BRCA-1 is a tumor suppressor gene that plays a role in DNA repair and cellular growth control. Here we show that BRCA-1 mRNA is expressed by embryonic rat brain and is localized to the neuroepithelium containing neuronal precursor cells. The expression of BRCA-1 decreases during rat brain development, but BRCA-1 is expressed postnatally by proliferating neuronal precursor cells in the developing cerebellum. Neural stem cells (NSC) prepared from embryonic rat brain and cultured in the presence of epidermal growth factor were positive for BRCA-1. Induction of NSC differentiation resulted in down-regulation of BRCA-1 expression as shown by RNA and protein analyses. In addition to embryonic cells, BRCA-1 is also present in NSC prepared from adult rat brain. In adult rats, BRCA1 was expressed by cells in the walls of brain ventricles and in choroid plexus. The results show that BRCA-1 is present in embryonic and adult rat NSC and that the expression is linked to NSC proliferation. (C) 2003 Wiley-Liss, Inc.