Researchers reached this conclusion by studying mouse embryos at the gastrulation stage — the initial stage of body formation. They showed that the hindbrain, or rhombencephalon, develops along a separate path, rather than from the same cell lineage that forms the forebrain and midbrain.
The authors identified two groups of precursor cells. One expresses the Otx2 gene and gives rise to the forebrain and midbrain, while the other expresses the Gbx2 gene and forms the hindbrain; these populations do not overlap from the earliest stages of development.
According to the scientists, this casts doubt on the theory that the entire brain arises from a single precursor cell at the early stage of the embryo. As the study suggests, such a conclusion may help grow hindbrain neurons in a Petri dish and study their functions.
Using these data, the team for the first time obtained functional hindbrain motor neurons from human stem cells. They demonstrated electrical activity and produced proteins characteristic of hindbrain segments responsible for the muscles of the face and swallowing.
The authors link this approach to the study of spinal muscular atrophy and amyotrophic lateral sclerosis, in which hindbrain neurons gradually fail. The study indicates that in these diseases, patients lose the ability to swallow and breathe.
Researchers traced a similar two-component pattern of brain formation in chickens, zebrafish, and acorn worms, which have a distant common ancestor with humans. In jellyfish, which split from humans on the evolutionary path 600–700 million years ago, the two nervous systems are located at opposite ends of the body, which, according to the authors, points to a very ancient origin of such a division.
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