TCF/Lef:H2B-GFP reporter expression in gastrulating embryos. Laser scanning confocal images of gastrulating embryos from early streak (~E6.5) to early heafold stages (~E7.75). Anterior (A, A'), lateral (B, B') and posterior views (C, C') of an early streak TCF/Lef:H2B-GFP embryo counterstained for actin. Anterior (D, D'), lateral (E, E') and posterior views (F, F') of a late streak embryo counterstained for actin. Anterior (G, G'), lateral (H, H') and posterior views (I, I') of an early headfold embryo counterstained for cell nuclei. Posterior view (J, J') of a headfold embryo and sections (J1-J4) through it along the indicated planes showing GFP expression in the streak and ingressing mesodermal cells. White arrowheads point to mitotic figures. Yellow arrowheads mark blood islands of the yolk sac. Scalebar: 50 μm. ES, early streak; EHF, early headfold; HF, headfold; LS, late streak.