The spindle, or spindle apparatus is an structure that segregates chromosomes during cell division, and is formed by Microtubules, Molecular motors, and hundreds of other proteins. The spindle self-organizes during division process.
(https://en.wikipedia.org/wiki/Spindle_apparatus)
For the frog Xenopus laevis, spindles are on average ~45 microns long, and ~30 microns wide. Microtubules in these spindles have an average length of ~7 microns (ref) and are at a density of ~50-100 microtubules/m^2, implying that there are ~100,000 (ref 1, ref 2). Microtubules are polar polymers whose minus ends are relatively static and whose plus ends polymerize at a speed of ~10-20 m/min (ref). There is no appreciable rate of rescues in these spindles ? (ref), and the half-life of these microtubules is ~16s, much shorter than the typical lifetime of a spindle – which can exist for several hours. Microtubules in the spindle interact with each other via motrs and cross-linkers, and continuously slide toward the poles at a rate of ~2.5 m/min (ref 1, ref 2)
Nucleation and Transport Organize Microtubules in Metaphase Spindles
Microtubule Plus-End Dynamics in Xenopus Egg Extract Spindles
The kinesin Eg5 drives poleward microtubule flux in Xenopus laevis egg extract spindles. Although mitotic and meiotic spindles maintain a steady-state length during metaphase, their antiparallel microtubules slide toward spindle poles at a constant rate. This "poleward flux" of microtubules occurs in many organisms and may provide part of the force for chromosome segregation. [...] Our results suggest that ensembles of nonprocessive Eg5 motors drive flux in metaphase Xenopus extract spindles.