Redistribution of surface-bound con A is quantitatively related to the movement of cells developing polarity

Capping in cells developing polarity has been reinterpreted on the basis of a quantitative analysis of Concanavalin A (Con A) redistribution and cell movement in Walker carcinosarcoma cells. Several new features emerged. Based on the developing asymmetry in the distribution of surface-bound Con A, the direction of cell movement and the prospective front-tail polarity can already be predicted when the cell is spherical. Development of polarity by an initially spherical cell is associated with formation of two parts. The concentrically contracting part (prospective uropod) characterized by surface-associated Con A decreases in size, while the other part is cleared from Con A and grows into formerly unoccupied space. Surface-bound Con A shows isotropic centripetal movement towards the initial position of the centroid of the spherical cell rather than rearward movement. Therefore, the centroid of fluorescence intensity remains either stationary or moves marginally forward with respect to the initial position of the spherical cell. The amount and direction of cell movement measured correlates closely with values predicted by a theoretical model that assumes a unidirectional transfer of volume from a stationary contracting compartment into a protruding compartment. The results suggest that isotropic (cortical) contraction of the initially spherical cells and one-sided relaxation rather than unidirectional retrograde movement of ligand-receptor complexes produces movement in cells developing polarity. Reversible accumulation of surface-bound Con A at the uropod occurring to a similar extent in untreated and colchicine-treated cells is partly due to membrane folding and partly to movement in the plane of the membrane.