Fig. 2. Chemorepulsion of olfactory tract axons caused by Slit2 but not by the septum is inhibited in the presence of soluble Robo/Fc. E14.5-15 olfactory bulb explants were co-cultured with either aggregates of Slit2-expressing cells (A-C), E14. 5-15 septal explants (D-E) or alone (G-I) in collagen gels in the absence (A,D,G) or presence of Robo1/Fc conditioned medium (B,E,H) or Robo2/Fc conditioned medium (C,F,I). The cultures were incubated at 37°C for 24-48 hours and examined by phase contrast microscopy for axonal outgrowth of olfactory tract axons.