Targeted disruption of GAP-43 in P19 embryonal carcinoma cells inhibits neuronal differentiation - As well as acquisition of the morphological phenotype

GAP-43 is expressed in proliferating neuroblasts in vivo and in vitro, but its role during early neurogenesis has not been investigated. Here we show that neuroectodermal differentiation stimulated by retinoic acid (RA) in th e embryonal carcinoma (EC) line P19 is accompanied by upregulation of GAP-4 3 expression in neuroepithelial precursor cells. In contrast, when upregula tion of GAP-43 expression was prevented in 3 independent P19 lines because of a targeted insertion into the gene, generation of neuroepithelial precur sors was inhibited. Consequently, neuronal number was significantly decreas ed, neuronal morphology was abnormal and fewer than 20% of all neurons were able to initiate neuritogenesis. Extracellular matrix (ECM) was unable to rescue initiation of neuritogenesis in the mutant cells, however those neur ites that were extended responded normally to ECM-stimulated neurite outgro wth-promoting signals. These data suggest that GAP-43 function is required for commitment to a neuronal phenotype as well as initiation of neurite ext ension. However, stimulation of neurite outgrowth by ECM in P19s occurs ind ependently of GAP-43. (C) 2000 Elsevier Science B.V. All rights reserved.