States of determination of single cells transplanted between 512-cell Xenopus embryos.

Single cells from 512-cell Xenopus embryos, totally labeled with intracellular horseradish peroxidase, were transplanted orthotopically (from either dorsal or lateral marginal zone) or heterotopically (between these two marginal zones) to unlabeled host embryos at the 512-cell stage. At tailbud stage 23 the locations, numbers, and histotypes of labeled cells were recorded. The transplanted cell had divided many times, giving rise to labeled progeny that expressed a wide range of cell types and were located in several different organs. Locations and cell types of progeny derived from orthotopic grafts to the dorsal marginal zone were different from those derived from grafts to the lateral marginal zone. Single cells grafted heterotopically to either dorsal or lateral positions expressed fates that were appropriate to their final grafted positions, and not to their original positions. We conclude that individual cells of the marginal zone at the 512-cell stage have multiple presumptive fates and have not been committed to any single fate.