Illustration of the formation of pseudocleavage furrow, the cell geometry and simplified interactions between the Par proteins.

<p>(A) Actomyosin initially starts to retract to the anterior of the cell and the pseudocleavage furrow begins to form; later the invagination becomes deeper and moves towards to anterior pole; the color represents the concentration of actomyosin (yellow to red refers to low to high concentration). In this and all subsequent figures, the posterior pole is at the bottom and the anterior pole is at the top. (B) A DIC image of a typical wild type <i>C. elegans</i> embryo at the end of the establishment phase, when the pseudocleavage furrow has reached the middle of the cell. (C) Schematic of a simplified network based on experimentally determined interactions. <i>A</i>_<i>m</i>: cortical anterior Par protein monomers, <i>A</i>_<i>sd</i>: cortical anterior singly bound dimers, <i>A</i>_<i>dd</i>: cortical anterior Par protein doubly bound dimers, <i>P</i>: cortical posterior Par proteins, <i>M</i>: cortical actomyosin. Solid arrowheads are cortical loss by conversion; double open arrowheads are cortical loss by regulated dissociation; light color species are phosphorylated forms. This figure is a reproduction of Figure 1 in [<a href="http://www.ploscompbiol.org/article/info:doi/10.1371/journal.pcbi.1006294#pcbi.1006294.ref021" target="_blank">21</a>]. (D) Illustration of the arrangement of actomyosin in a 3D view. The actomyosin proteins (gray curves on the membrane) are cross-linked away from pseudocleavage furrow and they are compressed in the furrow region due to the flow velocity gradient, leading to their alignment in the circumferential direction. The arrow indicates the inward force due to the actomyosin alignment.