Fig. 8. In vitro blockade of EphB-ephrinB interactions results in the misprojection of commissural axons into dorsal regions of the spinal cord that express B-class ephrins. (A) A combined fluorescence and phase-contrast micrograph of an E11 mouse open-book spinal cord explant in which commissural axons were anterogradely labeled with DiI at 0 hours in culture. In this preparation, a single axon is shown within the floor plate (bounded by white lines). (B) EphB3-Fc appropriately detects B-class ephrin expression in the floor plate and in a dorsal region of cultured E11.5 open-book spinal cord explants. (C-G) Commissural axons were anterogradely labeled with DiI in open-book spinal cord preparations obtained from E11-E11.5 mouse embryos and cultured for 48 hours in the presence of 50 µg/ml Fc alone (C-E), EphB3-Fc (F) or ephrinB1-Fc (G). Each panel depicts only the trajectory followed by commissural axons on the contralateral side of the spinal cord. (C) In explants cultured in the presence of Fc alone, commissural axons grew a considerable distance away from the floor plate and turned at an appropriate position within an intermediate region of the spinal cord white matter. (D,E) At high magnification, the turns executed by decussated commissural axons in C. In explants cultured in the presence of EphB3-Fc (F) or ephrinB1-Fc (G), commissural axons aberrantly projected into more dorsal regions of the spinal cord where B-class ephrins are expressed.
