Fig. 2. Neuroepithelial cells and residual ES cells in non-selected ES-cell-derived cultures. ES cells were cultured as shown in Fig. 1 but without selection. At various times, the cells were dissociated, allowed to settle on a coverslip for 6 hours and stained for SSEA-1 or nestin by immunohistochemistry. The proportion of stained cells was determined, and the results are shown as mean±s.d. of three independent experiments.