Expression of sox1a and sox1b in tal1, gata3, and gata2a mutants. (A) Cross-sectional schematic indicating positions of KA″, KA′, and V2b neurons. Lateral views of sox1a and sox1b expression in 24 h WT sibling (B,E,H,K,N,Q) and tal1 (C,F), gata3 (I,L), and gata2a (O,R) mutants. Dorsal, top; anterior, left. Dashed lines indicate ventral limit of spinal cord. Scale bar = 50 microns. Mean number of cells expressing sox1a (D,J,P) or sox1b (G,M,S) in each D/V row of spinal cord region adjacent to somites 6–10 in WT and mutant embryos. For tal1 and gata3 mutant results (D,G,J,M) the approximate proportions of medial and lateral row 3 cells are indicated by horizontal lines separating the number of medially-located cells (bottom and indicated with an “M”) from the number of laterally-located cells (top and indicated with a “L”). All of the remaining row 3 cells in these mutants are lateral, consistent with them being V2b cells. All counts are an average of at least 4 embryos. Error bars indicate SEM. Statistically significant comparisons are indicated with brackets and stars. ***P < 0.001, **P < 0.01, *P < 0.05. For P-values see Supplementary Table 3.
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