Figure 9. Effects of ectopic gene expression on retinal axon divergence at the optic chiasm.

Diagrams summarize retinal fiber projection at the optic chiasm after ectopic expression of EphB1, EphB2 and Zic2 in non-VT RGCs. Nearly all GFP⁺ axons cross the midline when GFP alone is electroporated into embryonic retina. A moderate increase in GFP⁺ ipsilateral projections is observed in retina electroporated with GFP+EphB2 (~10%), while RGCs electroporated with GFP+EphB1 display an even greater increase in uncrossed GFP⁺ fibers (~22%). The strongest effect is observed with Zic2, which is capable of converting ~50% of non-VT GFP⁺ RGC axons to an ipsilateral fate. Colored bar represents theoretical relative percentages of ‘pro-crossing’ (orange) and ‘pro-ipsilateral’ (purple) signals in GFP⁺ RGCs.