Cell Lineage and Commitment in Early Amphibian Development

It is clear by the neurula stage of amphibian development that the three primary cell types or germ layers can be recognized. However, little is known about when and how individual cells of the blastula and gastrula become committed to these germ layers. The laser dye tetramethyl rhodamine isothiocyanate is proving a useful cell marker for studies of cell commitment. When labelled cells from the animal or vegetal pole of Xenopus laevis early embryos are transplanted into host blastocoels, their progeny become specified to different germ layers and differentiate in accordance with surrounding cells. By using this method we have shown that animal and vegetal pole cells are pluripotent at the early blastula stage, while vegetal pole cells are committed to form endoderm by the early gastrula stage of development. One population of cells, the primordial germ cells, which arise from the vegetal part of the early embryo, are shown still to be pluripotent at the swimming tadpole stage.