Cell cycle regulation of central spindle assembly

Abstract

The bipolar mitotic spindle is responsible for segregating sister chromatids at anaphase. Microtubule motor proteins generate spindle bipolarity and enable the spindle to perform mechanical work. A major change in spindle architecture occurs at anaphase onset when central spindle assembly begins. This structure regulates the initiation of cytokinesis and is essential for its completion. Central spindle assembly requires the centralspindlin complex composed of the Caenorhabditis elegans ZEN-4 (mammalian orthologue MKLP1) kinesin-like protein and the Rho family GAP CYK-4 (MgcRacGAP). Here we describe a regulatory mechanism that controls the timing of central spindle assembly. The mitotic kinase Cdk1/cyclin B phosphorylates the motor domain of ZEN-4 on a conserved site within a basic amino-terminal extension characteristic of the MKLP1 subfamily. Phosphorylation by Cdk1 diminishes the motor activity of ZEN-4 by reducing its affinity for microtubules. Preventing Cdk1 phosphorylation of ZEN-4/MKLP1 causes enhanced metaphase spindle localization and defects in chromosome segregation. Thus, phosphoregulation of the motor domain of MKLP1 kinesin ensures that central spindle assembly occurs at the appropriate time in the cell cycle and maintains genomic stability.

Hippo signalling in the G2/M cell cycle phase: Lessons learned from the yeast MEN and SIN pathways

“…However, this does not mean that Cdc14 has no role to play in mitosis, since overexpression of Cdc14 leads to cytokinesis defects in mammalian cells [18]. In addition, Cdc14 can be detected at the spindle midzone and midbody in animal cells [97][98][99][100][101]. These reports suggest that mammalian Cdc14 phosphatases are not essential for mitotic progression, although they can have negative effects on mitotic processes upon overexpression.…”

Cytokinesis microtubule organisers at a glance

“…In mitotic cells, the majority of MKLP1 and CYK4 are in the centralspindlin complex and there is no clear evidence for the presence of free components. The motor domain of MKLP1 possesses the microtubule plus-enddirected motor activity (Hizlan et al, 2006;Mishima et al, 2004;Nislow et al, 1992), which is essential for proper microtubule bundle formation and deposition of the midbody matrix (Matuliene and Kuriyama, 2002). The neck region of MKLP1, which links the motor domain to a relatively short coiledcoil stalk domain, is unusually long and contains the binding site for CYK4 (Mishima et al, 2002;PavicicKaltenbrunner et al, 2007;Somers and Saint, 2003).…”

“…The atomic structure of centralspindlin is not known, except for the GAP domain of CYK4, whose target Rho-family GTPase is under debate (Canman et al, 2008;JantschPlunger et al, 2000;Miller and Bement, 2009;Yamada et al, 2006;Zavortink et al, 2005). Similar to PRC1, the interaction of centralspindlin with microtubules is suppressed by CDK1 phosphorylation before anaphase onset (Goshima and Vale, 2005;Mishima et al, 2004). The heterotetrameric centralspindlin forms higher-order clusters in a manner that is regulated by Aurora B kinase and 14-3-3 proteins Hutterer et al, 2009).…”

Cell cycle control of spindle elongation

“…7,27,60,[79][80][81] Accordingly, several proteins involved in spindle assembly and regulation of MT dynamics have been uncovered as targets of this regulatory scheme. 60,69,[82][83][84] Whereas the majority of these substrates have only been identified in a subset of organisms, phosphorylation of the central midzone marker Ase1/PRC1 by Cdk1 in metaphase and reversal of these modifications in anaphase seems to be conserved among all model systems. 72,[85][86][87][88] …”