Antibodies to ganglioside G_M1 induce mitogenic stimulation and cap formation in rat thymocytes

Antibodies towards the ganglioside G_M1[galactosyl‐N‐acetylgalactosaminyl‐(N‐acetylneuraminyl)‐galactosylglucosyl ceramide] stimulated DNA synthesis in rat thymocytes. No mitogenic stimulation was observed with the monomeric Fab fragment of anti‐G_M1, suggesting that cross‐linking of the gangliosides or associated components was required for activation by these antibodies. Incubation of thymocytes with anti‐G_M1 and fluorescein‐labeled anti‐rabbit IgG at 0°C resulted in uniform ring‐like or patchy staining that developed into a pronounced cap upon elevation of temperature. The cap had a characteristic uropod form, enriched with intracellular organelles. Sodium azide and cytochalasin B completely inhibited cap formation, while colchicine was without effect. These results imply a possible direct or indirect association between surface gangliosides and submembraneous cytoskeletal assemblies that control modulation of these surface components and may transmit stimuli to the interior of the cell.