Pronuclear migration induced by polymerization forces
No Sliding Model.
This is a direct simulation of the pronuclear migration stage in cell division. In this particular simulation the pronuclear complex, shown here as the red sphere, is positioned by the elastic deformation of growing microtubules on the cortex boundary. The simulations include 600 microtubules (MTs) and includes hydrodynamic interactions of MTs with the cytoplasmic fluid and the boundaries. The colors denote the compressive tension on the MTs.
In this particular implementation, we assume that once the MTs reach within a distance from the boundary they get trapped (their position remains fixed) on the boundary until they start to shrink due to dynamic instability. This model seems to properly center and align the pronuclear complex.
Free Sliding Model:
This video shows the dynamic simulation of the migration of the pronuclear complex through repulsive polymerization forces applied from the cell periphery to the growing microtubules (MTs) reaching the boundaries. In this model, we assume that the polymerization force is applied in the direction normal to the surface. As a result as the MTs bend less and less force is applied from the boundary on the MTs. In the limit of MTs being aligned with the boundary they can grow or slide freely. In this model, the pronuclear complex (PNC) does properly center; yet the alignment of the PNC is not observed.
Sedimentation of a cloud of flexible fibers
A suspension of 1024 flexible fibers are uniformly distributed within a spherical volume. The fibers sediment under the gravitational forces. The spherical shape of this "cloud" of particles undergoes complex changes and eventually forms a torus-like structure.