Dynamics of membrane-cortex contacts demonstrated in vivo in Amoeba proteus pretreated by heat

Abstract

The dissociation of membrane-cortex contact in the fronts of moving amoebae, which was earlier stated mainly in the fixed material is now demonstrated in vivo and cinematographically recorded in living cells pretreated for 15-30 minutes at 40°C. The cells round up and then, when they are cooled at room temperature, the cortex completely dissociates from the membrane and envelops the granuloplasm aggregated in the cell centre, whereas a hyaloplasmic ring, 40-50 μm broad, develops along the whole periphery. Such cells, called by us the hyalospheres, are viable and manifest various intracellular movements, and may eventually recover the capacity to locomote. New cortical layers are rebuilt under the cell membrane, periodically separated from it at 5-10 second intervals, and retracted as optically dense sheets across the hyaloplasmic ring toward the granuloplasmic core. Their separation may be spontaneous, but is strongly promoted by some agents increasing the membrane mobility, which in normal amoebae induce the formation of new fronts of locomotion. The formation of endocytotic invaginations, channels and vacuoles is also easily observed within the large and clear hyaline zone. Some new forms of them are described. The cyclic endocytotic activity is repeated at the steady frequency by the same spots at the cell surface. The hyalospheres may serve as simplified models to investigate in vivo the membrane-cortex interactions involved in the mechanisms of motor behaviour and endocytosis in amoebae.