Placozoo: A strange pancake-shaped animal creature shows the origin of thought | Science | EUROtoday

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Movement of a placozoan observed with a microscope.
Movement of a placozoan noticed with a microscope.CRG

A multitude of religions from throughout the planet agree on the identical story of the creation of the human being, by which an omnipotent god creates men and women from nothing with a mind already effectively furnished. The actuality is way much less lyrical, as prompt by placozoans, animal creatures smaller than a millimeter that float in seawater like grains of sand. They go unnoticed, however they’re extraordinary. Under the microscope, they’re like tiny pancakes, with none organs, a lot much less a mind. However, these strange animals are succesful of coordinating to assault their prey as a gaggle. The workforce of Spanish biologist Arnau Sebé Pedrós revealed this Tuesday that in the cells of these uncommon beings the origin of the neurons, liable for human thought, can already be sensed.

Placozoans have simply 50,000 cells, however their skills are stunning. They are immortal, as a result of they’ll multiply indefinitely asexually. A piece of placozoan will kind one other placozoan. They may also be reconfigured and take different shapes apart from a pancake, corresponding to a donut or a whip. A individual is made up of 30 trillion cells, with a mess of well-differentiated varieties, corresponding to neurons in the mind or pink blood cells. Placozoans, on the different hand, are two easy layers of related cells, caught collectively like two slices of cheese. Its simplicity may also help us perceive how single-cell organisms got here collectively and created more and more subtle multicellular beings.

A placozoan noticed beneath a microscope.Bernd Schierwater

Arnau Sebé Pedrós’ group cares for hundreds of placozoans of their laboratory at the Center for Genomic Regulation, in Barcelona. According to his calculations, multicellular animals emerged about 850 million years in the past. Very quickly, 800 million in the past, the paths of the households that gave rise to placozoans and people diverged. “People have a tendency to see living fossils in nature. We don’t know if our common ancestor looked like a placozoan, but some aspects of its biology were already there,” says the biologist, born in the Lleida town of La Fuliola 37 years ago.

The team has studied the four known species of placozoans cell by cell, including the first one discovered, found in 1883 by the German zoologist Franz Eilhard Schulze in a marine fish aquarium in Graz (Austria). Schulze baptized that mysterious creature with the scientific name Adherent trichoplaxfrom Greek tricho (hair and plax (plate) and from Latin clinging (sticky): sticky hairy plate, due to its tendency to land on algae to devour them. They are the simplest animals on the planet, except for myxozoans, parasites with few cells that cannot live on their own.

The Argentine researcher Sebastián Najle, co-author of the work, manages placozoans at the Center for Genomic Regulation, in Barcelona.
The Argentine researcher Sebastián Najle, co-author of the work, manages placozoans at the Center for Genomic Regulation, in Barcelona.Omar Jamshed / CRG

Sebé Pedrós and his colleagues have observed that placozoans are capable of coordinating their 50,000 cells thanks to the fact that some of them can send messages to each other using molecules called neuropeptides, like the neurons in our brain do. “We have found a rudiment of certain aspects of our nervous system,” celebrates the biologist. These secretory cells nonetheless lack the processes that transmit nerve impulses (axons) and the processes that obtain them (dendrites) in human neurons.

The new results, published this Tuesday in the specialized magazine Cell, support the chemical brain hypothesis, postulated by the Hungarian biologist GásPAR Jékely, from the University of Heidelberg, in Germany. “This study reveals profound molecular similarities between neurons of placozoans and neurons of bilateral animals.” [los simétricos, como los seres humanos]”says Jékely. “These similarities, along with the indisputable fact that placozoan neurons solely talk by way of chemical alerts, help the concept that nervous programs might have first developed as a set of various, chemically linked cells, earlier than creating specialised processes (axons and dendrites) and synapses,” says the Hungarian researcher, who has not participated on this examine.

Sebé Pedrós emphasizes this concept. “Probably, to coordinate the cells of a small organism, with only two layers, it was enough to have cells secreting chemical signals. However, the moment you get big and start to gain three-dimensionality, you also need to emit electrical signals and have cell-to-cell communication interfaces, which are synapses,” explains the Spanish biologist. The neurons of a tall individual, with extensions that permit a stimulus to be instantly felt in the foot, can measure greater than two meters.

Image of a placozoan, obtained with a confocal microscope.
Image of a placozoan, obtained with a confocal microscope.CRG

Arnau Sebé Pedrós’ group believes that the first fashionable neuron didn’t seem till about 650 million years in the past, in the widespread ancestor of the group of jellyfish—the cnidarians—and that of human beings. The nice thriller is what occurred then to a different department of animals that set out by itself path 850 million years in the past: the ctenophores, organisms much like jellyfish and that even have neurons, though completely different. “It is still too early to say that ctenophores invented neurons independently, but I think there is more and more evidence that this could be the case,” explains Sebé Pedrós.

German Bernd Schierwater has been finding out placozoans for many years. On his web site for the Hannover Veterinary Faculty he seems in the sea with a tie and sun shades, in the shallow waters by which these animals often seem. In his opinion, the new examine, by which he has collaborated, confirms his “new placula hypothesis”, in line with which the hypothetical final widespread ancestor of all animals was a two-layered disk, like the placozoans. “The original hypothesis comes from a German zoologist, Otto Bütschli, more than a century ago. Later, for political reasons and for fame and money, trees of life were published that placed the ctenophores at the base. This is absolute rubbish, but the researchers put money in their pockets,” says Schierwater.

American scientist Carolyn Smith has additionally investigated placozoans, at the National Institute of Neurological Disorders and Stroke, in Bethesda (USA). Smith declares herself “excited” about the outcomes of the Barcelona workforce. “It is strong support for the idea that the evolutionary precursor of neurons could have resembled the peptidergic secretory cells found in placozoans,” she celebrates.

Arnau Sebé Pedrós team (in the center, seated, with a gray shirt), at the Center for Genomic Regulation, in Barcelona.
Arnau Sebé Pedrós workforce (in the heart, seated, with a grey shirt), at the Center for Genomic Regulation, in Barcelona.CRG

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