| The mitotic spindle plays an essential role in chromosome segregation during cell division as it is the principle structure responsible for capturing, organizing, and separating chromosomes before cytoplasmic division creates two daughter cells from the mother cell. Spindle formation and proper function requires that microtubules (MTs) with opposite polarity overlap and interact. Previous computational simulations have demonstrated that these antiparallel interactions could be created by complexes combining plus and minus end directed motors. The resulting spindles, however, exhibit sparse antiparallel micro-tubule overlap with motor complexes linking only a nominal number of antiparallel microtubules. Here we investigate the role that various hypothesized mechanisms can have on spindle formation. First we consider the effects of spatial differences in the regulation of microtubule interactions on spindle morphology. We show that the spatial regulation of microtubule catastrophe parameters can lead to significantly better spindle morphology and spindles with greater antiparallel MT overlap. We next consider the effects of limiting the diffusion of motor complexes within the spindle region and find that it increases antiparallel microtubule interaction but does not improve MT distribution. We also demonstrate that antiparallel microtubule overlap can be increased by having new microtubules nucleated along the length of existing astral microtubules, but this increase negatively affects spindle morphology.;We also explore the effects of a lamin filament matrix---a mechanism whose role in spindle formation is less certain than that of molecular motors or spatial regulation. Based on biological observations it is believed that the lamin matrix could be interacting with molecular motors and stabilizing MTs within the spindle. We have included these lamin interactions into a continuum spindle assembly model to obtain realistic spindle morphologies. Through the continuum model we demonstrate translocation of lamin throughout the spindle via interactions with MTs after nuclear envelope breakdown, as well as improved spindle morphology through lamin based polymerization of MTs, though we did not find noticeable improvement by reducing diffusion of MTs via lamin. We also demonstrate improved spindle morphology with plus-end directed motor repulsion of the asters and improved MT density near the spindle equator through RanGTP and RanGDP gradients.;We also automatically detected and measured filaments within biological images of membrane structures. Statistically significant filament densities and branching densities comparisons were able to be made amongst the sample membrane data sets. |
