Fig. 10. Neutralising Shh activity in explant cultures of ventral spinal cord. Stage 12/13 (E2) chick neural tube was dissected into dorsal, intermediate and ventral thirds. The ventral thirds were cultured in collagen gels in the presence of either control antibody (A,C) or with neutralising anti-Shh antibody (B,D). Explants were double-labelled with O4 monoclonal antibody (C,D) and anti-Gfap (A,B). Anti-Shh blocks the formation of O4-positive OLPs but not Gfap-positive astrocytes. Scale bar: 10 µm.