Repression of Tbx2 and Tbx5 expression by exogenous Noggin. (A) Post-culture embryo showing Tbx5 expression in the non-treated dorsal optic cup. (B) Contralateral Noggin-treated eye, showing absence of Tbx5 expression in the optic cup. (C) Post-culture embryo showing Tbx2 expression in the non-treated dorsal optic cup. (D) Contralateral Noggin-treated eye showing a reduced Tbx2 expression domain. Tbx5 expression (E, F) and Tbx2 expression (G, H) are not altered in non-operated and BSA-treated eyes respectively of post-culture embryos. A'-H' show higher magnifications of eyes in A-H. Arrows indicate boundaries of gene expression domains. Implanted beads are marked by asterisks. (I-P) Serial transverse vibratome sections through the optic cup showing altered morphology after Noggin treatment, with the dorsal-most sections in upper panels. (I-L) Post-culture non-treated eye showing invagination of the presumptive neural retina (P-NR) in the ventral optic cup. (M-P) Contralateral Noggin-treated eye showing dorsal extension of the optic stalk region as compared to the non-treated eye. (Q) Schematic representation of normal Tbx2 and Tbx5 expression domains in a lateral view of the optic cup, and the dorsal shift of the expression domains induced by exogenous Noggin. Scale bars: A-H, 0.5 mm; I-P, 0.1 mm. Abbreviations; MN, mandibular process of the first branchial arch; MX, maxillary process of the first branchial arch; N, nasal process; P-NR, presumptive neural retina; OS, optic stalk.