The Study Of Neocortical Lamination And Cell Cycle In Mouse

The brain's surface is cerebral cortex which is constituted by the gray matter where the nerve cells are concentrated. The cerebral cortex is divided into allocortex and isocortex,or as the neocortex. The structure of allocortex is simple.The cerebral cortex of reptiles is mainly constituted by allocortex, while 90% of mammalian cerebral cortex is neocortex. The neocortex contains two primary types of neurons, excitatory pyramidal neurons (80% of neocortical neurons) and inhibitory interneurons. The development of cerebral cortex is closely related to neuronal proliferation, migration and differentiation. Cell cycle has an important role in the regulation of brain size, the occurrence of tissue, neural stem cell differentiation and maintenance. At present people made penetrating research on its morphous, cell chemical construction, fiber contact, neurotransmitter and the mechanism of different neuroapoptosis. But the data about characteristics of cell proliferation and relationship of cell cycle and cell migration and its specific protein expression during the development in cerebral cortex is relatively less. With the problem is clarified, it will deepen the understanding of law during the nervous system development, and it will offer necessary help for some catagenetic nervous system disease.Objective: To investigate the formation of lamination and development of pyramidal cells, the rules of cortical neurons proliferation and the relationship between cell cycle and migration with the characteristics of specific protein expression during the development of mouse cerebral cortex.Methods: The immunofluorescent stainings, DiI tracing and 5-bromodeoxyuridine (BrdU) assay were used to observe the changes in embryonic and postnatal mice cerebral cortex, and density of BrdU and CyclinD1 positive cells on cerebral cortex were measured.Results:â‘ After postnatal day 0 (P0), the lamination of deep cortical layers (VI-V) start, the trend of lamination of superficial cortical layers (IV-II) began after P5, the six layers were fully formed at P7. Developed to P14, the feature of lamination in cerebral cortex was fully formed, then stabilized at P30. In the process of lamination, pyramidal cells were oval-shaped and had small branches with their dendritics at E17. At P15, the pyramidal cells were mature and appeared with complex apical dendrites and base dendrites.â‘¡BrdU is the specific marker of proliferating cells in S phase. From P0 to P30, the density of BrdU-positive cells decreased in cerebral cortex, proliferating cells density was the highest at P0. Cell density decreased estimating CUB curve and the difference about proliferating cells has statistical significance during the development in mouse cerebral cortex, P<0.05.â‘¢CyclinD1 and CDK4 is the specific protein in G1-S phase.The density of CyclinD1 positive cells was the highest at P12 and lower at P0 and P30. Cell density increased firstly then decreased estimating CUB curve. The difference about CyclinD1 positive cells has statistical significance during the development in mouse cerebral cortex, P<0.01. The expression of CDK4 positive cells were continued in mouse cerebral cortex from P0 to P30, and reduced gradually after P60.Conclusions: The laminating neocortex experiences are mainly cells proliferation,differentiation and migration. It was an important period for the lamination in cerebral cortex from P0 to P30, the six layers of neocortex had been formed at P7, the structure of lamination was mature at P30. The development of lamination in neocortex followed"inside-out"pattern, meanwhile, the pyramidal cells were gradually mature. During the development of lamination, neural stem cell proliferation gradually decreased with age. These proliferating cells were progenitor cells and glial cells which are in S phase. Active period of cell proliferation was from P7 to P14, the active period of their migration was from P7 to P14. These migrating cells were mainly glial cells in G1 phase. The migration of cortical neurons reached a peak at P12.