Fig. 4. Shh signaling from the basal plate is required for ZLI induction in D1/2 explants. (A) Strategy to test the requirement for Shh signaling from the basal plate. The ventral part of the basal plate was removed and incubated for 1.5 hours at 37°C with or without MAb-5E1. The basal-plate grafts were cultured in conjunction with D1/2 explants for 48 hours and ZLI differentiation was monitored by Shh expression. (B) D1/2 explant controls. The ZLI-inducing activity of the basal plate (C) was blocked by pre-incubation of basal-plate tissue with MAb-5E1 (D).