Fate map for the 32-cell stage of<i>Xenopus laevis</i>

TLDR

The 32‑cell stage of *Xenopus laevis* shows a regular topographic projection that varies among individuals due to cleavage plane variability and short‑range cell mixing during gastrulation, disrupting mapping of anteroposterior dorsal axial structures and short notochord, neural tube, or somite segments. Researchers selected embryos with regular cleavage, injected individual blastomeres with fluorescein‑dextran‑amine, used 3‑D reconstructions of later stages to map clone locations and tissue volumes, and performed orthotopic grafts up to stage 10 to assess morphogenetic movements. A complete fate map for the 32‑cell stage was produced by pooling 107 cases, detailing each blastomere’s tissue fate, composition, and spatial localization.

Abstract

Abstract A complete fate map has been produced for the 32-cell stage of Xenopus laevis. Embryos with a regular cleavage pattern were selected and individual blasto-meres were injected with the lineage label fluorescein–dextran–amine (FDA). The spatial location of the clones was deduced from three-dimensional (3D) re-constructions of later stages and the volume of each tissue colonized by labelled cells in each tissue was measured. The results from 107 cases were pooled to give a fate map which shows the fate of each blastomere in terms of tissue types, the composition of each tissue by blastomere, the location of each prospective region on the embryo and the fate of each blastomere in terms of spatial localization. Morphogenetic movements up to stage 10 (early gastrula) were assessed by carrying out a number of orthotopic grafts at blastula and gastrula stages using donor embryos uniformly labelled with FDA. Although there is a regular topographic projection from the 32-cell stage this varies a little between individuals because of variability of positions of cleavage planes and because of short-range cell mixing during gastrulation. The cell mixing means that the topographic projection fails for anteroposterior segments of the dorsal axial structures and it is not possible to include short segments of notochord or neural tube or individual somites on the pregastrulation fate map.