Cytokinesis in HeLa: Post-telophase delay and microtubule-associated motility

Summary

Phase-contrast microcinematography of cultured HeLa cells reveals that cell separation is considerably delayed after telophase. During this period of delay, the daughter cells lose their rounded morphology and become flattened against the substrate, as occurs in interphase. After two or more hours, the cells again become rounded while the thin intercellular bridge connecting them begins to elongate. This active elongation involves the migration of thickenings (“waves”) along the bridge from the midbody at its center toward either cell. Later, waves occur only on one side of the midbody as this half of the bridge alone continues to elongate. The arrival of waves at the cells is accompanied not only by discrete increases of length in that half of the bridge, but also by blebbing activity in that cell. Rupture of the bridge finally occurs just adjacent to the cell receiving these latter waves.

Electron microscopic examination of cells in post-telophase delay has demonstrated a bundle of microtubules passing into either cell from the midbody in the center of the intercellular bridge. These microtubules are of constant length during bridge elongation; the cells are simply forced distally along the surface of the microtubule bundle. The waves themselves are found to contain microtubules just as straight as those in the rest of the bridge, so it is concluded that the force apparently generated here consists of the longitudinal translation of material along the surfaces of the rigid microtubules. It is pointed out that these forces may operate in the earlier phases of mitosis and in other systems of microtubule-associated motility. We also discuss the possible roles of post-telophase delay and of active bridge elongation in the organization of normal tissues.