EXISTENCE OF GRADIENT IN CELL ADHESIVENESS ALONG THE DEVELOPING XENOPUS HIND-LIMB BUD, SHOWN BY A CELLULAR SORTING-OUT EXPERIMENT IN-VITRO

To examine the possibility of a difference in cell adhesiveness along the developing Xenopus hind limb bud axes, single mesenchymal cells fr om developing hind limb buds were cultured, allowing them to form an a ggregate in a gyratory culture system. By observing the distribution o f cells within aggregates, it was found that sorting-out occurred betw een cells from different positions and different stages. Cells derived from more distal positions tended to be situated interiorly in the ag gregates. According to Steinberg's differential adhesion hypothesis, t hese results support the idea that there is a graded difference in cel l adhesiveness along the proximo-distal axis of the developing limb, w ith adhesiveness increasing distally. Although similar sorting-out was observed between anterior and posterior cell populations, it could no t be determined which cell populations were definitely more cohesive. These properties may be correlated with the experimentally demonstrate d 'positional value', which should be different among cells located at different positions along the axes of the developing vertebrate limb bud.