Active sliding between cytoplasmic microtubules

Abstract

Microtubules are versatile cellular polymers that play a role in cell shape determination and mediate various motile processes such as ciliary and flagellar bending, chromosome movements and organelle transport¹. That a sliding microtubule mechanism can generate force has been demonstrated in highly ordered structures such as axonemes^2,3, and microtubule-based force generation almost certainly contributes to the function of mitotic and meiotic spindles^4,5. Most cytoplasmic microtubule arrays, however, do not exhibit the structural regularity of axonemes and some spindles, and often appear disorganized. Yet many cellular activities (such as shape changes during morphogenesis^6–9, axonal extension^10,11 and spindle assembly) involve highly coordinated microtubule behaviour and possibly require force generated by an intermi-crotubule sliding mechanism, or perhaps use sliding to move microtubules rapidly into a protrusion for stabilization¹². Here we show that active sliding between cytoplasmic microtubules can occur in microtubule bundles of the amoeba Reticulomyxa. A force-producing mechanism of this sort could be used by this organism to facilitate the extension of cell processes and to generate the dynamic movements of the cytoplasmic network.