Collective cargo hauling by a bundle of parallel microtubules: bi-directional motion caused by load-dependent polymerization and depolymerization

摘要

A microtubule (MT) is a hollow tube of approximately 25 nm diameter. The twoends of the tube are dissimilar and are designated as `plus' and `minus' ends.Motivated by the collective push and pull exerted by a bundle of MTs duringchromosome segregation in a living cell, we have developed here a muchsimplified theoretical model of a bundle of parallel dynamic MTs. The plus-endof all the MTs in the bundle are permanently attached to a movable `wall' by adevice whose detailed structure is not treated explicitly in our model. Theonly requirement is that the device allows polymerization and depolymerizationof each MT at the plus-end. In spite of the absence of external force anddirect lateral interactions between the MTs, the group of polymerizing MTsattached to the wall create a load force against the group of depolymerizingMTs and vice-versa; the load against a group is shared equally by the membersof that group. Such indirect interactions among the MTs gives rise to the richvariety of possible states of collective dynamics that we have identified bycomputer simulations of the model in different parameter regimes. Thebi-directional motion of the cargo, caused by the load-dependence of thepolymerization kinetics, is a "proof-of-principle" that the bi-directionalmotion of chromosomes before cell division does not necessarily need activeparticipation of motor proteins.