A force-balance model for centrosome positioning and spindle elongation during Interphase and Anaphase B

A computational model in one dimension is proposed to position a single centrosome using astral microtubules (MTs) interacting with the cell cortex. The mechanism exploits mutually antagonistic pulling and pushing forces arising from the astral MTs9 binding to cortical dynein motors in the actin-rich cell cortex and their buckling while growing against the cell cortex, respectively. The underlying mechanism of astral MTs is also extended to account for the elongation and positioning of the bipolar spindle during mitotic anaphase B. The model for bipolar spindle involves both IPMTs and astral MTs, can predict its elongation and positioning under various circumstances. The model reveals that the bipolar spindle elongation, weakened by decreasing overlap between the antiparallel interpolar microtubules (IPMTs) in the spindle mid-zone, is recovered by the astral MTs.