(A–C) Section immunohistochemistry of the mouse retinas labeled with Aldh1a1, Aldh1a3 and glutamine synthetase (GS) antibodies. (A) At E12.5, Aldh1a1 (green) and Aldh1a3 (red) are expressed in dorsal and ventral neural retina (NR), respectively. At the dorsal edge (white box), Aldh1a1 is expressed only in NR, not in RPE (right upper panel), while some RPE cells are Aldh1a3-positive (right lower panel). (B) At E17.5, Aldh1a1 (green) is expressed in the dorsal half and the ventral edge of the retina, but no Aldh1a1-positive RPE cells were detected in the dorsal (right upper panel) and ventral (right lower panel) regions. (C) At 8 weeks, Aldh1a1 (green)-positive cells were double-labeled with GS (red) at the dorsal, boundary, and ventral edge regions (see Figure 1—figure supplement 1A, B; for the ‘boundary’ region). ONL, outer nuclear layer; INL, inner nuclear layer; GCL, ganglion cell layer. (D) Dissected eyeballs and choroidal flat-mounts of adult (8-week-old) wild-type (WT) and Aldh1a1–/– mice. Loss of pigmentation was observed in the dorsonasal region (red arrowhead) of Aldh1a1–/– eyes. (E) Hematoxylin and eosin (H and E) staining of WT and Aldh1a1–/– retinal sections. The pigmented layer (choroid) of the dorsal Aldh1a1–/– retina is thinner than those on the other sides. ONL, outer nuclear layer; IS/OS, inner segment/outer segment; RPE, retinal pigment epithelium; Chd, choroid. (F–H) Quantitative evaluation of choroidal thickness (F), retinal thickness (G), and the length of outer segments (H) of the H and E-stained retinal sections. Data represent the average ±SD; n = 8–9 from 4 to 5 mice per group. *p<0.05. N.S., not significant. [Scale bars, 50 μm (A and C), 200 μm (B), 1 mm (D), and 20 μm (E).].