Fig. 4. Chemorepulsion of spinal motor axons caused by floor plate-derived chemorepulsive activity is not inhibited in the presence of soluble Robo1/Fc. E12 basal plate explants were co-cultured with E12 floor plate explants in collagen gels in the absence (A) or presence (B) of Robo1/Fc conditioned medium. The cultures were incubated at 37°C for 24-48 hours and examined by phase contrast microscopy for chemorepulsion of spinal motor axons growing out of basal plate explants.