Early Otx2-GFP expression in epiblast and AVE. a. GFP fluorescence and transmission observations of Otx2+/OGand control Otx2+/+embryos at E6.5 and E7.5. Anterior is leftward. Scale bars: 100 μm. b. Direct visualisation of GFP fluorescence (green) and immunofluorescent staining of F-actin (Phalloidin – red) and DNA (Hoechst – blue) on 10 μm thin uterus sections containing E6.5 Otx2+/OGembryo. Green staining in and around the extraembryonic part of the conceptus is not due to GFP fluorescence but to autofluorescence of decidual and blood cells that are present in the tissue. Images on the right correspond to magnification of white box. Arrow indicates the boundary between embryonic and extra-embryonic part of the conceptus. Dotted line delimits the frontier between anterior visceral endoderm (ave) and epiblast (ep). Anterior is leftward. Scale bars: 50 μm.