We previously demonstrated that choroid plexus epithelial (modified ependymal) cells (CPECs) differentiated into astrocytes after grafting into the spinal cord. In the present study, we examined whether CPECs from rats at postnatal I day (P1), 7 day (P7), and 8 weeks (P8W) can function as neural progenitor cells that give rise to neurons and glial cells. Cell spheres were produced in cultures of whole tissue of the choroid plexus from the fourth ventricle of rats at each postnatal period. P-tubulin class III (Tuj-1), glial fibrillary acid protein (GFAP)-, and O4-positive cells differentiated from cell spheres in the differentiation medium. We produced a monoclonal antibody 3E6 specifically labeling microvilli of CPECs. Using this monoclonal antibody, CPECs were isolated from the choroid plexus of P8W rats by cell sorter (FACS). Immunocytochemistry confirmed that there was no contamination from fibroblasts, endothelial cells, macrophages, or Schwann cells in the FACS-isolated 3E6-labeled cells. Cell spheres formed in the cultures of these 3E6-labeled CPECs. After expansion, these cell spheres gave rise to Tuj-1- (5%), GFAP- (45%), and O4-positive cells (0.16%). The remaining cells (45%) were unlabeled neural or glial markers. Some CPECs of the P8W rat were immunohistochemically stained with lineage-associated markers of Musashi-1 and epidermal growth factor-receptor (EGF-R). In addition, infusion of EGF or fibroblast growth factor-2 (FGF2) into the ventricle increased the number of bromodeoxyuridine (BrdU)-positive cells among CPECs from 0.03% (untreated) to 1.14% (38-fold, EGF) and 1.03% (35-fold, FGF2), respectively. These findings indicate that neural progenitor cells exist among CPECs in the rat. (c) 2005 Wiley-Liss, Inc.