Fig. 2. Chemotaxis is independent of cell type. (A) The identity of cells that chemotax in response to TGF or HB-EGF (1 ng/ml) was determined in E12 rat cortical explants infected with EGFR virus. MAP2 was used to identify neurons, S-100ß and GFAP were used to distinguish astrocytes. EGFR-infected cells that chemotaxed (labeled with anti-ß-gal in B,D; arrows) expressed the neuronal marker MAP2 in C or the astrocyte marker GFAP in E (arrows). To determine whether any of the cells that chemotax were stem cells, explants were dissociated after 3 days in ligand and the ability of EGFR-infected cells to divide in response to EGF (0.1-1 ng/ml) to generate neurospheres was assessed after 10 days (A), as described in the Materials and Methods. Approximately 25% of the EGFR-infected cells that chemotax could generate neurospheres, a characteristic of stem cells.