TCF/Lef:H2B-GFP reporter expression in pre-streak stage embryos. Laser scanning confocal images of (A-B, D) E5.5-E5.75 TCF/Lef:H2B-GFP and (C) Hex:GFP embryos. (A, B) H2B-GFP in TCF/Lef:H2B-GFP embryos was localized to the VE in E5.5 embryos, and colocalized with VE marker HNF4α. (A, A') Prior to DVE specification GFP is detected in a subset of VE cells. (B, B') After initiation of DVE migration (B5, yellow arrowhead) GFP is localized in the majority of VE cells, showing varying levels of GFP expression. (C) Cer1 as a marker of AVE- Cer1 localization overlaps with AVE-specific GFP reporter in Hex:GFP embryos (C3, C'3; yellow arrowhead) (D) A group of GFP positive cells (white arrowhead) localized posteriorly (A1, D1), in relation to Cer1 (AVE, yellow arrowhead) localized anteriorly (D3; AVE, yellow arrowhead). Each row represents one embryo. Panels depict single optical sections (A, B, C, D), or 3D reconstructions (A', B', C') of confocal z-stacks. Green, TCF/Lef:H2B-GFP, Hex:GFP; red, Cer1, HNF4α; blue, Hoechst. Scale bar: 20 μm.