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Fig. 1. Mouse embryos at the periimplantation (A, day 4.5) and post-implantation
(B, day 6.0; C, day 7.0) stages of development, showing the allocation of
derivatives of the inner cell mass/epiblast, primitive endoderm and
trophectoderm, to different tissue compartments of the conceptus. The inner
cell mass is the precursor of the epiblast of day 6.0 embryos, and the
transition between these two tissues is likely to be a progressive process
(Rathjen et al., 2002). The
epiblast gives rise to ectoderm, mesoderm and definitive endoderm. The
primitive endoderm of the day 4.5 embryo is derived from the inner cell mass.
It differentiates into parietal and visceral endoderm (both contribute to
fetal extra-embryonic membranes). The trophectoderm gives rise to the
ectoplacental cone, extra-embryonic ectoderm and the trophoblast giant cells.
The Reichert's membrane is a composite layer of trophoblast giant cells, the
basement membrane and the parietal endoderm.
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