The fate of mouse blastocyst tissues was examined following reconstitution of blastocystsfrom isolated inner cell mass (ICM) and trophectoderm differing for electrophoretic variantsat the glucose phosphate isomerase (GPI-1) locus. A modified microsurgical method was usedand a more sensitive enzyme assay allowed finer dissection of developing chimaeric con-ceptuses. In seven of nine cases, the extraembryonic ectoderm or the later ectoderm of thechorion was entirely of the blastocyst trophectoderm enzyme type, providing the first ditectevidence that this tissue can be wholly derived from the trophectoderm. The two exceptionscould represent contamination of the ICM with trophectoderm or might indicate somedevelopmental lability of ICM cells. In addition, the results confirm the cell lineages of othertissues of the 7·5- to 9·5-day pc embryo and, for the first time, directly demonstrate the ICMorigin of the parietal endoderm.

This content is only available via PDF.