Fig. 3. Grafts of BMP2-producing cells obliterate the development of oligodendrocytes in the spinal cord in vivo. Such grafts, however, neither block SHH production nor affect the development of cells of the astrocyte lineage. Pellets of BMP2-overexpressing Q2bn cells or control cells were implanted at E3-E3.5 between neural tube and somites and embryos were fixed at E7-7.5. (A) Section outside the manipulated region in an embryo grafted with BMP2-producing cells. Ventricular O4-positive cells are found in normal position within the ventral ventricular zone, close to the floor plate (fp). (B,C) Embryo grafted with control-Q2bn cells. (B) Dark field/fluorescence view showing the position of DiI-labelled grafted cells (red). (C) Confocal image of the field framed in B, showing O4 immunostaining. Note the normal development of O4-positive cells in the ventral ventricular zone. (D-F) Sections in embryos grafted with BMP2-producing cells. (D) At the level of the graft, shown in red in E, O4-positive cells are totally absent. In particular, they are not found in the ventricular region above the floor plate (fp). (F) Section at the level of the graft in another embryo. There are no O4-positive neuroepithelial cells on the grafted side (right hand side of the micrograph), but some are discernible on the contralateral side (arrowhead). (G-I) Sections stained with anti-Shh antibody. (G) Control section. Floor-plate cells display Shh immunoreactivity. (H,I) Section in an embryo grafted with BMP2-producing cells. (H) Low-power view showing the large mass of grafted cells (red) flanking the lateral wall of the neural tube. (I) Enlargement of the area boxed in H. Distribution and intensity of Shh immunoreactivity in the floor plate appear comparable with those seen in control sections. (J) Control section stained with anti-GLAST antibody. GLAST is expressed at the plasma membrane of neuroepithelial cells and floor plate cells (fp). Dispersed staining is also found in radial fibres and dispersed cells within the mantle layer. (K) Section in an embryo grafted with BMP2-producing cells, stained with O4 antibody. Grafted cells appear in red on the left-hand side of the micrograph. Note that the ventricular region lacks O4-positive cells. A few are discernible in the marginal layer on the contralateral side. (L) Enlargement of the area boxed in K. The section has been counterstained with anti-GLAST antibody. Staining is comparable with that seen in control sections, both in the neuroepithelium and in the floor plate (fp).