Fig. 7. Smad3 activity promotes differentiation of V0-V2 and V3 interneurons at the expenses of MNs. HH stage 14-16 embryos electroporated with Smad3 were analyzed 48 hours later for the expression of selective LIM-HD factors. (A,C,E,G,I,K) Control embryos showing markers for specific neuronal subpopulations. Lhx3 expression identifies postmitotic pre-migratory MNs and V2 INs. (B,D,F,H,J,L) Forced expression of Smad3 results in the ectopic induction of V2 INs. Lhx3+; Isl1-V2 INs are dorsally and ventrally expanded (F). LMC, lateral MN column; MMC, medial MN column (E). Chx10-expressing V2 INs (I-L) are also dorsally and ventrally expanded. (M,O,Q,S,U)Control embryos showing markers for specific ventral IN populations. (N,P,R,T,V) Misexpression of Smad3 induces Pax2+, En1+ V1 and Evx1+ V0 INs. Ectopic expression of Pax2 (N), En1 (P) and Evx1 (R) is detected ventral to the p2/p1 domain boundary. (S-V) Misexpression of Smad3 induces few ectopic Nkx2.2+ cells (T) and a dorsal expansion of Sim1+ V3 INs (V). (W,X) Diagrammatic representation of ventral progenitor domains and ventral neuronal subtypes, generated in a normal spinal cord and after Smad3 misexpression.