Basic FGF maintains some characteristics of the progress zone of chick limb bud in cell culture

The apical region of chick limb buds (progress zone, PZ) is known to be essential for limb pattern formation. In the PZ, the cells are in an uncommitted state and change their positional values under the influence of the apical ectodermal ridge (AER). Using a culture system of chick PZ cells, we have examined the factor(s) which helps to maintain some of the characteristics of PZ cells. It was found that basic FGF (bFGF) stimulated the expression of AV-1 and Msx 1 mRNA, which are rich in PZ cells at early stages, in the cultured PZ cells. These two molecules were rapidly lost in the control culture without the bFGF. Further, bFGF promoted growth and inhibited chondrogenesis of the cultured PZ cells. When quail PZ cells were cultured in FGF medium, harvested, and grafted to the apical region of chick limb buds, in about half of the grafts, the cells distributed to form a long band along the proximodistal axis and participated in normal host cartilage pattern formation as did intact PZ tissues. In contrast, those cultured in the medium without bFGF distributed as a cluster and did not participate in host cartilage pattern formation. The culture with conditioned medium of BRL cells increased the percentage of the grafts participating in normal pattern formation. These results indicate that bFGF helps to maintain some of the characteristics of PZ cells in culture and suggest that bFGF may be a PZ maintenance factor from the AER.