Parameters That Specify the Timing of Cytokinesis

Abstract

One model for the timing of cytokinesis is based on findings that p34cdc2 can phosphorylate myosin regulatory light chain (LC20) on inhibitory sites (serines 1 and 2) in vitro (Satterwhite, L.L., M.H. Lohka, K.L. Wilson, T.Y. Scherson, L.J. Cisek, J.L. Corden, and T.D. Pollard. 1992. J. Cell Biol. 118:595–605), and this inhibition is proposed to delay cytokinesis until p34cdc2 activity falls at anaphase. We have characterized previously several kinase activities associated with the isolated cortical cytoskeleton of dividing sea urchin embryos (Walker, G.R., C.B. Shuster, and D.R. Burgess. 1997. J. Cell Sci. 110:1373–1386). Among these kinases and substrates is p34cdc2 and LC20. In comparison with whole cell activity, cortical H1 kinase activity is delayed, with maximum levels in cortices prepared from late anaphase/telophase embryos. To determine whether cortical-associated p34cdc2 influences cortical myosin II activity during cytokinesis, we labeled eggs in vivo with [32P]orthophosphate, prepared cortices, and mapped LC20 phosphorylation through the first cell division. We found no evidence of serine 1,2 phosphorylation at any time during mitosis on LC20 from cortically associated myosin. Instead, we observed a sharp rise in serine 19 phosphorylation during anaphase and telophase, consistent with an activating phosphorylation by myosin light chain kinase. However, serine 1,2 phosphorylation was detected on light chains from detergent-soluble myosin II. Furthermore, cells arrested in mitosis by microinjection of nondegradable cyclin B could be induced to form cleavage furrows if the spindle poles were physically placed in close proximity to the cortex. These results suggest that factors independent of myosin II inactivation, such as the delivery of the cleavage stimulus to the cortex, determine the timing of cytokinesis.

A Global, Myosin Light Chain Kinase-dependent Increase in Myosin II Contractility Accompanies the Metaphase–Anaphase Transition in Sea Urchin Eggs

“…This stands in contrast to earlier models for the timing of cytokinesis where myosin II activity was thought to be dependent on complete inactivation of cyclindependent kinase . However, previous manipulation studies in sea urchin eggs (Shuster and Burgess, 1999) as well as in tissue culture cells (Rosenblatt et al, 2004) argue that myosin II activity may not be significantly suppressed during mitosis. Furthermore, mobilization of calcium early in mitosis resulted in a cortical contractile response (Figure 10), providing yet further evidence that myosin II is capable of responding to contractile signals in the presence of elevated cyclin-dependent kinase (CDK)1 activity.…”

“…Previous mapping of MRLC phosphorylation in dividing sea urchin eggs revealed an increase in cortical Ser19 phosphorylation during anaphase but detected little Ser19 phosphorylation during metaphase (Shuster and Burgess, 1999). To examine myosin activation in vivo, fertilized eggs were fixed and processed for microtubule and phospho-Ser19 MRLC localization ( Figure 3) by using an antibody previously demonstrated to react with phosphorylated sea urchin myosin regulatory light chain (Stack et al, 2006) aphase or cytokinesis, where light chain phosphorylation was confined to the cleavage plane (Figure 3, G-L).…”

Cytokinetic actomyosin ring formation and septation in fission yeast are dependent on the full recruitment of the polo-like kinase Plo1 to the spindle pole body and a functional spindle assembly checkpoint

“…As its name implies, the constriction of the CAR is based on the sliding interaction of actin filaments powered by the motor activity of a type II myosin (Schroeder, 1973). Numerous other proteins are required for ring assembly and contraction and to link the CAR to the cell membrane, allowing actin filament sliding to constrict the cell surface in the space vacated by the retreating chromosomes (reviewed in Rappaport, 1996;Shuster and Burgess, 1999;Glotzer, 2001).…”

RhoA GTPase controls cytokinesis and programmed necrosis of hematopoietic progenitors

“…The nuclei were well separated but not condensed, suggesting that cytokinesis, rather than karyokine sis, was impaired. Indeed, a closer examination of 4N LK cells found a major accumulation of anaphaselike cells, which usu ally coincided with cytokinesis (Shuster and Burgess, 1999), whereas the frequency of metaphase cells was not significantly altered ( Fig. 6 D), also suggesting a deficiency in later mitotic phases.…”