Lineage analysis of inner cell mass and trophectoderm using microsurgically reconstituted mouse blastocysts

The fate of mouse blastocyst tissues was examined following reconstitution of blastocysts from isolated inner cell mass (ICM) and trophectoderm differing for electrophoretic variants at the glucose phosphate isomerase (GPI-1) locus. A modified microsurgical method was used and a more sensitive enzyme assay allowed finer dissection of developing chimaeric conceptuses. In seven of nine cases, the extraembryonic ectoderm or the later ectoderm of the chorion was entirely of the blastocyst trophectoderm enzyme type, providing the first direct evidence that this tissue can be wholly derived from the trophectoderm. The two exceptions could represent contamination of the ICM with trophectoderm or might indicate some developmental lability of ICM cells. In addition, the results confirm the cell lineages of other tissues of the 7.5- to 9.5-day pc embryo and, for the first time, directly demonstrate the ICM origin of the parietal endoderm.