On the left is the reconstruction of the brain of Platynereis, which was assembled from microscope images of 36 individual individuals, and on the right the mapping of active genes on this brain representation. The view corresponds to the brain of a 48-hour-old larva of the marine ringworm. Credit: EMBL / R.Tomer
Readings Simple invertebrates such as the marine ringworm have nerve structures that resemble the cerebrum, as it occurs in humans. This is what a research team led by Detlev Arendt from the European Molecular Biology Laboratory (EBML) in Heidelberg has discovered for the first time using a novel analytical method. The results allow conclusions to be drawn about the developmental history of the brain, for example what the oldest highly developed brain regions might have looked like and what their tasks were. How the cerebellum of the vertebrates evolved from the invertebrate ancestors in the course of evolution has so far been largely unclear. Thus, even in the next invertebrate relatives of the vertebrates, the lancelet, no brain structure similar to the cerebrum could be detected. However, the research team led by Detlev Arendt in the marine ringworm Platynereis dumerilii has for the first time discovered brain structures that are similar to the vertebrate cerebrum. Platynereis dumerilii is a distant relative of the earthworm and lives in coastal waters of the tropics and temperate latitudes. He is in the pedigree of animals much further away from the vertebrates than the lancet fish: The developmental pathways of ringworm and humans separated already about 600 million years ago, the scientists emphasize.

In their study, they analyzed a particular brain region of the marine ringworm, which is responsible for the processing of odor and other sensory stimuli: the so-called mushroom body. Using a newly developed technique, Arendt and his team first succeeded in analyzing the molecular structure of this brain structure. "The comparison of molecular fingerprints to the developing fungus body in the worm with the available data from vertebrates was unambiguous, " says Arendt. "Mushroom bodies and cerebrum must have had a common precursor in evolutionary history." This primal structure presumably consisted of a collection of densely packed cells that processed odor information and at the same time controlled movements.

"Our results are amazing in two ways, " explains Arendt. "First, the cerebrum is much older than anyone imagined, probably the same age as the higher animals themselves. And secondly, we now know that this particular structure evolved in adaptation to life in the Precambrian seas." The Precambrian period is the age from the Earth's birth about 4.6 billion years ago to the beginning of the Cambrian, about 540 million years ago.

So far it had been assumed that the fungus bodies of invertebrates and the cerebrum of vertebrates have developed independently. "The evolutionary history of our cerebrum needs to be rewritten, " summarizes Arendt. display

Detlev Arendt (European Molecular Biology Laboratory, Heidelberg) et al .: Cell, Vol. 142, No. 5, p. 5267 ddp / science.de - Christine Amrhein

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