The development of ependyma in the human fetal brain: an immunohistological and electron microscopic study.

The stratified inner layer of the embryonic fetal brain, the ventricular zone (VZ), contains glial fibrillary acidic protein (GFAP)-positive cell bodies of radial glia. The adult cerebral ventricle is lined by a single layer of cuboidal, ciliated common ependymal cells which are, immunohistologically, GFAP negative. In late gestation, the ventricular lining is formed by tanycytes, ependymal cells with short, intensely GFAP-positive basal fibres. The development of ependyma was examined, morphologically and immunohistologically, in human fetal brain from between 11 weeks gestation to 6 months post-term to determine the relationship between the radial glia cell, tanycyte and common ependymal cell. This study was not able to show whether tanycytes were formed from radial glia or were formed from a previously uncommitted population of VZ cells. The study did show, however, that tanycytes probably mature into common ependymal cells following acquisition of cilia and loss of basal fibres. Electron microscopic data indicate that tanycytes have features suggestive of a secretory and/or transport function.