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 dev elopment of sensory neurons, the cochleovestibular ganglion of the chi cken embryo provides a well-characterized structure. This permits use of morphological markers in a cell culture preparation comparable to t he normal embryo (normocytic). Otocysts were explanted from white legh orn embryos at Hamburger-Hamilton Stages 14-16, when ganglion cell pre cursors normally start migrating from the otic epithelium. The culture s were supplemented with either fetal bovine serum or human recombinan t FGF-S (in defined medium or serum) for 2 or 5 days. FGF-S increased explant growth, neuroblast migration, and neurite outgrowth 2- to 10-f old 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 define d medium stimulated early migration and differentiation, but without s erum led to degeneration after 5 days. In serum, growth was later and slower but continued for at least 3 weeks. hen explants were cultured in serum with a neutralizing antibody to FGF-2, but no FGF added, neur oblast migration and elongation were decreased by 2- to 4-fold, compar ed to serum alone. Immunocytochemistry demonstrated FGF receptor sites on the migrating ganglionic neuroblasts, on their processes and growt h cones, and in the incipient ganglion and otic epithelium at Stages 1 5-17, both in the embryo and in vitro. The findings suggest that FGF-2 stimulates early migration and differentiation of ganglion cells by a ctivating the receptors of neuroblasts or their precursors in the embr yonic otocyst. However, other factors must sustain their later develop ment. (C) 1996 Academic Press, Inc.