An immunohistochemical study of basic fibroblast growth factor in the developing chick.

An antiserum against basic fibroblast growth factor (bFGF) was characterized by immunoblot experiments and used to investigate immunohistochemically the appearance of bFGF-like immunoreactivity in the developing chick. Crude homogenates of chick embryos at every developmental stage, when subjected to immunoblotting with the use of bFGF antiserum, exhibited a main band with the same molecular weight (18 kDa) as bovine bFGF. With immunohistochemistry, bFGF immunoreactivity (bFGF-IR) was detected exclusively in intracellular components of various tissues at different stages of development; bFGF-IR appeared initially on embryonic (incubation) day 3 (E3) in the myotome, on E12 in the spinal cord and ganglia, on E8 in chondrocytes and osteoblasts of the vertebrae, and on E10 in the esophageal epithelium. Immunoreaction products were present either in the cytoplasm or in the nuclei, depending on the types of individual bFGF-containing cells; developing chondrocytes and cells in the stratum basale of the esophagus exhibited intense immunoreactions exclusively within the nuclei, and the other cells mainly within the cytoplasm. Moreover, bFGF-IR was observed in discrete regions of these tissues at different stages; the epithelium of the esophagus contained bFGF-IR in all layers on E10 to E18 with a superficial-to-basal gradient, but it began to exhibit bFGF-IR only in the stratum basale after E20; and bFGF-IR was more abundant in hypertrophic chondrocytes than in proliferating ones. As chicks aged, bFGF-IR decreased or disappeared in the muscles, vertebrae and esophageal epithelium, but neuronal bFGF increased in intensity until the perinatal period and thereafter remained unchanged.(ABSTRACT TRUNCATED AT 250 WORDS)