Expression of Tg(-8.1gata1:gata1-EGFP) in single and double mutants. Lateral views of 30 h Tg(-8.1gata1:gata1-EGFP) WT sibling (A) and single and double mutants as indicated (B–F). Dorsal, top; anterior, left. Dashed rectangle regions in main panels (A–F) are shown in magnified view in adjacent (A′–F′) panels. Dashed lines indicate ventral limit of spinal cord. White arrows indicate KA″ axons, magenta arrows indicate KA′ axons and white arrowheads mark V2b axons. KA″ and KA′ axons are ipsilateral and ascending whereas V2b axons are ipsilateral descending. KA″ neurons appear to form normally and extend WT-like axonal projections in tal1;gata3 double mutants (E,E′). In contrast, even though GFP-expressing V2b cells are present in both gata3 (C,C′) and gata2a (D,D′) single mutants there are no GFP-expressing V2b cells in gata2a;gata3 double mutants (F,F′). Scale bar = 50 microns.