  We investigate the final stage of cytokinesis in two types of amoeba,
pointing out the existence of biphasic furrow contraction. The first phase is
characterized by a constant contraction rate, is better studied, and seems
universal to a large extent. The second phase is more diverse. In Dictyostelium
discoideum the transition involves a change in the rate of contraction, and
occurs when the width of the cleavage furrow is comparable to the height of the
cell. In Entamoeba invadens the contractile ring carries the cell through the
first phase, but cannot complete the second stage of cytokinesis. As a result,
a cooperative mechanism has evolved in that organism, where a neighboring
amoeba performs directed motion towards the dividing cell, and physically
causes separation by means of extending a pseudopod. We expand here on a
previous report of this novel chemotactic signaling mechanism.
