRG) studied these organisms in detail and found that they contain some of the basic components of a neuron, but long before these basic units of the nervous system appeared in evolution. The result which is published on Tuesday in the magazine cellIt leads them to interpret that some key components of the nervous system evolved in the first ancestral animals, providing new clues about how they came to be.

“evolutionary springboard”

“We have known for a long time that these organisms have a key phylogenetic position in the history of animals, and that is why we began to study them,” explains the co-author of the study. Xavier Grau-Bovetill “What we see is that even though they don’t have neurons, at the molecular level they are similar to neurons in other animals. That is, at least half of the elements necessary for the synapse are already regulated in the ancestor, and the other half appeared later.”

The researchers observed that, although they do not have a nervous system, placozoans coordinate their behavior thanks to “peptidergic” cells, since they release small peptides and can control the animal’s movement or feeding. To study the origins of these cells, they used a series of molecular techniques and computational models to understand how placozoan cell types evolved and reconstruct how our ancient ancestors existed and functioned.

To their surprise, the cells that released the peptides had many similarities to neurons, a cell type that appeared many millions of years later in more advanced animals such as Bilateria. Species analysis showed that this similarity is unique to placozoans and is not seen in other early branching animals such as sponges or comb jellies (ctenophores).

This allows us to answer such interesting questions as whether the nervous system was invented multiple times or piecemeal.

Xavier Grau
Researcher at the Barcelona Center for Regulation of the Genome (CRG)

“We were surprised by the parallels,” adds the first co-author of the article. Sebastian R. Najle. “Peptidergic cells in Placozoa have a lot in common with primitive neuronal cells, even if we’re not there yet.” “It’s like watching an evolutionary trampoline.” “We’re looking at an essential part of what constitutes a neuron in modern organisms, and this allows us to see at what point in evolution it arose,” says Grau. “This allows us to answer interesting questions such as whether the nervous system was invented multiple times or piecemeal.”

Complete the puzzle

“The discovery of ancestral genes from current cells (neurons or any other) is not surprising,” says the neuroscientist and popularizer. Xurxo Mariño. “I think it’s interesting, in addition to dating these central genes, that the battery of genes they discover will better define the evolutionary puzzle between ctenophores, cnidarians, placozoans, and bilaterians (us and many others).”

In the absence of studying the details, the professor of medicine Luis Pueles believes that the findings of this new study are exciting and provide “significant evolutionary precision within what was previously assumed in the field, that single neurons are of very ancient origin in invertebrates.” In any case, remember, “Although the peptidergic neuron family is important, there are other types of putative non-peptidergic neurons (although it is never known whether any neurons can release peptides that have yet to be discovered).

Salvador MartinezA professor and researcher at the UMH-CSIC Institute of Neuroscience, he also believes that this is a very well-argued article methodologically and conceptually. “It can help us understand the process by which a group of cells in multicellular organisms that is regulated by paracrine phenomena is linked by the selective connectivity properties of the progenitors of the nervous system,” he notes. “A relevant aspect for understanding how the functional properties of neurons arose in the cells of simple organisms.”

“Dawning” of a neuron.

The authors emphasize that peptidergic cells are far from a true neuron because they lack components necessary to receive neuronal messages (postsynaptic) or to conduct electrical signals. The result indicates that these cells communicated using neuropeptides, but over time they acquired new genetic modules that allowed them to form postsynaptic structures, form axons and dendrites, and create ion channels that generate fast electrical signals: innovations that were fundamental to the emergence of neurons. About a hundred million years ago, after the ancestors of placozoans first appeared on Earth.

In a metaphorical sense, if these results are confirmed, we may be witnessing the dawning of neuron components in the shallow seas of the old Earth and, in a very distant and indirect way, the steps that led to our appearance. The brain (the first modern neuron is thought to have arisen in the common ancestor of cnidarians and bilaterians about 650 million years ago. Of course, we still need to know the evolutionary history of nervous systems in detail and study other groups of animals in depth to compare their gene expression. “It’s not It’s like we’ve found the great grandfather of neurons, but it’s like we’ve found a key and a loose part in these creatures,” Grau says. “The first major part of the nervous system and the first step in its evolution.”

Source: El Diario





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