Stanford Study Reveals Brain Develops From Two Separate Nervous Systems
- Stanford Medicine researchers published a study in Nature Neuroscience on September 18 revealing that the human brain develops from two distinct, ancient nervous systems that never mix.
- During gastrulation, the early embryonic stage when tissue organizes into three layers, researchers identified two separate populations of neural ectoderm instead of a single type.
- Cell identities remain fixed because chromatin, the DNA packaging system, keeps different genetic instructions open or sealed shut in each group.
Stanford Medicine researchers published a study in Nature Neuroscience on September 18 revealing that the human brain develops from two distinct, ancient nervous systems that never mix. Lead authors Rayyan Jokhai and Carolyn Dundes found that the front and back parts of the brain originate from entirely separate progenitor cells, overturning centuries of scientific consensus that viewed the organ as one unified structure.
Embryo Gastrulation Creates Two Separate Starter Cell Populations
During gastrulation, the early embryonic stage when tissue organizes into three layers, researchers identified two separate populations of neural ectoderm instead of a single type. The first group, known as anterior neural ectoderm, switches on the Otx2 gene to form the forebrain and midbrain. The second group, posterior neural ectoderm, activates the Gbx2 gene to build the hindbrain, which controls automatic life functions like breathing and swallowing. Kyle Loh, senior author of the study, noted that anterior cells arise from a totally different progenitor cell than posterior cells.
Chromatin Packaging Locks Cell Identities Permanently
Cell identities remain fixed because chromatin, the DNA packaging system, keeps different genetic instructions open or sealed shut in each group. Anterior cells maintain open pages for forebrain genes while locking hindbrain genes shut, and posterior cells exhibit the exact opposite pattern. This structural division was established days before actual brain regions formed, explaining why previous laboratory attempts to convert forebrain starters into hindbrain cells under those conditions failed.
Human Hindbrain Motor Neurons Grown in the Laboratory
Capitalizing on these findings, the Stanford team guided human pluripotent stem cells step by step into the posterior neural ectoderm to produce human hindbrain motor neurons. These lab-grown cells produced acetylcholine, fired action potentials, and expressed appropriate genes to control face and throat muscles used in swallowing and speech. This development provides a new model for studying conditions like amyotrophic lateral sclerosis and spinal muscular atrophy, where these specific motor neurons fail and patients lose vital functions.
Evolutionary Analysis Tracing the Two-Part Brain Plan
Evolutionary analysis revealed the same distinct cellular split in chickens, zebrafish, macaques, and acorn worms, indicating that the two-part brain plan predates vertebrates by more than 550 million years. Jellyfish, which diverged 600 to 700 million years ago, lack a centralized brain entirely and possess two separate nerve nets at opposite ends of the body. While the spatial compression of these two systems in ancestral species likely provided communication and modular evolutionary advantages, further research is required to test those hypotheses.