Schematized representation of phenotypes. Schematized representation of transverse sections of the spinal cord showing the dorso-ventral position of p3 (blue), pMN (red) and mixed identity (blue/red) progenitors at different developmental stages and in different genetic backgrounds. Cartoons show 1) the evolution of p3 and pMN numbers over time in wild type embryos and 2) the phenotypes observed in Efnb2 and Efnb3 mutants compared to WT at E11.5. Shh gradient (grey) is represented on the left hand side, while domains of ephrinB2 and ephrinB3 expression in progenitors are represented in green and orange, respectively. In Efnb2 cKO and in Efnb2;Shh trans-heterzygotes (not shown), pMN progenitors are fewer while the number of p3 progenitors is increased. Conversely, in Efnb3 KO, less Nkx2.2+ and more Olig2+ progenitors are present. In addition, pMN and p3 progenitors are intermingled in Efnb3 KO.