Ectopic Lrrn2 can cause misrouting of axons. (A) Schematic to show experimental approach. On the left is shown a HH10 chick embryo with electrodes positioned on either side of the hindbrain. DNA is injected into the neural tube and following electroporation is expressed unilaterally on the side of the positive electrode. After 48 h embryos are harvested and the retrograde dye DiI is injected into BA2. Dye travels along axonal processes and labels the cell bodies from which they originate. (B, B') Flatmounted hindbrain from a control embryo electroporated with pCAβ-eGFPm5 shows motor projections to BA2 labelled by retrograde DiI injection. (B) Overlay of artificially coloured DiI fluorescence (red) showing BA2 axons and a brightfield photograph of the hindbrain. (B') Overlay showing strong GFP expression in r2 and r3 on the left side of the hindbrain. All axons projecting to BA2 clearly originate in r4 and r5 with no cell bodies lying anterior to the r3/4 boundary. (C, C') Embryo with misexpression of Lrrn2-GFP in r2/3 shows several ectopic axons that project from cell bodies in r3 to BA2. (C") High power views of the boxed region in (C') showing that the ectopic axons originate from Lrrn2-GFP+ cells (red arrows). Scale bars: 100 μm.