Clonal Restriction Boundaries in Xenopus Embryos Shown with Two Intracellular Lineage Tracers

Abstract

It has been proposed that clonal restriction boundaries develop in Xenopus embryos between clones initiated at the 512-cell stage, and that these boundaries result in formation of morphological compartments, each populated by progeny of a group of ancestral cells. Although this hypothesis has gained some acceptance, it has also been criticized because the use of only one cell lineage tracer was not a conclusive test of the hypothesis. However, the critical experiment, an assessment of the extent of mingling between two labeled clones in the same embryo, has now been performed. A model of the proposed arrangement of the ancestral cell groups in the 512-cell embryo predicted that the two clones would remain separate in 49% of cases and intermingle in 51% of cases. In fact, there was a bimodal distribution, in which separation of the clones occurred in 46% of embryos and extensive interclonal mingling was observed in 54%. These results are not compatible with hypotheses in which a unimodal distribution of mingling would be predicted but are consistent with the compartment hypothesis.