Fig. 2. Anterior-posterior axis phenotypes of Ldb1 null mutant embryos. (A) Wild-type and (B) mutant E7.5 embryos. A constriction at the embryonic-extraembryonic junction of the mutant embryo is clearly visible (arrows in B). (C-E) E8.5 embryos showing in situ expression patterns of the forebrain marker Six3. Frontal (C) and lateral (D) views of a wild-type embryo, showing heart (arrow) and head (arrowhead) structures. Frontal view (ventral side up, E) of an E8.5 mutant embryo with defects in head and heart development, truncation of forebrain structures and absence of Six3 expression. (F-H) En2 expression that marks midbrain-hindbrain boundary at E8.5 is present in a wild-type embryo (F) but absent in mutant embryos (G,H). (I,J) Krox2 expression marking rhombomeres 3 and 5 in wild-type (I) and mutant (J) embryos. Expression of this gene shows partial duplication of rhombomeres 3 and 5 in the mutant (J). (K,L) Hematoxylin and Eosin-stained horizontal sections of E8.5 wild-type and mutant embryos, respectively. The mutant embryo (L) lacks all head structures anterior of the otic vesicles (arrows). The kinks in the neural tube indicate defective longitudinal extension of the neural epithelium. (M) Hematoxylin and Eosin-stained cross section taken from the trunk level of an E8.5 mutant embryo showing abnormal development of two neural grooves (arrows) within a single continuous neuroepithelial layer. (N,O) Scanning electron micrographs presenting ventral (N) and dorsal (O) views of an E8.5 mutant embryo. Abnormal development of four rows of somites is indicated with arrows. (P,Q) TUNEL staining of histological sections taken from comparable regions of E8.5 wild-type and mutant embryos, respectively. Arrows point to extensive cell death in the mesenchyme, and to a lesser degree in the neuroepithelium, of the mutant embryo (Q). The scale bars represents 100 µm in A-J,N,O; 25 µm in K,L; 10 µm in M; and 2 µm in P,Q.