p57Kip2 is expressed in SA progenitor cells. (A) Schematic depiction of maturation stages in the SA lineage as defined by listed marker expression. Underlined markers were used in immunohistochemistry in panel B. (B) Immunohistochemical staining of E11 wild-type embryo cryosections for p57Kip2 (red), Sox (green), Phox2b (green), Gata3 (green) and Th (white), with 4′,6-diamidino-2-phenylindole (DAPI) as nuclear counterstain (blue). Close-ups of boxed areas in merged images are shown. White scale bars equal 10 μm and red bars equal 100 μm. D, dorsal; V, ventral.