skor2 is expressed by V0v cells and this expression is lost in evx1;evx2 double mutants. Lateral views of zebrafish spinal cord at 27 h (a) and 30 h (b-d). Anterior left, dorsal top. a & b Merged images on top followed by single-channel views. Panels on RHS are single confocal planes of white dashed-box regions. Stars indicate double-positive cells. a Expression of skor2 (red) and EGFP (green) in Tg(evx1:EGFP) SU1 embryo. In this example, all ventral skor2-expressing cells co-express EGFP. On average, 97 % of ventral skor2-expressing cells co-express EGFP (73/75 cells counted in 4 embryos). In contrast, about 57.5 % of V0v cells co-express skor2 (73/127 cells counted in 4 embryos). b Expression of skor2 (red) and EGFP (green) in Tg(slc17a6:EGFP) embryo that labels glutamatergic cells. Crosses indicate cells that are only clearly positive for skor2. On average 93.5 % of skor2-expressing cells co-express EGFP (201/215 cells counted in 4 embryos). As there is usually a delay in EGFP expression it is possible that all ventral skor2-expressing cells are excitatory V0v cells, as the small number of ventral skor2-positive EGFP-negative cells may be just starting to express EGFP. c & d Expression of skor2 (blue) in both WT (c) and evx1;evx2 double mutant (d) embryos. The ventral row of skor2 expression is lost in double mutants. e Average number of cells (y-axis) expressing skor2 in spinal cord region adjacent to somites 6-10 in WT embryos and evx1 and evx2 single and double mutants (x-axis) at 30 h. Results are shown for the ventral (V0v) domain of skor2 expression and for the whole skor2 expression domain (total cell counts). Values are mean +/- standard deviation (also see Table 1). In each case at least 5 embryos were counted. Statistically significant differences (P < 0.05) from WT values are indicated with stars. P values for all comparisons are provided in Table 1. Scale bar: 50 μm (a & b); 40 μm (c & d)
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