Fig. 3. Effect of combined positive and negative selection on engineered ES cells. Engineered ES cells were treated and selected as described in Fig. 1 to enrich for neuroepithelial cells and to eliminate residual undifferentiated ES cells. At various times, the cells were dissociated, and either stained for SSEA-1 or nestin by immunohistochemistry (A) or processed for RT-PCR analysis using Oct4, Sox1, Sox2 or G3PDH probes (B). The results in (A) are shown as mean±s.d. of four independent experiments.