Fig. 5: Theoretical model of bundle formation.

a Schematic representation of the model. Kinetochores (gray) are equally spaced along the edge of the spindle midplane. Microtubules (green) and crosslinkers (white) are initially uniformly distributed and gather into bundles over time. b Steady-state microtubule density, \({\rho }_{{{{{{\rm{f}}}}}}}\), for 4 values of the kinetochore-microtubule attraction, \(\alpha\), as indicated. Other parameters are: \(\psi \,=\,10000\,\mu {m}^{-1}\), \(d\,=\,2\,\mu m\), \(\kappa \,=\,10\,\mu {m}^{3}\), \(w\,=\,1\,\mu {m}^{3}\). The kinetochores are positioned at \(x\,=\,\pm d\). c Steady-state microtubule density, \({\rho }_{{{{{{\rm{f}}}}}}}\), for 3 values of the crosslinker density, \(\psi\), as indicated; \(\alpha \,=\,20\,\mu {m}^{2}\), \(d\,=\,1\,\mu m\),\(\,\kappa \,=\,5\,\mu {m}^{3}\), \(w\,=\,0.01\,\mu {m}^{3}.\) d Spindle in a HeLa-TDS cell with overexpressed PRC1. Top: microtubules (SiR-tubulin, green) and DNA (Hoechst 33342, magenta), bottom: PRC1-mCherry (white). Scale bar, 1 µm. Similar observations were made in more than 10 cells from 3 independent experiments. e Steady-state microtubule density, \({\rho }_{{{{{{\rm{f}}}}}}}\), for 3 values of the distance between kinetochores, 2\(d\), as indicated; \(\alpha \,=\,10\,\mu {m}^{2}\), \(\psi \,=\,10000\,\mu {m}^{-1}\), \(\kappa \,=\,10\,\mu {m}^{3}\), \(w\,=\,1\,\mu {m}^{3}\). Other parameters are kept fixed at \(\zeta \,=\,0.016\,\mu {m}^{2}\), \({\bar{\omega }}_{{{{{{\rm{on}}}}}}}\,=\,0.8\,\mu {m}^{-1}{s}^{-1}\), \({\omega }_{{{{{{\rm{off}}}}}}}\,=\,0.02{s}^{-1}\), \({M}_{\rho }\,=\,0.02\,\mu m\bullet {s}^{-1}\). Determination of the parameters is described in Methods.