Fig. 3. Lineage tracing of e2+ (A-D) or e2- (E-H) four-cell blastomeres (marked in blue) to the blastocyst stage. (A-D) Series of optical sections of four blastocysts in which the e2 blastomere is labelled with blue dye. The red cells are progeny of one two-cell blastomere labelled with red dye that was first to divide to the four-cell stage. All cells have green nuclei due to the GFP-H2B transgenic marker. In all cases, the vegetal membrane of the labelled four-cell blastomere had not undergone displacement during its generation. In all four cases the blue labelled clone occupies predominantly the mural trophectoderm and does not contribute to ICM. The one exception is the embryo in B, in which a single blue cell was found in the superficial layer of the ICM. The arrowhead in B indicates a fluorescent bead that is retained in the development of this embryo. The bead, which was attached to the vegetal part of the two-cell stage blastomere still remains attached to a blue cell and so continues as a vegetal marker. (E-H) Series of optical sections of four blastocysts in which a vegetally labelled e-blastomere was found in the e1 position and the e2 cell was labelled with blue dye. In all four cases, the blue-labelled clone occupies predominantly the more superficial cells of ICM and also adjacent polar and mural trophectoderm. Scale bar: 18 µm.