FIGURE 4 | The fate and developmental properties of blastomeres of ME embryos.

a | A scheme of second cleavages when the first blastomere divides meridionally (M, red) and the second, equatorially/obliquely (E). 4-cell blastomeres that result from E divisions have different fates: the 'vegetal' (V, blue) contributes predominantly to mural trophectoderm (TE); the 'animal' (A, green) contributes predominantly to the superficial inner cell mass (ICM), which is closer to the cavity, and to the surrounding trophectoderm. b | Vegetal poles of 2-cell blastomeres marked with a fluorescent bead. c | One of the 2-cell blastomeres was then marked red to identify the first-dividing blastomere. d | The cell from the E cleavage that is furthest away from the polar body (PB) and carries the vegetal bead (arrowhead) is indicated with an arrow. e | In the blastocyst, cell progeny from the vegetal fate (panel d) predominantly populate the mural trophectoderm (red cell progeny populate the embryonic part). f | The cell from the E cleavage that is furthest away from the polar body, but does not carry the vegetal bead is indicated with an arrow. g | Cell progeny from the animal fate (panel f) populate superficial ICM and associated trophectoderm. As a consequence of membrane movement, the blastomere inheriting 'vegetal' components can be distal or proximal to the three remaining blastomeres and the polar body. h | A scheme of the generation of single cell-type chimaeras of 4-cell blastomeres from ME embryos. Products of the early M-division are shown in red; products of the later E-divisions are shown in blue (vegetal) and green (animal).

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