Fig. 2. Ectopic domains of ephrin-B1 inhibit/repel the arborization of RGC axons, but do not affect their trajectories. Ectopic domains of ephrin-B1 are marked by the green eGFP reporter and RGC axons and arborizations are labeled red by anterogradely transported DiI. (A'',B'',C'',D'' and E'' are merged images of A and A' etc.) (A-B'') Lateral (L) half of an E14 tectum transfected with RCAS-ephrin-B1-IRES-eGFP. DiI was focally injected into nasal (N) dorsal retina. (A-A'') RGC axons extend without deviation through ectopic domains of ephrin-B1. (B-B'') Close up views reveal that ectopic domains of ephrin-B1 ring the TZ (arrowheads). (C-D'') Ventral RGC axons in tecta transfected with RCAS-ephrin-B1-eGFP. In both cases, a dense TZ is present in the appropriate location. However, the TZs appear to be shaped by the domains of ectopic ephrin-B1-eGFP. (C-C'') Ectopic domains of ephrin-B1 hem in the TZ; dense arborizations of the TZ fill areas with little or no ectopic expression of ephrin-B1 (arrowheads). (D-D'') The TZ is split into a larger and smaller component of dense arborization by an area of sparse arborization coincident with an ectopic domain of ephrin-B1 (arrowheads). (E-E'') A TZ in medial tectum at E13 interspersed with small patches of ectopic domains of ephrin-B1. The tectum was transfected with RCAS-ephrin-B1-IRES-eGFP. The usually uniformly dense TZ is perforated with areas of sparse arborization (arrowheads in E) that in most instances are coincident with ectopic domains of ephrin-B1 (arrowheads in E'). V, ventral. Scale bar in E'': 900 µm (A), 300 µm (B,C,D) and 200 µm (E).