Fig. 6. Effects of expression of dominant-negative Robo1 and Robo2 constructs in chick hindbrains. (A-J) Flat-mount chick hindbrains that have been electroporated with plasmids encoding myristylated GFP (myr-GFP), dominant-negative Robo1-GFP (Robo1-GFP) or Robo2-GFP (Robo2-GFP) as labelled. Hindbrains were fixed at stage 17-19 and immunostained with anti-Islet 1/2 antibodies to detect motoneuron cell bodies (red), while GFP expression is shown in green. (F,I-N) Preparations additionally immunostained using anti-neurofilament antibodies (blue) to reveal all axon tracts. (G-J) Asterisks show borders of floor plate. (K-M) Transverse cryostat sections of embryos electroporated with plasmids labelled as above, with insets showing higher magnification. Immunostaining is as above. Yellow and white arrows show dorsal and ventral exit points, respectively. Both dorsal and ventral GFP-labelled motor axons exit in the control whereas only ventral axon projections are present in the dominant-negative Robo-electroporated embryos. (L) The trigeminal ganglion is immunostained in red (Islet 1/2). Scale bar: 100 µm in A-F; 15 µm in G-I; 50 µm in K,L,N; 30 µm in M; 20 µm in insets.