spt mutants possess more posterior mesoderm. (A) Expression at 16.5 h of hoxb6b, arrowhead indicates the extent of anterior staining within the tailbud mesoderm. (B–D) Expression at 18 h of: (B) hoxd13a, (C) hoxc11b, and (D) hoxb8a, arrowheads indicate extent of staining in the cloaca (B) or in the pronephros (C and D). (E–I) Expression at 19 h of: (E) wt1a and (F) gss, marking anterior segments and (G) jag2 and (H) pax2a, marking posterior segments. Arrows indicate label in the most anterior nephric segment and brackets indicate regions that are altered. Embryos are shown from a (A–D and G, H) left side view, or (E, F) dorsal view with anterior to the left.