Figure 2: EphB2 forward signalling alone is important for topographic mapping of RGC axons from the VT retina.

(a) Top, schematic of the site of DiI injection in the dorsal or VT eye labelling RGCs and the expected TZ for their axonal projections in the lateral or medial contralateral SC, respectively. Bottom, dorsal view of a midbrain whole-mount depicting a normal TZ in the lateral SC from a WT mouse injected with DiI in the dorsal retina as verified in the flatmount (insert) and viewed using epifluorescence microscopy. (b) Top, example of a retina flatmount (insert) and SC whole mount from a WT mouse injected with DiI in the VT retina. Of 109 injected WT specimens analysed, only 3 formed one or more eTZs (3%). Bottom, the SC for each specimen that formed at least one eTZ had their eTZs and corresponding primary TZ outlined in the same colour. All outlines of the same genotype, in this case WT, were then superimposed on each other with the primary TZ positioned at the crosshairs of the compass as illustrated. (c) VT injected EphB2^lacZ/+ heterozygotes formed eTZs (arrows) in 7/22 SC analysed. (d) VT injected EphB2^lacZ/lacZ homozygotes formed eTZs (arrows) in 8/13 SC analysed. (e) Graphic summary of the percent of SC that formed eTZs in mice injected with DiI in the dorsal or VT retina. Dorsal injected: WT (1%, n=87), EphB2^+/− (15%, P=0.0437, n=13), EphB2^−/− (0%, n=3), EphB2^lacZ/+ (0%, n=35), and EphB2^lacZ/lacZ (0%, n=25). VT injected: WT (3%, n=109), EphB2^+/− (6%, n=16), EphB2^−/− (21%, P=0.0194, n=14), EphB2^lacZ/+ (32%, P=0.0001, n=22), and EphB2^lacZ/lacZ (62%, P<0.0001, n=13). FET compared mutant groups with WT mice. Statistical significance is denoted by asterisks: *P≤0.05; **P≤0.01, and ***P≤0.001. Scale bar, 500 μm. C, caudal; L, lateral; M, medial; R, rostral.