Fig. 4. Zic2 is essential for EphB1 expression in the VT retina. (A) White dashed lines delineate retinal sections from wild-type (a-a''), heterozygous (b-b'') and homozygous (c-c'') E16.5 littermate embryos. Immunostaining shows that Zic2 (red) is expressed in VT retina (yellow arrows) in Zic2^+/+ mice, but is not detected in Zic2^kd/kd embryos. Some Zic2-positive cells are detected in Zic2^+/kd embryos. (a',b',c') In situ hybridization for EphB1 (green) in the same retinal sections. (a'',b'',c'') Higher-magnification of the respective boxed areas. These images reveal that EphB1 is expressed in the same area as Zic2 in wild-type retinas. In Zic2^+/kd retinas, EphB1 expression is reduced compared with the wild type in accordance with a downregulation of Zic2. In Zic2^kd/kd retinas, in which Zic2 is not expressed, levels of EphB1 are undetectable. d, dorsal; v, ventral. Yellow arrowheads indicate high expression of Zic2 (a,b,c) and EphB1 (a',b',c'). Scale bar: 100 µm. (B) In situ hybridization for EphB1 in horizontal sections from E17.5 Zic2^+/+ (a) and Zic2^kd/kd (b) brains. EphB1 is extensively expressed in a very similar pattern in both genotypes. Lgp, lateral globus pallidus; Cx, cortex; hi, hippocampus; th, thalamus. Yellow arrows indicate high expression of EphB1.