Cytokinesis is a complex process that involves dynamic cortical rearrangement. Our recent time-lapse recordings of the mouse egg unexpectedly revealed a high motility of the second polar body (2pb). Experiments to address its underlying mechanism show that neither mechanical compression by the zona pellucida nor the connection via the mid-body is required for the 2pb movement. Time-lapse recordings establish that the 2pb moves together with the cell membrane. These recordings, in which cell surface proteins are labeled with fluorescent latex-microbeads or monovalent antibodies against whole mouse proteins, indicate that the majority of the surface proteins dynamically accumulate in the cleavage furrow at every cell division. Comparable dynamics of the cell surface proteins, and specifically of E-cadherin, are also observed in cultured epithelial cells. The surface protein dynamics are closely correlated with, and dependent on, those of the underlying cortical actin. The cortical actin network may form a scaffold for membrane proteins and thereby transfer them during contractile ring formation toward the cleavage furrow. Immobilization of surface proteins by tetravalent lectin-mediated crosslinking results in the failure of cleavage, demonstrating that the observed protein dynamics are essential for cytokinesis. We propose that dynamic rearrangement of the cell surface proteins is a common feature of cytokinesis, playing a key role in modifying the mechanical properties of the cell membrane during cortical ingression.
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