Reck-immunoreactivity associated with blood vessels in the mouse implantation chamber. (A) Distinct domains in the mouse implantation chamber at around 7 dpc. (B) Reck-immunoreactivity (dark brown) in the AS and DB in a longitudinal section of a 7-dpc mouse implantation chamber. (C) Loop-shaped structures in DB sections doubly stained for Reck (green) and an endothelial cell marker (red) [PECAM; panel 1] or a mural cell marker (red) [SMA, desmin, or NG2; panels 2, 3, 4, respectively] followed by nuclear counter-staining with DAPI (blue signals; panels 2-4). (D) An example of bifurcating vessels in the DB found in serial sections (4 μm-thick) stained for Reck. Red arrows indicate protruding vessel walls (panel 1) which form a contact zone (panel 2) and eventually separate the vessel into two smaller tubes (panels 3, 4). (E) An example of characteristic Reck-positive cells associated with the contact zone. Two adjacent sections were stained with hematoxylin-eosin (H&E) (panel 1) and immuno-stained for Reck (panel 2), respectively. Blue arrows indicate the contact zone. (F) The wedge-shaped cells lying across the contact zone are positive for Reck (panel 1), SMA (panel 2; fluorescent double staining with Reck), and desmin (panel 3; fluorescent staining). Scale bar: B, 100 μm; C, E, F, 20 μm; D, 30 μm.