The fate of cells in the tailbud of Xenopus laevis

The vertebrate tailbud and trunk form very similar tissues. It has been a c ontroversial question for decades whether cell determination in the develop ing tail proceeds as part of early axial development or whether it proceeds by a different mechanism. To examine this question more closely, we have u sed photoactivation of fluorescence to mark small neighborhoods of cells in the developing tailbud of Xenopus laevis. We show that, in one region of t he tailbud, very small groups of adjacent cells can contribute progeny to t he neural tube, notochord and semitic muscle, as well as other identified c ell types within a single embryo. Groups averaging three adjacent cells at a later stage can contribute progeny with a similar distribution. Our data suggest that the tailbud contains multipotent cells that make very late ger m-layer decisions.