Fig. 3. Expression of Zic3 mRNA on cross sections of embryonic chick eye. In situ hybridization experiments were performed on the cryosections of embryonic chick eye at various stages: (A) E4.5; (B) E6; (C,D) E9; (E,F) E16. Note that Zic3 mRNA expression is in a periphery-high, center-low gradient at E4.5 and E6 (A,B). At E9, most of Zic3 expression is confined to the retinal periphery (labeled `P' in C,D). Zic3 is also highly expressed in the ciliary margin area (C,E,F). At E16, Zic3 expression can be barely detected inside the retina while at a high level at the ciliary margin (E,F). C, center of the retina; P, periphery of the retina; R, retina; CM, ciliary margin. Arrowhead in C indicates the remaining undifferentiated cells located in the inner nuclear layer that are weakly expressing Zic3 mRNA at the retinal center. Scale bars: 100 µm in A,B,D-F; 400 µm in C.