Fig. 5. Marker analyses of anterior-posterior axis formation. (A-C), Brachyury (T) expression in E7.5 embryos. The embryo shown in B is one of about 60% (32/56) of the Ldb1 mutant embryos in which proximal-distal extension of the primitive streak appears normal. The embryo shown in C represents mutant embryos in which the expression pattern of T is abnomal. In this lateral view we observe a twisted expression domain of T, with seemingly normal distal extension. (D-F) T expression in E8.5 embryos. (D) Wild-type T expression pattern marking the region of the primitive streak (arrowhead) and the notochord (arrow). (E,F), Ldb1 null mutant embryos with two primitive streaks (arrowheads) connected distally. Two notochords are visible as well (arrows). (G-J), Otx2 expression at E7.75 (G,H) and E7.5 (I,J) is restricted in the mutant (H,J) compared to the wild type (G,I). (K,L), Hnf3ß expression in E7.75 embryos. Two posterior expression domains were found in the mutant (L). (K) The wild-type expression of Hnf3ß in anteriorly migrated endomesodermal cells is indicated by an arrow. This expression domain is absent in the mutant embryo (L). (M,N), Lim1 expression at E7.5 showing presence of one node in the wild-type (M, arrow) and two nodes in the mutant (N, arrows). (O,P) Dkk1 expression at mid-streak stage is absent in the mutant embryo (P). (Q,R), Hesx1 expression at E7.75 is not detectable in the ANE of the mutant. The scale bars represent 100 µm.