(ORDO NEWS) — Based on information about single cell RNA, the scientists compiled a detailed atlas of 233 types of neurons in the bearded dragon’s brain.
The authors compared the results obtained with data on the mouse brain and concluded that the brain of reptiles and mammals contains a mixture of ancient (common to both) and specific neurons.
Thus, the evolution of the vertebrate brain did not look like the appearance of new parts without changing the previous ones.
Scientists at the Max Planck Institute for Brain Research in Frankfurt, Germany, have created a molecular atlas of the brain of the bearded dragon lizard ( Pogona vitticeps ) and compared it with that of the mouse brain.
The results of the study disproved the popular belief that the mammalian brain consists of an ancient “reptilian” brain, supplemented with new features.
In fact, both reptile and mammalian brains have evolved their own new types of nerve cells from a common ancestral set of neurons.
About 320 million years ago, early vertebrates came to land and the first tetrapods appeared, which are now represented by amphibians, mammals, reptiles and descended birds.
Due to the common origin, the brain of all tetrapods has a similar structure, formed at an early stage of their evolution.
However, until now it has remained unclear exactly how different clades (groups of organisms containing a common ancestor and all its direct descendants) acquired their characteristic features.
Neurons are the most diverse cell type in the body. Their diversity reflects the changes that have taken place in the process of evolution.
For example, some areas of the brain do not work separately from each other: this suggests that they also evolved together.
Previously, there was a hypothesis that new parts of the brain were added to the old ones in the process of evolution.
This idea was rejected, but scientists still believed that some areas of the brain that evolved from the same ancestral structure in reptiles and mammals might have changed little in one clade and become more “modern” in another.
On the other hand, the brains of both clades may contain a mixture of ancient and newer types of neurons.
To determine which concept was correct, the scientists examined neuronal transcriptomes by sequencing the RNA of single cells.
These molecules are transcribed on the DNA template and contain the instructions for making proteins, so the set of RNA that each cell contains makes it possible to assign it to one type or another.
Based on these data, scientists have created a detailed atlas of different types of bearded dragon brain cells.
In total, the researchers analyzed 280,000 agama brain cells and identified 233 different types of neurons. Further processing of the data showed that these cells can be grouped into common families based on transcriptomes.
At the same time, most areas of the brain contained a mixture of ancient (common for mice and agamas) and specific types of neurons.
The thalamus, a part of the diencephalon that performs a number of important functions, such as the transmission of sensory and motor information and the regulation of circadian rhythms, attracted special attention of scientists.
The thalamus is part of the so-called reptilian brain, but scientists have shown that all of its neurons can be divided into two transcriptomic and anatomical domains.
At the same time, one area was similar in reptiles and mammals, while the other has changed greatly in the process of evolution.
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