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Fig. 1. Function of Hh and Wnt signals during neural induction, anteroposterior patterning and eye field development. Xenopus embryos were injected into the animal pole of a single blastomere at the 4-cell stage with the indicated constructs and nlacZ mRNA as a lineage tracer (red nuclei on injected right side). (A,A′) Control late gastrula in dorsal view depicting the neural plate marker Sox2 and the epidermal marker Cytokeratin. (B,B′,C,C′) XGli1 mRNA expands neural at the expense of epidermal tissue, while Gli3C′δClaI mRNA causes the opposite effect. (D,D′,E,E′) XWnt3a DNA promotes epidermal and dnXWnt8 mRNA neural development. (G–G′) Control embryos at neurula stage in anterior view (G,G′) and at tail bud stage in dorsal view (G′). Otx2 demarcates the developing cement gland, forebrain and midbrain (horizontal line), FoxG1 the telencephalon, En2 the posterior midbrain, and Krox20 the hindbrain rhombomeres 3 and 5 (bracket). Open arrowhead points to the anterior border of HoxC6 expression in the spinal cord. (H–H′,I–I′) XGli1 mRNA anteriorizes the brain, whereas Gli3C′δClaI causes very subtle posteriorization. (J–J′) XWnt3a DNA has posteriorizing activity. The arrow points to an expansion of Krox20 expression in neural crest cells. (K–K′) dnXWnt8 mRNA leads to anteriorization. (M) Control tail bud embryo in anterior view, showing Rx2A expression in the bilateral eyes. (N–O) XGli1 mRNAs diminish, whereas Gli3C′δClaI mRNAs expand the eye anlage. (P,Q) XWnt3a DNA leads to a smaller and dnXWnt8 mRNA to a larger eye anlage. (F,L,R) Summary of effects of Hh and zygotic Wnt signals on neural induction (F), anteroposterior patterning (L), and specification of the eye field (R). The indicated gene expression patterns were obtained in: B, 43/46; B′, 24/26; C, 48/49; C′, 41/52; D, 36/40; D′, 17/19; E, 57/57; E′, 64/68, H, 9/10; H′, 12/12 (FoxG1), 8/12 (En2); H′, 7/7 (Krox20), 11/11 (HoxC6); I, 11/13; I′, 18/20 (FoxG1), 15/20 (En2); I′, 17/26 (Krox20), 45/49 (HoxC6); J, 44/44; J′, 34/34 (FoxG1), 29/34 (En2); J′, 43/50 (Krox20), 12/17 (HoxC6); K, 42/45; K′, 37/37 (FoxG1), 29/37 (En2); K′, 15/15 (Krox20), 13/13 (HoxC6); N, 8/10; O, 17/20; P, 8/9; Q, 11/11 (Rx2A). |
