Fig. 1

The level and orientation of transverse sections for control and RA treated embryos are indicated by lines A, B and C, respectively in D. Note the optic stalks (OS) which extend outward from the forebrain are located at the anterior of the eye cups at 24 hpf in both control and RAtreated embryos. A boundary (b), an extension of the optic lumen, divides the dorsal and ventral retinas of RA-treated embryos. (A) The eyecup of a control embryo at 30 hours postfertilization (hpf) with a single pseudostratified retina (R) and lens (L). (B) At 24 hpf, RA-treatment induced an apparent duplicated retina with a dorsal (D) and ventral (V) retina of slightly reduced size. (C) A more anterior section through the duplicated retina along the length of the optic stalk (OS) which extends laterally from the forebrain at 24 hpf (line C in D). The dorsal half of the stalk (Dos) is associated with the dorsal retina (D) whereas the ventral half of the optic stalk (Vos) is continuous with a layer of pigment epithelium (small arrows) which extends along the ventral retina (V). Note that the optic lumen extends between the dorsal and ventral retinal epithelia which creates a boundary (b) between them at the midline of the eyecup. D-V, dorsal-ventral axis; FB, forebrain; y, yolk; bar, 40 µm.