Fig. 1. Localization of Par3 (A-D) and aPKC (E-H) in preimplantation mouse embryos. (A) Par3 (red) localizes to apical cell surfaces (arrow) at the 8-cell stage. (B-D) Three optical sections of the same blastocyst at 5 µm, 24 µm and 42 µm showing concentration of Par3 at apico-lateral surfaces of cells (arrowheads). DNA is stained blue. (E,F) aPKC is concentrated at apical cell surfaces (arrow on this glancing optical section) and nuclei (arrowhead) at the 8-cell stage. (G,H) Confocal sections of the same blastocyst at 14 µm and 26 µm showing concentration at outer apico-lateral cell borders (arrowheads). The inset to panel H shows a mitotic spindle in a dividing blastomere revealed by staining of aPKC (red), Par3 (green) and DNA (blue). Bar, 10 µm.