A new Stanford Medicine study has challenged the long-held view of the human brain as a single unified organ, suggesting instead that it evolved as two distinct organs with separate developmental origins.
Published in Nature Neuroscience, the study found that the front and back of the brain develop from different progenitor cells during embryonic growth. One cell type, which expresses the gene Otx2, forms the forebrain and midbrain. These regions control language, consciousness and abstract reasoning.
Another cell type, expressing Gbx2, develops into the hindbrain, which regulates essential automatic functions such as breathing, heartbeat and sleep.
Senior author Kyle Loh said the research showed for the first time that the front of the brain arises from a completely different progenitor cell than the back.
The researchers found that the two cell populations do not overlap and have different chromatin structures, which keep them on separate developmental paths. This also helps explain why scientists have struggled for years to grow hindbrain neurons in the lab.
The breakthrough allowed the team to successfully convert human pluripotent stem cells into functional hindbrain motor neurons for the first time. That could help researchers study diseases such as spinal muscular atrophy and amyotrophic lateral sclerosis, which damage hindbrain neurons and affect swallowing and breathing.
The same developmental pattern was also seen in chickens, zebrafish and acorn worms, suggesting that it dates back at least 550 million years.
Researchers say the discovery could speed up future regenerative therapies for neurodegenerative diseases.
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