Mechanical and Geometrical Constraints Control Kinesin-Based Microtubule Guidance

Abstract

Proper organization of microtubule networks depends on microtubule-associated proteins and motors that use different spatial cues to guide microtubule growth [1-3]. For example, it has been proposed that the uniform minus-end-out microtubule organization in dendrites of Drosophila neurons is maintained by steering of polymerizing microtubules along the stable ones by kinesin-2 motors bound to growing microtubule plus ends [4]. To explore the mechanics of kinesin-guided microtubule growth, we reconstituted this process in vitro. In the presence of microtubule plus-end tracking EB proteins, a constitutively active kinesin linked to the EB-interacting motif SxIP effectively guided polymerizing microtubules along other microtubules both in cells and in vitro. Experiments combined with modeling revealed that at angles larger than 90°, guidance efficiency is determined by the force needed for microtubule bending. At angles smaller than 90°, guidance requires microtubule growth, and guidance efficiency depends on the ability of kinesins to maintain contact between the two microtubules despite the geometrical constraints imposed by microtubule length and growth rate. Our findings provide a conceptual framework for understanding microtubule guidance during the generation of different types of microtubule arrays.

Kinesin-12 motors cooperate to suppress microtubule catastrophes and drive the formation of parallel microtubule bundles

“…3D). However, a recent description of a similar microtubule transport process mediated by artificial adducts of kinesins and plus-end-tracking proteins showed that the maximal transport velocities are affected by the intersection geometry (19,20). We therefore checked whether the length of the cargo microtubule (the force that is needed to bend a microtubule decreases with its length) or the angle at which cargo and substrate microtubule meet has any influence on the maximal transport velocity in our setup.…”

“…After an intersection has been established, processive hKif15 motors accumulate at these intersections either as a result of motors walking up to an intersection or by plus-end-tracking motors that already had been deposited there during formation of the intersection. In case of an incomplete "end-on" intersection, hKif15-driven transport is reminiscent of microtubule steering/guidance described for artificial adducts of plus-end-binding proteins and kinesins (19,20). However, hKif15 integrates all essential activities-plus-end tracking, cross-linking, and processive motility-into a single bivalent motor that can operate as an autarkic functional unit.…”

Coordinating Neuronal Actin–Microtubule Dynamics

“…In neurons, dynein has been proposed to target microtubules to actin networks at the cell edge either through the formation of a lissencephaly 1 (Lis1)-dynactindynein +TIP complex or through interaction with the cell-surface receptor neuronal cell adhesion molecule (NCAM) [143,144] ( Figure 3C). Analogous to the zippering of microtubules along actin filaments (discussed in the +TIPs section), microtubules can also engage and polymerise along other microtubules, guided by motor-protein-containing +TIP complexes such as EB1-APC-kinesin2 [145][146][147]. This complex is required for the persistence of minus-end-out (i.e.…”

Building the Neuronal Microtubule Cytoskeleton

“…Work in Drosophila proposed that growing MTs approaching a branch are guided toward the plus ends of pre-existing MTs by a Kinesin-2 that interacts with the growing plus end through EB1 and APC ( Figure 3J) (Mattie et al, 2010). Subsequent in vitro reconstitution experiments have demonstrated that kinesins interacting with dynamic plus ends through EB proteins can indeed establish MT guidance Doodhi et al, 2014).…”