Prominin-1 (CD133) is a cholesterol-interacting pentaspan membrane glycoprotein specifically associated with plasma membrane protrusions. Prominin-1 is expressed by various stem and progenitor cells, notably neuroepithelial progenitors found in the developing embryonic brain. Here, we further investigated its expression in the murine brain. Biochemical analyses of brain membranes at early stages of development revealed the expression of two distinct splice variants of prominin-1, s1 and s3, which have different cytoplasmic C-terminal domains. The relative abundance of the s3 variant increased toward adulthood, whereas the opposite was observed for the s1 variant. Our combined in situ hybridization and immunohistochemistry revealed the expression of prominin-1 in a subpopulation of Olig-2-positive oligodendroglial cells present within white matter tracts of postnatal and adult brain. Furthermore, immunohistological and biochemical characterization suggested strongly that the s3 variant is a novel component of myelin. Consistent with this, the expression of prominin-1.s3 was significantly reduced in the brain of myelin-deficient mice. Finally, oligodendrocytes expressed selectively the s3 variant whereas GFAP-positive astrocytes expressed the s1 variant in primary glial cell cultures derived from embryonic brains. Collectively, our data demonstrate a complex expression pattern of prominin-1 molecules in developing adult brain. Given that prominin-1 is thought to act as an organizer of plasma membrane protrusions, they further suggest that a specific prominin-1 splice variant might play a role in morphogenesis and/or maintenance of the myelin sheath. © 2008 Wiley-Liss, Inc.