Mechanisms of the development of neuronal cell society in the central nervous system

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In the developing cerebral cortex, most neurons that are born near the ventricle accumulate in the subventricular zone (SVZ) as multipolar migrating neurons and are then transformed to locomoting neurons prior to entering the cortical plate (CP). When the locomoting cells reach the layer beneath the marginal zone (MZ), we observed that they undergo various dramatic morphological changes, in addition to the termination of migration. For example, they begin to develop apical primitive dendrites and accumulate beneath the MZ, suggesting that they probably start to form new intercellular relationships with adjacent cells and thereby develop an appropriate layer structure. Furthermore, locomoting neurons guided by radial glial fibers in the CP ultimately undergo somal translocation once their leading processes reach the pial surface ("terminal translocation"). To understand the mechanisms that regulate these events, we took several approaches in this study. Firstly, we screened for genes that are specifically expressed in cells in each zone of the embryonic cortical wall: ventricular zone (VZ), SVZ, or cells beneath the MZ. Consequently, we identified approximately 4, 000 genes that are preferentially expressed in the VZ, among which 659 genes are secretory or transmembrane molecules. As for the SVZ and the cells beneath the MZ, we found about 20 genes and 40 genes expressed preferentially in each zone, respectively. We have analyzed the biological functions of some of these genes in this study. To clarify the regulatory mechanisms of gene expression profiles of these molecules in a migratory stage-dependent manner would be important in the future study.