Sorting out of cells from different parts and stages of the chick limb bud.

To examine differences in the surface properties of progress zone cells of avian wing buds, we mixed cells from the "progress zone" at different stages. To identify the origin of cells, a chick-specific antibody was used in a mixed culture of chick and quail cells, or cells from one of the stages were labeled with a fluorescent dye, PKH-24. Within 18 hr in mixed culture, cells segregated from each other and formed patches of various sizes. The segregation occurred independently of chondrogenic aggregation, but chondrogenesis occurred later in the center of the patches. Similar segregation was observed in mixed cultures of cells of the anterior progress zone, the posterior progress zone, the anterior subdistal region, and the posterior subdistal region. These results suggest that surface properties of cells in the progress zone and subdistal region change during limb bud development and vary along the anterior-posterior axis of the limb bud.