Fig. 2. Defective forebrain and optic development in Raldh2^-/- embryos. (A,A') Serial frontal sections through the forebrain neuroepithelium of a headfold (10 somite)-stage wild-type embryo at the level of the optic evagination (ov) and prospective telencephalon (te). (B,B') Comparative sections of a stage-matched Raldh2^-/- embryo. Brackets indicate regionally disorganized neuroepithelium. There is an excess of overlying mesenchymal cells (ms). (C,D) Comparative frontal sections at an early stage of optic vesicle (ov) development (14- to 15-somite stages). Arrowheads indicate the presence of cell debris in the Raldh2^-/- forebrain lumen. (E,F) Sections at the anterior forebrain level, showing defective telencephalic vesicle outgrowth and excess mesenchymal cells (in the mutant, F). (G-J) Serial transverse sections through the telencephalic (te), diencephalic (di) and optic (ov) vesicles of E9.5 wild-type (G,I) and Raldh2^-/- (H,J) embryos. Insets show details of the mesencephalic (me) neuroepithelium (G,H) and of the distal tip of the optic vesicle and surface ectoderm (se) (I,J). (K-M) Details of the infundibulum (in) and Rathke's pouch (rp) in a control (K) and two Raldh2^-/- (L,M) embryos. pp, prechordal plate. Hematoxylin and Eosin staining.