Fig. 5. Pre-streak stage mouse embryos imaged with epifluorescence and confocal microscopy. Hex-GFP expressed in the AVE is green, nuclei are blue (stained with DAPI) and cell borders are red (stained for actin with TRITC-Phalloidin). Each panel shows a different embryo, with anterior always to the left. (A) An epifluorescence and phase-contrast image of an embryo showing the AVE clearly discernible as a thickening of the visceral endoderm. (B) A 3D-volume rendering of a confocal image stack of an embryo at an equivalent stage, showing the plane at which the confocal sections in panels C and D were acquired. (C) A confocal section through the distal tip of an embryo, illustrating the columnar nature of the single layer of cells at the distal tip. The cells are clearly polarised, their nuclei closer to the epiblast. GFP-expressing and non-expressing cells can be seen intermingled in the AVE. (D) An embryo in which the AVE has started migrating proximally. AVE cells migrate in contact with the epiblast at all times, and are never seen on top of other visceral endoderm cells. Scale bar in D: 40 µm for A; 10 µm for C; 15 µm for D.