Expression of Tenascin in Neuroepithelial Cells in Developing Rat Telencephalic Pallium

Developmental expression of tenascin in the rat telencephalic pallium was examined immunohistochemically. By the 12th day of gestation （E12）, immunoreactivity showing a fine granular pattern had already appeared within the cytoplasm of neuroepithelial cells, being accentuated in their external segments. Accumulation of labelling was also evident in the cytoplasm of mitotic neuroepithelial cells lining the central canal. On E13, fine granular labelling was also distinct in the internal segments of the cytoplasm of neuroepithelial cells. From E14 onwards, labelling became more intense and increased the number, and accumulating in the entire length of cytoplasm of all cells constituting the neuroepithelium. Accordingly, labelling produced a linear appearence, and was present radially through the neuroepithelium and primordial plexiform layer, i.e., throughout the entire width of the telencephalic pallium. On E16, the linear labelling became more clearly. Especially, the majority of the intensely labelled cytoplasm of neuroepithelial cells coursed perpendicularly in bundles through the internal region of the neuroepithelium, and terminated along the ventricular surface. Immunoreactivity was also present within the radial fibers which extended in the subventricular and intermediate zones and reached the external limiting membrane. From E18 onwards, labelling rapidly less intense and was limited to the cell processes in the neuroepithelium and subventricular zone. After E22, no further labelling was observed. The present study demonstrated that in the rat telencephalic pallium tenascin was expressed in the cytoplasm of neuroepithelial cells from E12 to E17. On the other hand, tenascin was also expressed in the radial fibers on E16 and E17. It was unclear whether the linear labelling in the neuroepithelium continued to the radial fibers. However, all the cells constituting the neuroepithelium were equally immunoreactive for tenascin. It has been previously reported that tenascin is involved in migration and adhesion. However, in the telencephalon, the labelling becomes rapidly less intense after E18, although the neuroblasts still migrate furiously with keeping adhesion to radial fibers. In the course of cerebral cortical development, the stage from E14 to E17 is the most active period of neurogenesis. It may be possible to consider that tenascin play a role in certain mechanism during the active period of neurogenesis