Figure 4

Fewer Zic2⁺retinal ganglion cells are born in albino than in pigmented ventrotemporal retina at embryonic day 13. (A) Schematic of ventrotemporal (VT) retinal ganglion cell (RGC) production in pigmented retina (adapted from Young [29]). E, embryonic day; P, postnatal day. (B) Timeline of 5-ethynyl-2’-deoxyuridine (EdU) injections (10 am, 2 pm, 6 pm) at E13 and sacrifice at E15.5. Each box represents 4 hours. VT region defined as the most peripheral 800 pixels (1 pixel = 0.3205 μm). (C) Coronal sections of VT retina from pigmented and albino mice injected at E13 with EdU, collected at E15.5, and stained with antibodies to Zic2 and Islet1/2 and processed for EdU detection. All quantifications for (D-F) were carried out in the second and fourth representative sections caudal to the optic nerve. (D) Bar graph comparing the number of Zic2, Islet1/2-double positive cells in the VT region labeled with EdU in the pigmented retina and albino retina. Fewer cells expressing Zic2 and Islet1/2 at E15.5 become post-mitotic at E13 in albino (n = 4) compared with pigmented (n = 4) VT retina. (E) Bar graph comparing the number of Zic2⁻, Islet1/2⁺ cells in VT retina labeled with EdU in pigmented (n = 4) and albino (n = 4) retina. The number of Zic2⁻ RGCs produced at E13 is similar in pigmented (n = 4) and albino (n = 4) retina. (F) Bar graph comparing the number of total RGCs (Islet1/2⁺) labeled with Edu in pigmented (n = 4) and albino (n = 4) retinae. Significantly, fewer cells are Islet1/2⁻ and EdU⁺ in the albino retina. Error bars indicate SEM. Two-tailed unpaired t-test: *P < 0.05, ** P < 0.01. N.S., not significant. Scale bar in (C), 50 μm.