The development of animal cap cells in Xenopus: a measure of the start of animal cap competence to form mesoderm

Grafting, together with tissue identification by monoclonal antibodies, has been used to study the allocation of Xenopus animal cap cells to the ectodermal or mesodermal lineages. Animal cap cells become responsive at stage 61 and lose responsiveness to mesodermal induction at, or just after, stage 10i (depending on the batch of embryos). The ability of the vegetal yolky cells to induce mesoderm disappears between stages 10i and 11. It is present at stage 6-6£ and may exist before this. The emergence of competence to respond at stage 6i, coupled with the fact that the endoderm is already capable of induction at this stage, suggests that mesodermal induction begins at this point in the intact embryo.