Mechanisms for microtubule guidance and bundling. Green: GFP-AtEB1 (in A-H and N) and GFP-MAP4 (in I-M). Red: YFP-MAP4 (in C, E-G and N) and YFP-CLIP170 (in D). (A) 3-D maximum projection of interphase BY-2 cell, highlighting punctuate GFP-AtEB1 labeling in the cortex. (B) In interphase cells, GFP-AtEB1 comets at the cortex move in the same or opposite direction on the same track (arrowheads), and sometimes together (arrow) (See 1: Movie 1). (C) In co-transformed cells, GFP-EB1 labels the growing ends of microtubules labeled by YFP-MAP4 (See 2: Movie 2). (D) Co-localization of GFP-AtEB1 and YFP-CLIP170 on growing microtubule plus ends (See 3: Movie 3). (E) GFP-AtEB1 labeled growing microtubule changing from one microtubule track (labeled with YFP-MAP4) to another.  Growth of two separate unbundled microtubules (arrowheads) transiently meeting (arrow) and afterwards separating without inducing catastrophe. (G) Microtubules growing in opposite directions on the same track with similar speed (arrowheads) meet (arrow) and continue growing in opposite directions without inducing catastrophe. (H) Microtubule nucleation and growth (arrowheads) on an already existing microtubule (arrow). (I) Situation where attachment of a microtubule plus end (yellow arrowhead) to an existing microtubule induces a translocation of the minus end (red arrowhead) from one microtubule to another. (J) Microtubule plus end (yellow arrowhead) growing towards an existing microtubule, followed by guided growth in a new direction, causes bending at the point of previous attachment (red arrowhead). (K) Treadmilling microtubule (red arrowhead) with its plus end (red arrow) and minus end (yellow arrowhead) moving in the same direction (yellow arrowheads and red arrows) initiates bundling by bridging two other separate preexisting microtubules. (L) Long microtubule growing (arrowhead) and interacting with an existing microtubule induces reorientation of growth and bending, resulting in bundling with a shorter growing microtubule. (M) Depolymerization of one microtubule partially associated with a bundle (yellow arrowhead) causes bending of the remaining structure (red arrowhead). (N) Microtubule minus end detachment and subsequent movement (arrowheads) induces loss of GFP-AtEB1 from its plus end (yellow arrows); it recovers GFP-AtEB1 labeling and plus end growth once its minus end acquires new support on another polymer (arrowhead). Note that the same microtubule bends (red arrow) when its minus end is fixed and the plus end (yellow arrow) hits another microtubule. Time is indicated in seconds and bars represent 5 μm in A-D, 3 μm in K-M, 2 μm in E, I, J and 1 μm in F-H, N.
Dhonukshe et al. BMC Biology 2005 3:11 doi:10.1186/1741-7007-3-11