The brain is the most important organ of the human body and probably the most complex object in the universe. During the evolution, the cortex of the human brain increased significantly, providing a structural basis for various advanced cognitive functions. Decoding the development of the human brain will provide us with a close-to-essential answer to how “human beings are human”. In exploring the question of why the human cerebral cortex can become larger, people often focus on the gray matter regions in which neurons are concentrated.
In fact, the white matter of the cerebral cortex has also increased dramatically during evolution. Compared with the skin white matter of rodents such as mice, the skin white matter of the human brain has 3000 times the volume of white matter.
In a recent study published online in the leading academic journal Cell, scientists have revealed the important mechanisms by which the human brain expands in the area of white matter during embryonic development. “This finding could help us better understand the development of the human brain’s cortex and provide a basis for exploring the pathogenesis and treatment of diseases associated with white matter damage.” The study’s lead author and co-author, Dr. Wei Huang, said.
Two of the study’s authors, Dr. Huang Wei and Professor Arnold Kriegstein (Photo Source: Study Authors)
In the cerebral cortex, white matter is the area where nerve fibers are concentrated, consisting mainly of neuroxics with myelin, which connect various regions of the brain and are essential for the normal functioning of the brain. White matter damage is associated with a variety of diseases, which are common in diseases caused by abnormal skin development and, in severe cases, can lead to cerebral palsy.
In white matter, oligodendrocyte plays an extremely important role. These cells form the myelin that wraps neuronal axons, promoting the jumping conduction of nerve signals. They are also the largest cell types in white matter, meeting the need to increase myelin formation during a dramatic expansion of white matter.
Previously, some scientific teams used mice and other animals as models to gain a basic understanding of how few protrusion cells are produced and differentiated. However, the brain structure of rodents is, after all, very different from that of humans, what are the special developmental properties of the less protrusion cells in the human brain? The answer to this question is particularly important. That’s the breakthrough in this study.
There are huge differences in brain structure between humans and mice (Photo: MSU Human Brain Atlas, Brainmaps.org)
In this work, the researchers used antibodies from cell surface proteins to enrich stem cells in the cerebral cortex of human embryos, combining single-cell sequencing, brain chip culture, and real-time microscopy to enable type-specific fluorescent markers, genealogy tracking, and genetic mutations in different stem cells in the human cortex.
They have observed that a class of glial cells, endemic to primates, with outer radioglial glial cells (oRG), not only helps to produce large numbers of neurons in the gray matter of the brain, but also provides an additional source of protrusion glial cells for white matter in the human brain.
In addition, in the late pregnancy, the protrusion precursor cells (OPC) undergo continuous symmetrical division, expanding their numbers exponentially, in preparation for the production of a large number of protrusion-less glial cells. Interestingly, the new large number of OPC seis peri-exclusive, moving in the opposite direction, to avoid local accumulation, to ensure a wide distribution of the effect.
The study authors concluded that the three properties of additional sources, continuous division and rapid diffusion significantly increased the number of protrusion cells produced, thus promoting the expansion of white matter in the cerebral cortex.
This study diagram.
It is worth mentioning that the study authors in the discussion part of the paper also pointed out that in the past, the study of microcephaly and other epithelial developmental abnormal diseases tend to focus on neurons, with little consideration of glial cell development abnormalities. “However, our study found that clinically reported disease-causing genes were not only expressed in neurons, but also had higher levels of expression in protrusion precursor cells.” “This suggests that the primary role of glial cells in these genetic diseases is noteworthy, ” Dr. Huang said. “