Fig. 2. Regionalized expression of Smad3 depends on patterning genes. (A,C,F,I,L) Comparative expression analysis of Smad3 and progenitor class I/II genes at rostral levels of the chick neural tube at stages 12-18. (B) Diagram showing the expression pattern of selected class I/II genes in ventral progenitor domains. (D,E) Misexpression of Nkx6.1 (D) leads to a decrease in Smad3 in a position-dependent manner (E). Smad3 is repressed from intermediate and dorsal domains, but not from the p3 domain, filled arrow in (E). (G,H) Misexpression of Olig2 (G) leads to a decrease in Smad3 (H), including the p3 domain, open arrow in (H). (J,K) Misexpression of Nkx2.2 (J) induces ectopic expression of Smad3 along the DV axis (K). (M,N) Misexpression of Irx3 (M) induces Smad3 expression within the pMN domain (N). (O) Summary of regulatory interactions between class I/II proteins that prevent the maintenance of Smad3 expression in the pMN domain.