Fig. 2.

Zebrafish hoxa3a can substitute for mouse Hoxa3 in thyroid, ultimobranchial body, tracheal epithelium, and soft palate development. Transverse (A–L; dorsal is up) or sagittal (M–P; anterior is up, dorsal is to the left.) paraffin sections of newborn animals; genotypes apply to each column. Scale bars apply to each row. (A–D) The thyroid isthmus (arrow) is deleted in Hoxa3^null/null (^−/−) mice (B), but restored in Hoxa3^zf/zf (zf/zf) (C) and Hoxa3^mz/mz (mz/mz) (D). (E–H) Transverse sections of newborn mice stained with anticalcitonin antibody (brown). Integration of ultimobranchial body–derived C cells is restored in zf/zf (G) and mz/mz (H) mice. (I–L) The disorganized tracheal epithelium in the Hoxa3-null mutant (J) was not seen in zf/zf (K) or mz/mz (L) animals. The white bar in each panel shows the thickness of the WT epithelium, contrasted with the null mutant (long bar in J). (M–P) The posterior palate (velum) is shortened in Hoxa3-null mutants (N), but is normal in zf/zf and mz/mz mice (M, O, and P). tr, trachea; es, esophagus; pa, palate; to, tongue. (Scale bars: 200 μm in A–D; 100 μm in E–H; 50 μm in I–L; 800 μm in M–P.)