Fig. 5. Induction of En1 and Islet2 at r7 level in the Pax6 mutant by exogenous Pax6. (A-E) pCAX-mPax6 was introduced into the hindbrain of wild-type embryos at the 22-somite stage, and the embryos were cultured for 26 hours (corresponding to E12.5). (A) The same photograph as in Fig. 4A showing distribution of Pax6 protein. (B-E) These sections are adjacent to those shown as Fig. 4A-F, which were obtained from the same embryo. Ectopic expression of Chx10 and En1 is not observed (C,D), while Islet2 expression is relatively downregulated (B). Ectopic expression of Evx1 is observed (arrowheads in E) in the region where Dbx1 is ectopically expressed (compare with Fig. 4F). (F-J) pCAX-mPax6 was introduced into the hindbrain of Pax6 mutant rat embryos at 22-somite stage, and the embryos were cultured for 30 hours (corresponding to E12.5), as neuronal differentiation is slightly delayed in the mutant. (F) The same photograph as in Fig. 4G showing Pax6 expression. (G-J) These sections are adjacent to those shown as Fig. 4G-L, which were obtained from the same embryo. Although Islet2-positive cells are undetectable in both unelectroporated and electroporated sides (G), expression of En1 is recovered in the area where pCAX-mPax6 was electroporated (arrowheads in I). (H) The number of Chx10-positive cells is relatively decreased but sometimes observed at an ectopic position (arrowhead). (J) Evx1-positive cells are observed not only in the normal position (arrow) but also in ectopic positions (arrowheads), where Dbx1 is ectopically expressed (compare with Fig. 6L). (K-P) pCAX-mPax6 was introduced into the hindbrain of Pax6 mutant rat embryos at E10.75, and the embryos were cultured for 42 hours (corresponding to E12.5). (L,N,P) Higher magnifications of K,M,O, respectively. By electroporation into E10.75 Pax6 mutant hindbrain, a small number of SM neurones expressing Islet2 (M, N) and HB9/MNR2 (O,P) emerge in the area where Pax6 is transfected (K,L).
