AbstractRecent studies of adult neurogenesis of the mammalian central nervous system have suggested unexpected plasticity and complexity of neural cell ontogenesis. Redefinition and reconstitution of cell classification and lineage relationships, especially between glial and neural precursors, are an urgent and crucial concern. In the present study, we describe a new monoclonal antibody, A3B10, which was produced by immunizing mice with the membrane fraction prepared from astrocyte‐enriched primary neural cell cultures. Immunohistochemistry of brain sections, including brains from glial fibrillary acidic protein (GFAP)‐deficient mice and primary mixed neural cell cultures, as well as immunoblot analysis and immunoelectron microscopy, have revealed that 1) A3B10 recognizes a majority of cells in ependyma in neonatal and adult rats, 2) A3B10 stains almost all GFAP+ cells and some S100β+ cells in the corpus callosum, 3) A3B10 specifically stains astrocytes in vitro in primary cultures of rat embryonic cerebral hemispheres, 4) A3B10 equally stains ependymal cells of wild‐type and GFAP‐deficient mice, and 5) A3B10 antigen might construct intermediate filament bundles with GFAP and/or vimentin. These data suggested that the antibody labels a wide array of astorcytic‐lineage cells including astrocytes, astrocyte precursors, and neural stem cells. Screening a cDNA library derived from rat embryonic brain has revealed that the antibody recognizes calmodulin‐regulated spectrin‐associated protein 1 (Camsap1). Thus this antibody may provide not only a new marker to identify astrocyte‐lineage cells but also a new target molecule to elucidate the ontogeny, development, and pathophysiological functions of astrocyte‐lineage cells. © 2008 Wiley‐Liss, Inc.