Rho-kinase controls cell shape changes during cytokinesis.
BACKGROUND
Animal cell cytokinesis is characterized by a sequence of dramatic cortical rearrangements. How these are coordinated and coupled with mitosis is largely unknown. To explore the initiation of cytokinesis, we focused on the earliest cell shape change, cell elongation, which occurs during anaphase B and prior to cytokinetic furrowing.


RESULTS
Using RNAi and live video microscopy in Drosophila S2 cells, we implicate Rho-kinase (Rok) and myosin II in anaphase cell elongation. rok RNAi decreased equatorial myosin II recruitment, prevented cell elongation, and caused a remarkable spindle defect where the spindle poles collided with an unyielding cell cortex and the interpolar microtubules buckled outward as they continued to extend. Disruption of the actin cytoskeleton with Latrunculin A, which abolishes cortical rigidity, suppressed the spindle defect. rok RNAi also affected furrowing, which was delayed and slowed, sometimes distorted, and in severe cases blocked altogether. Codepletion of the myosin binding subunit (Mbs) of myosin phosphatase, an antagonist of myosin II activation, only partially suppressed the cell-elongation defect and the furrowing delay, but prevented cytokinesis failures induced by prolonged rok RNAi. The marked sensitivity of cell elongation to Rok depletion was highlighted by RNAi to other genes in the Rho pathway, such as pebble, racGAP50C, and diaphanous, which had profound effects on furrowing but lesser effects on elongation.


CONCLUSIONS
We show that cortical changes underlying cell elongation are more sensitive to depletion of Rok and myosin II, in comparison to other regulators of cytokinesis, and suggest that a distinct regulatory pathway promotes cell elongation.
Department of Biochemistry and Biophysics, University of California, San Francisco, San Francisco, California 94143-2200, USA.
Gilles R X
GR
Hickson
Arnaud
A
Echard
Patrick H
PH
O'Farrell
D000705:Anaphase / Q000502:physiology; D000818:Animals; D002460:Cell Line; D048430:Cell Shape / Q000502:physiology*; D048749:Cytokinesis / Q000502:physiology*; D004330:Drosophila; D047908:Intracellular Signaling Peptides and Proteins; D018715:Microscopy, Video; D024507:Nonmuscle Myosin Type IIA / Q000502:physiology; D017346:Protein Serine-Threonine Kinases / Q000502:physiology*; D054460:rho-Associated Kinases
D047908:Intracellular Signaling Peptides and Proteins; D017346:Protein Serine-Threonine Kinases; D054460:rho-Associated Kinases; D024507:Nonmuscle Myosin Type IIA