p57Kip2 expression and function in the AGM. Analysis of p57Kip2 expression by in situ hybridization in E9 wild-type (A-B), E11 wild-type (C-H), and E11 p57Kip2^+/−m (I) embryos. (D) Caudal section; (F) rostral section. (G) Close-up of an E11 aorta with endothelial expression highlighted by arrows and subaortic expression with an asterisk. Stained sections were mounted with Hydromount. Ventral, down. DA indicates dorsal aorta; HG, hindgut; LB, lung bud; NC, nephrogenic chord; and VA, vitelline artery. (J) Graph showing percentage of mice repopulated with E11 and E12 AGMs (1 ee) from wild-type or p57Kip2 mutant embryos. The number of repopulated mice/total mice injected is indicated above each bar. (K) Cytospin of E11 AGM cells stained with an antibody for p57Kip2 (green, Alexa488) and mounted with Vectashield. Nuclear 4,6 diamidino-2-phenylindole staining in blue. White arrowheads indicate cells with cytoplasmic p57Kip2. Expression analysis by in situ hybridization for Cryab (L,Li) and Th (M,Mi) on wild-type (L-M) and p57Kip2^+/−m (Li,Mi) E11 embryos. Stained sections were mounted with Hydromount (National Diagnostics). All pictures were taken with a Zeiss AxioSkop2 Wide-Field Microscope fitted with a Zeiss AxioCam MRc5, and images analyzed with the Zeiss AxioVision software (all from Carl Zeiss Ltd). Objectives used were 5×/0.15 NA (C,H-I), 10×/0.25 NA (A-B,D-F,L,Li,M,Mi), 20×/0.45 NA (G), and 40×/0.65 NA (K).