Local abolition of BDNF-promoted branching by EphA7–Fc in the stripe assay. Substrates containing alternating lanes of EphA7–Fc versus Fc (A) or Fc versus Fc (B) were prepared according to standard procedures (Hornberger et al., 1999; Knöll et al., 2001a) and overlaid with laminin/merosin. Then single retinal cells from the nasal third of E8 retinas were plated onto this carpet and incubated for 4 d in the presence of 20 ng/ml BDNF. A, On an EphA7–Fc versus Fc substrate, primary axon growth was not affected, but axons showed a bias against branching on EphA7–Fc containing stripes. Stripes labeled in red contain EphA7–Fc. B, On a control substrate containing Fc versus Fc lanes, axons showed no bias in their branching behavior. For a quantification of these data, see details given in Results. Scale bar, 10 μm.