Amazing stuff!
"... But new research ... reveals that what we call the brain is two distinct organs that evolved independently over hundreds of millions of years. ...
"We've shown for the first time that the front of the brain arises from a totally different progenitor cell than the back of the brain," ..."
"... The new research finding shows that the human brain consists of two ancient nervous systems cleverly packaged together — a more primitive part that regulates our hearts’ beating, our breathing and other functions, and another that makes us distinctly human, capable of poetry, mathematics and wondering about our own origins. ...
The researchers’ breakthrough came from studying the earliest moments of embryonic development, during a stage called gastrulation when the body first takes shape. ... discovered that the hindbrain follows a separate developmental path, running in parallel to — rather than branching off from — the pathway that creates the forebrain and midbrain. ...
The team then examined the DNA packaging, or chromatin, in these cells. Chromatin is a way cells determine which genes can be easily accessed and which are bundled away out of reach. What they found was striking:
The anterior neural ectoderm (future forebrain and midbrain) and posterior neural ectoderm (future hindbrain) have fundamentally different chromatin configurations. These differences essentially locked each progenitor cell into its respective fate, like travelers on parallel tracks that never cross. ...
Armed with this knowledge, the researchers for the first time successfully coaxed human pluripotent stem cells (a kind of cell that can create any cell in the human body) to become functional hindbrain motor neurons in the laboratory. These lab-grown neurons displayed all the hallmarks of authentic hindbrain cells: They exhibited waves of electrical activity called action potentials and made proteins that identify the segments of the hindbrain that control facial and swallowing muscles.
Finally, the researchers looked back over 550 million years of evolutionary time. They found the same two-origin brain pattern in chickens; zebrafish; and, remarkably, in acorn worms, tiny creatures living on the ocean floor that share a distant common ancestor with humans. Jellyfish, which diverged from humans about 600 to 700 million years ago, have two nervous systems at different ends of their body. ..."
From the abstract:
"When and how different brain regions diversify from one another remains unresolved. Does a common neural ectoderm progenitor generate the entire brain? Or do multiple neural ectoderm progenitors exist, each restricted to form specific brain regions?
Here our lineage tracing studies of mouse embryos support the latter model. Two parallel brain progenitors emerge simultaneously during gastrulation:
anterior neural ectoderm (forebrain/midbrain progenitor) and posterior neural ectoderm (hindbrain progenitor).
Differentiation of human pluripotent stem cells into anterior or posterior neural ectoderm-like cells revealed these were lineage committed to forebrain/midbrain versus hindbrain fates, respectively.
They harbored diverging chromatin landscapes foreshadowing future forebrain/midbrain versus hindbrain identities. We further differentiated human pluripotent stem cells into hindbrain rhombomere 5/6-specific motor neurons, which were hitherto difficult to generate in vitro.
Hence, we postulate the brain is a composite organ emanating from two lineage-restricted progenitors; these dual progenitors may be evolutionarily conserved across 550 million years from hemichordates to mammals."
Human brain has a split origin, new research suggests
Fig. 1 Anterior and posterior neural ectoderm in vivo and in vitro.
