Expression of Bmp4 , Tbx2, Tbx3 , Tbx5 , and Vax2 during optic cup formation. (A-C) Bmp4 co-expressed with Tbx5 and Tbx2 in the optic vesicle at E9.5 (arrows; 15 somite stage). Black arrowhead in A indicates Bmp4 expression in the surface ectoderm. White arrowheads indicate expression in mesenchyme ventral to the developing eye. (D-F) Bmp4, Tbx5 and Tbx2 expression in the invaginating optic vesicle at E10.5 (24–29 somite stage). (G, H) Bmp4 and Tbx5 expression at E11.5 in the optic cup in dorsal domain 1, shown schematically in I. (J) Tbx5 expression in dorsal domain 1 in an E11.5 dissected optic cup. (K) Tbx3 expression in dorsal domain 1 and its extension into dorsal domain 2 in the temporal neural retina. (L) Tbx2 expression in domains 1 and 2, shown schematically in M. (N) Tbx3 expression in an E11.5 dissected optic cup. (O) Vax2 expression at E11.5 in the ventral optic cup in domain 4. (P) Double labeling of Tbx2 (red) and Vax2 (blue) shows a domain in between domain 2 and domain 4, which does not express either marker, and is designated domain 3, shown schematically in Q. (R) Tbx2 (red) and Vax2 (blue) expression in an E11.5 dissected optic cup, revealing domain 3 in white. Arrows in G-R indicate the boundaries of gene expression domains. Dashed circles in J, N, R demarcate the lens vesicle. A-F are coronal sections. Scale bars: A-F, 0.05 mm; G, H, K, L, O, P, 0.5 mm; J, N, R, 0.1 mm. Abbreviations: L, lens placode; MN, mandibular process of the first branchial arch; NR, neural retina; P-NR, presumptive neural retina; D-V indicates the dorso-ventral axis, N-T indicates the naso-temporal axis.