ACIDIC FGF AND FGF RECEPTORS ARE SPECIFICALLY EXPRESSED IN NEURONS OFDEVELOPING AND ADULT-RAT DORSAL-ROOT GANGLIA

Employing complementary technical approaches, we have studied the expr ession of acidic fibroblast growth factor (aFGF) and FGF receptors in rat dorsal root ganglia. The results clearly showed that within spinal nerves aFGF and two high-affinity FGF receptors, FGFR-1 and FGFR-2, w ere prominently expressed in neurons, while expression in Schwann cell s was undetectable. FGFR-3 and FGFR-4 were not expressed in dorsal roo t ganglia, Acidic FGF mRNA was detected in the majority of dorsal root ganglion neurons, including all size classes; FGFR-1 and FGFR-2 trans cripts were only detected in subpopulations of mainly large and medium size neurons. In subcellular fractionation studies on dorsal root gan glion and spinal root tissue, aFGF was recovered in the soluble fracti on and was thus not tightly associated with neuronal membranes. During development FGFR-1 and FGFR-2 mRNAs were found to be present at all s tages examined (embryonic days 15-21 and postnatal days 1-120). Acidic FGF mRNA and protein were first detected at embryonic day 18, and the ir expression then increased progressively up to postnatal levels, In cultures of dorsal root ganglion neurons derived from day 15 embryos, aFGF expression was first detected 3 days after plating. The resulting neuron cultures continued to express aFGF in a Schwann cell-independe nt manner. In combination, these results indicate that aFGF expression in dorsal root ganglia is initiated and maintained in postmitotic neu rons. Furthermore, the data suggest that the physiological function of aFGF in the peripheral nervous system is connected to processes speci fic to the mature sensory (and motor) system, such as the maintenance and survival of peripheral nerve neurons.