Fig. 7. BMP4 abolishes Shh-mediated induction of oligodendrocytes. Ventral neuroepithelial explants were dissected from E5 embryos, before oligodendrocyte induction has occurred. They were grown for 2 days or 7 days in the absence or presence of Shh, with or without BMP4, and stained with O4 antibody (A-C) or with anti-PLP/DM20 antibody (E-G). (A-C) When isolated at E5, the ventral neuroepithelium is unable to generate oligodendrocytes, as shown by absence of expression of O4 antigen (A). In the presence of 12 nM Shh, such explants generate numerous O4-positive cells within 2 days (B). However, explants treated simultaneously with 12 nM Shh and 0.6 nM BMP4 failed to generate O4-positive cells (C). (D) Quantification of the number of O4-positive cells developing in ventral neuroepithelial explants. Bars represent the mean±s.e.m. of at least 12 separate explants. Oligodendrocyte production is maximal with 12 nM Shh. Note that BMP4 totally blocks the Shh-mediated induction of oligodendrocyte formation, irrespective of Shh concentration. (E-G) Confirming the above results, E5 ventral neuroepithelial explants do not generate PLP/DM20-positive oligodendrocytes after a week in culture (E). Shh treatment induces the development of PLP/DM20-positive cells, which display typical oligodendrocyte morphology (F). Again, SHH/BMP double treatment results in the absence of oligodendrocyte development (G).