Xenopus laevis is widely used as a model for early vertebrate development. The early Xenopus embryo forms two distinct halves, the pigmented animal pole and the yolky vegetal pole. Fertilisation occurs in the animal pole and this triggers a displacement of the egg cytoplasm.
Cleavage is faster in the pigmented animal pole.
At this stage, the animal pole cells are fated to become epidermal tissue, the marginal zone will become mesodermal and neural tissue and the yolky vegetal cells are specified to an endodermal fate. Gastrulation is initiated at the future dorsal side of the embryo, underneath the organiser region. A blastopore is formed by the invagination of local endodermal cells. The animal pole cells undergo epiboly and converge at the blastopore. Arrows indicate major cell movements.