Fig. 4. Effect of Shh on the development of OPCs. Engineered ES cells were treated and selected as described in Fig. 1. On day 10, after 4 days of selection, Shh was added to some of the cultures, all of which were maintained in FGF-2, without G418 or Ganciclovir. After 5 more days, OPCs were identified either by in situ hybridization to detect Olig1, Olig2 and PDGFR mRNAs or by immunohistochemistry to detect NG2 (A). The nuclei in the bottom panels were stained with bisbenzimide. The scale bar is 20 µm. (B) Table showing the proportion of labelled cells. Randomly selected fields were counted in two experiments.