Figure 1
From: Regionalisation of the mouse visceral endoderm as the blastocyst transforms into the egg cylinder
Formation of the extra-embryonic region of the egg cylinder. (A-D) Bright field images of mouse conceptuses, before implantation at E3.5 (A), and after implantation at E4.7-E5.0 (B-D). Arrowheads point to the polar trophectoderm, later called extra-embryonic ectoderm (from pre-egg cylinder stage). White arrows show the visceral endoderm. b, blastocoel ; e, epiblast ; EEC, early egg cylinder; i, inner cell mass (ICM) ; IB, implanted blastocyst ; m, mural trophectoderm; PEC, pre-egg cylinder. (E-G) Phalloidin-Texas red staining (red) of H2B-GFP (green) transgenic conceptuses, showing respectively the membranes and nuclei of cells. Confocal sections of conceptuses at the implanted blastocyst (IB in E), pre-egg cylinder (PEC in F) and early egg cylinder (EEC in G) stages are shown. Yellow arrows show the parietal endoderm. The contour of the epiblast is highlighted in white. Insets show the contour of 3 neighbouring cells of the polar trophectoderm. (H) Measurements of the embryonic region (Emb) and total length of conceptuses at E4.7-E5.0, as defined by the coloured double arrows in B-C. The average number is shown and error bars indicate the standard deviation from 12 implanted blastocysts, 18 pre-egg cylinder and 24 early egg cylinder conceptuses. The ratio between the two lengths is represented in brown. pc, proamniotic cavity. Conceptuses are oriented with the proximal and distal poles respectively up and down. (I-K) Confocal sections of E4.8-E5.0 conceptuses stained with phalloidin-Texas red, showing the distribution of actin. Arrowheads point to an enrichment of actin in a folded region of extra-embryonic ectoderm (exe). The contour of the epiblast is highlighted in yellow. ve, visceral endoderm. (L-N) Bright field images of E4.8-E5.0 conceptuses. Arrowheads point to the folding of the polar trophectoderm. (O) Schematic summary showing the characteristics of conceptuses ordered by stage during the formation of the extra-embryonic region. The polar trophectoderm (grey) thickens and folds, whereas the primitive endoderm (yellow), which initially covers the epiblast (implanted blastocyst stage) and mural trophectoderm (pre-egg cylinder stage), engulfs the extra-embryonic ectoderm at the early egg cylinder stage. Scale bars 20 μm.