Ganglioside GM1 alters neuronal morphology by modulating the association of MAP2 with microtubules and actin filaments.

In previous studies, we demonstrated that the exogenous ganglioside GM1 increased the complexity of the microtubular network and level of tubulin, selectively changed the distribution of microtubule associated protein-2 (MAP2) immunoreactivity from the perikarya to distal neuritic processes and increased immunogold label of MAP2 in the subplasmalemmal cytoplasm, neuritic filopodia and growth cones of Neuro-2a neuroblastoma cells. Since these areas are rich in actin filaments, our data suggested that MAP2 may be associated with microfilaments in the early stages of ganglioside-induced neuritogenesis. To determine if GM1 alters neuronal morphology by facilitating the interaction of actin and MAP2, we examined the immunolocalization of these two proteins with confocal and electron microscopy. We found that along with the redistribution of MAP2 from perikaryal to neuritic regions, there was parallel redistribution of actin. The uniform subplasmalemmal actin meshwork was disrupted in areas of processes and filopodia with a redistribution of actin to these areas in close association with MAP2. Our present results suggest that gangliosides enhance neuritogenesis by redistributing actin as well as MAP2 to processes and filopodia thereby facilitating their interaction. The association of MAP2 with actin filaments is likely to be an early step in ganglioside-mediated filopodia formation.