Fig. 6

Cells migrating through the posterior midbrain in Slit and Robo mutants are motor neurons. A-C To identify and quantify migrating neurons that have separated from the oculomotor nucleus in Slit and Robo mutant mice on E10.5, open book preparations were antibody labeled with Islet1/2. In wildtype controls, few Islet1/2+ cells were found within the floor plate (A), while numerous Islet1/2+ cells were seen in the floor plate between the left and right oculomotor nuclei in both Slit and Robo mutants (B, C). D The average number of Islet 1/2+ cells located medial to the oculomotor nuclei were counted for each genotype (2 or more litters per genotype). The number of cells medial to the oculomotor nucleus in Robo1^-/-,2^-/- and Slit1^-/-, 2^-/- mutants is significantly more than wildtype controls. There are more Islet 1/2+ cells in the floor plate in Robo mutants compared to Slit mutants (D). Abbrev. Anterior (A), posterior (P). Scale bars, 100 μm, Error bars indicate standard deviation, **P < 0.01, *P < 0.05. (control, n = 5; Robo1 ^-/-, n = 2; Robo2 ^-/-, n = 4; Robo1 ^-/-,2^+/-, n = 2; Robo1^-/-,2^-/-, n = 6; Robo1^+/-, 2^+/-, n = 5; Slit1^-/, n = 2; Slit2^-/-, n = 3; Slit1^-/-,2^+/-, n = 4; Slit1^-/-,2^-/-, n = 9)