[Background]
The human brain is highly developed compared to other animals, thanks to which humans are believed to have acquired special abilities. One of the important factors considered to contribute to the development of the brain is the gyrus*1), the fold of the surface of the cerebral cortex*2).
The cerebral cortex is particularly important in higher brain functions. The cerebral cortex of higher animals, including humans, has many folds, called the gyrus (plural: "gyri") (Figure 1). Because of the gyrus, it has become possible for the brain of higher animals to have a large number of neurons, and thus great development of brain functions has been acquired. On the other hand, the mouse, a widely used model animal, has a brain without gyri. This has made it very difficult to do research on the gyrus using the mouse as a model animal; therefore, research on the gyrus has been much retarded.
A research group at Kanazawa University, Japan, has been using the ferret*3), a higher mammal, that has a brain more similar to the human brain than that of the mouse. The ferret brain is known to have gyri, but research techniques for the ferret brain were not well developed. The research group developed a technique for the ferret brain, which allows analysis of ferrets at the genome level, and reported the results using that technique in 2012 and 2013. Thus, this group is a world leader in molecular biological research using the brain of higher mammals, and by using this technique, for example, they succeeded in developing a ferret disease model that shows impairment in gyrus formation. In the present study, using their technique, they have identified a signaling pathway that plays important roles in gyrus formation in the cerebral cortex of higher mammals.
[Results]
The Kanazawa University group has investigated mechanisms involved in gyrus formation during early ferret cerebral cortex development, and identified for the first time that FGF signaling*4) is important in gyrus formation. More specifically, 4 observations have been made.
In summary, it is concluded that FGF signaling augments the number of neuronal progenitors and neurons in regions destined to become gyri, and, as a result, gyri, folds of the cerebral cortex, are formed (Figure 3).
[Significance and future prospects]
In the present study, the authors uncovered an important mechanism of gyrus formation in the cerebral cortex by using their unique research technique developed for the ferret. In the past, there have been few studies on the mechanisms of gyrus formation with animal models, so the present study is truly world leading. As mentioned above, the research group succeeded in 2015 in developing a ferret disease model that shows impairment in the gyrus.
It is expected that further studies along these lines should contribute to research on brain evolution, up to that of the human, which has been difficult in the past, and to the investigation of causes and treatment of various diseases of the brain and the nervous system.
[Glossary]
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