Eph receptors and ephrins are expressed in progenitors of the ventral spinal cord. a. Schematic representation of the ventral spinal cord at E10.5. Progenitors are located in the ventricular zone, three progenitor domains are shown: p2, pMN and p3. Differentiated motor neurons (MN) are located laterally in the mantle zone. b-d. Expression of EphB1 (b), EphB2 (c) and EphB3 (d) was monitored by in situ hybridization on transverse sections of E10.5 embryos. Scale bars: 50 μm. e-g. Transverse sections of E10.5 embryos were immunostained to detect EphA4 ((e), red), EphB2 ((f), blue) and differentiated neurons (Tuj1, green in (g)). Scale bars: 40 μm. (h-p). Expression of Efnb1 (h-j), Efnb2 (k-m) and Efnb3 (n-p) was monitored by in situ hybridization on transverse sections of E9.5, E10.5 and E11.5 embryos, as indicated. Scale bars: 50 μm. Brackets indicate domains of Efnb2 expression in progenitors. FP: floor plate, NC: notochord.