A high-resolution shape fitting and simulation demonstrated equatorial cell surface softening during cytokinesis and its promotive role in cytokinesis.
Koyama H., Umeda T., Nakamura K, Higuchi T. and Kimura A. 
PLoS ONE 7(2): e31607 (2012). Published: February 16, 2012 
http://www.plosone.org/article/info%3Adoi%2F10.1371%2Fjournal.pone.0031607  

The Research Organization of Information and Systems (ROIS: http://www.rois.ac.jp/) promotes transdisciplinary researches integrating genetics, statistical mathematics, informatics and polar research. For this purpose, ROIS has established Transdisciplinary Research Integration Center (TRIC) to facilitate exchange and cooperation among the four national institutes. As a project of TRIC, Drs. Akatsuki Kimura (National Institute of Genetics; NIG) and Hiroshi Koyama (NIG, currently at National Institute for Basic Biology) collaborated with Drs. Tomoyuki Higuchi (The Institute of Statistical Mathematics; ISM), Kazuyuki Nakamura (ISM, currently at Meiji University), and Tamiki Umeda (Kobe University) and deviced a novel method to estimate cortical bending stiffness with high spatio-temporal resolution from in vivo cell shapes. Using the early Caenorhabditis elegans embryo as a model, the authors show that the stiffness of the equatorial cell surface is reduced during cytokinesis, whereas the stiffness of the polar cell surface remains stiff. Theoretical modeling showed that the equatorial reduction of stiffness was sufficient to generate a cleavage furrow even without the constriction force of the contractile ring. The authors conclude that stiffness is reduced around the equator. In addition, computational modeling suggests that proper regulation of stiffness could be sufficient for cleavage furrow ingression.  

Model of regulation of cell surface stiffness and its contribution to furrow ingression. In wild-type cells, cell surface stiffness around the furrow is locally reduced, which decreases the resistive force and promotes furrow ingression (left panel; blue arrow). Thus, the weaker contractile ring force (red arrow) becomes sufficient for furrow ingression. In the absence of ZEN-4, the cell surface is not softened and generates a larger resistive force against furrow ingression (right panel; blue arrow). (The figure is reprinted from Koyama et al., PLoS ONE 2012.)