Neuronal differentiation in F9 embryonal carcinoma cells.

F9 line embryonal carcinoma cells were induced to differentiate into neural direction by long-term treatment of monolayer cultures with retinoic acid and dibutyryl cyclic AMP. Bi- and multi-polar cells appeared, expressing acetylcholinesterase and neurofilament proteins but not markers of glial differentiation including GFA-protein. Nerve growth factor combined with both retinoic acid and dibutyryl cyclic AMP greatly enhanced the development of neuron-like morphology and induced expression of immunoreactivity to tyrosine hydroxylase as well as to Leu-encephalin-like peptides. Similarly, serotonin-like immunofluorescence but not substance P-like immunoreactivity was demonstrable in such cultures. In addition, synaptic-like vesicles were often found in the processes. Analysis of matrix expression in neuronally differentiated F9 cells revealed marked increase in laminin production, as judged by immunofluorescence and immuno-electron microscopy, but no demonstrable intracellular staining for fibronectin or type IV collagen. The results with neuronal cells contrast with the expression of all the three matrix components in endodermally differentiating F9 cells in the same cultures.