Developmental changes in fibroblast growth factor in the chicken embryo limb bud

Cell proliferation is a major event during early limb development. Significant levels of growth factor activity, as measured by stimulation of DNA synthesis in mouse BALB/c 3T3 cells, were found in extracts of chicken embryo limb buds at early stages of development. Extracts from stage-18 limbs (3 days of incubation) were 2 to 3 times more potent than were extracts from older stages, namely 22-24 (4 days), 26 (5 days), and 28 (6 days). Basic fibroblast growth factor (bFGF) was measured specifically using an RIA, and the amounts of factor obtained corresponded to the activities measured by the 3T3 cell-growth assay. In addition, most growth factor in the extracts bound with high affinity to heparin-Sepharose columns. Western (immunologic) blotting and immunoprecipitation with an antibody specific for bFGF revealed a protein of identical size to bFGF--i.e., 18 kDa, in the extracts. Thus, a growth factor with the properties of bFGF is present in the early limb, and the level of this factor is highest when proliferation is a predominant cellular event in the developing limb. These and other data suggest that fibroblast growth factor is a key regulatory factor in embryonic growth and morphogenesis.