Fig. 4. Mesendoderm can rescue AD hypothalamus and neurogenesis in MZoep embryos. Views of wild-type embryos, MZoep embryos or MZoep embryos injected in one blastomere at the 16-cell stage with either tar* RNA or tar*+XFD RNA together with nls-GFP or nls-lacZ RNA as lineage tracers. Genotype+injected RNA indicated top right. Probes and antibodies indicated in the bottom right-hand corner. (A-C) Frontal views of live embryos with GFP labeled rescued mesendoderm visible (green). Cyclopia is rescued in B. (D-F) Lateral views of brains with anterior towards the left showing expression of the endodermal marker foxa2. Expression in the brain (arrowhead) is at the zona limitans intrathalamica. (G-I) Lateral views (G,H) and transverse section (I) of brains showing absence/presence of hypothalamic markers. The rescued AD hypothalamus (black arrowheads) and the ß-gal-positive endodermal tar*-expressing cells (arrow) are indicated. Expression of emx2 in G,H (asterisks) is in the dorsal brain (primarily telencephalon). (J) Schematic showing experimental approach in which MZoep cells expressing GFP and lacZ RNA are transplanted into the tar*-expressing domain of a tar* mRNA injected MZoep host. (K) Transverse section of a brain from an embryo that underwent the experimental procedure outlined in J. The transplanted cells (brown nuclei) contribute to the rescued hypothalamus stained with nk2.1a (blue). (L-N) Frontal views of embryos labeled to show Hu immunoreactive neurons in the ventral forebrain (white arrowheads). In N, neurons are restored above the rescued mesendoderm (GFP green). (O,P) Ventral views of brains labeled to show TH immunoreactive ventral diencephalic neurons. These neurons are absent in MZoep embryos (not shown) but are restored in the mesendoderm-rescued embryo shown in P. h, hypothalamus; l, lens; r, retina, t, telencephalon, zli, zona limitans intrathalamica.