A mechanism identified by a team from the Montreal Clinical Research Institute explains how the human brain reaches its optimal size and why the eyes of mice are smaller than human eyes, a discovery that allows for a better understanding of the evolution of the nervous system.<\/p>\n
This could one day lead to a better understanding of human developmental disorders characterized by abnormal brain size or structure, such as microcephaly or certain cortical malformations, or even to the development of new weapons against cancer.<\/p>\n
\u201cWe already suspected that the way cells divide, that is, in space or in the plane of the tissue, could play a role in the decision to multiply or to produce cells that will form the brain or the retina,\u201d said Dr. Michel Cayouette of the IRCM.<\/p>\n
\u201cAnd so, in this study, we identified two important genes that control the orientation of cell division, that is, along which axis the cells will divide in the tissue.\u201d<\/p>\n
Dr. Cayouette and his colleagues discovered that the direction of neural stem cell division acts as a true cellular \u201cswitch\u201d that determines the final number of cells produced in the brain and retina, it was explained in a press release.<\/p>\n
By changing this orientation, the researchers were able to generate brain and retinal tissues up to 30 per cent larger, even including additional layers of cells.<\/p>\n
\u201cSimply by changing the orientation of the cells, it is enough to increase cell proliferation, and therefore cell multiplication, which means that we end up with tissues that are much larger than normal,\u201d summarized Dr. Cayouette.<\/p>\n
In mice, the division of neuronal and retinal stem cells normally occurs along a generally horizontal axis, a tightly regulated process that limits tissue expansion and helps to fix their final size.<\/p>\n
Dr. Cayouette\u2019s team, however, found that inactivating the GPSM2 and SAPCD2 genes redirects this division along a vertical axis, resulting in the formation of larger tissues.<\/p>\n
In comparison, the human retina and that of the macaque naturally exhibit more vertical divisions of stem cells.<\/p>\n
\u201cIt is suspected that this reorientation of the cell (\u2026) allows for an increase in the \u2018pool\u2019 of stem cells that is used by the tissue to generate more cells, and therefore to control the final size of the tissues that are produced, whether it be a brain or a retina,\u201d said Dr. Cayouette. \u201cIt is quite remarkable that simply changing the orientation in which cells divide allows for control over tissue size.\u201d<\/p>\n
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