Basic fibroblast growth factor affects neuronal migration and differentiation in normotypic cell cultures from the cochleovestibular ganglion of the chick embryo.

To study the role of basic fibroblast growth factor (FGF-2) in the development of sensory neurons, the cochleovestibular ganglion of the chicken embryo provides a well-characterized structure. This permits use of morphological markers in a cell culture preparation comparable to the normal embryo (normocytic). Otocysts were explanted from white leghorn embryos at Hamburger-Hamilton Stages 14-16, when ganglion cell precursors normally start migrating from the otic epithelium. The cultures were supplemented with either fetal bovine serum or human recombinant FGF-2 (in defined medium or serum) for 2 or 5 days. FGF-2 increased explant growth, neuroblast migration, and neurite outgrowth 2- to 10-fold in the first 2 days. Neuronal morphology appeared within 2-3 days with FGF-2 but required at least 4-5 days with serum. FGF-2 in defined medium stimulated early migration and differentiation, but without serum led to degeneration after 5 days. In serum, growth was later and slower but continued for at least 3 weeks. When explants were cultured in serum with a neutralizing antibody to FGF-2, but no FGF added, neuroblast migration and elongation were decreased by 2- to 4-fold, compared to serum alone. Immunocytochemistry demonstrated FGF receptor sites on the migrating ganglionic neuroblasts, on their processes and growth cones, and in the incipient ganglion and otic epithelium at Stages 15-17, both in the embryo and in vitro. The findings suggest that FGF-2 stimulates early migration and differentiation of ganglion cells by activating the receptors of neuroblasts or their precursors in the embryonic otocyst. However, other factors must sustain their later development.