Evolution: possible role of stem cells (promised find) (Evolution)

by David Turell , Thursday, December 12, 2019, 20:40 (1806 days ago) @ David Turell

Special different stem cells may have driven human brain size and specialization evolution:

https://www.ucsf.edu/news/2015/09/131646/stem-cell-research-hints-evolution-human-brain

"The human cerebral cortex contains 16 billion neurons, wired together into arcane, layered circuits responsible for everything from our ability to walk and talk to our sense of nostalgia and drive to dream of the future. In the course of human evolution, the cortex has expanded as much as 1,000-fold, but how this occurred is still a mystery to scientists.

"Now, researchers at UC San Francisco have succeeded in mapping the genetic signature of a unique group of stem cells in the human brain that seem to generate most of the neurons in our massive cerebral cortex.

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"Until recently, most of what scientists knew about this process came from studies of model organisms such as mice, where nearly all neurons are produced by stem cells called ventricular radial glia (vRGs) that inhabit a fertile layer of tissue deep in the brain called the ventricular zone (VZ). But recent insights suggested that the development of the human cortex might have some additional wrinkles.

"In 2010, Kriegstein’s lab discovered a new type of neural stem cell in the human brain, which they dubbed outer radial glia (oRGs) because these cells reside farther away from the nurturing ventricles, in an outer layer of the subventricular zone (oSVZ). To the researchers’ surprise, further investigations revealed that during the peak of cortical development in humans, most of the neuron production was happening in the oSVZ rather than the familiar VZ.

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"The gene activity profiles also provided several novel insights into the biology of outer radial glia. For example, researchers had previously been puzzled as to how oRG cells could maintain their generative vitality so far away from the nurturing VZ. “In the mouse, as cells move away from the ventricles, they lose their ability to differentiate into neurons,” Kriegstein explained.

"But the new data reveals that oRGs bring a support group with them: The cells express genes for surface markers and molecular signals that enhance their own ability to proliferate, the researchers found.
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“This is a surprising new feature of their biology,” Pollen said. “They generate their own stem cell niche.”

"The researchers used their new molecular insights to isolate oRGs in culture for the first time, and showed that these cells are prolific neuron factories. In contrast to mouse vRGs, which produce 10 to 100 daughter cells during brain development, a single human oRG can produce thousands of daughter neurons, as well as glial cells—non-neuronal brain cells increasingly recognized as being responsible for a broad array of maintenance functions in the brain.

"The discovery of human oRGs’ self-renewing niche and remarkable generative capacity reinforces the idea that these cells may have been responsible for the expansion of the cerebral cortex in our primate ancestors, the researchers said."

Comment: It is logical that stem cells must play a major role in speciation, since they are the creators of functional cells. We still don't understand why or how the new stem cells arrived on the scene.