Figure 5. The integration of various microtubule-regulated mechanisms underlies the self-organization and remodeling of cellular arrays.

(i) Top: Plant cortical arrays are reoriented by ~90° in response to blue light. Bottom: Zoomed-in view of region enclosed by black dashed box in top panel. Pre-existing microtubules (gray) of the longitudinal array generate new diagonal and transverse microtubules (brown) through successive branching microtubule nucleation events (magenta). New microtubules are amplified through severing (red scissors) at sites of nucleation and cross-overs (green dashed box), and polymerization of severed fragments. The disassembly of the original array completes the re-orientation process. (ii) Top: The spindle midzone, a cross-linked array of inter-digitating, anti-parallel microtubules is formed during anaphase to specify the site of cell cleavage and ensure error-free genome (green) propagation. Bottom: Zoomed-in view of region enclosed by black dashed box in top panel. Pre-existing microtubules (gray) serve as platforms to generate new parallel microtubules (brown) through branching microtubule nucleation (magenta). The location of the array at the center of the cell and its dimensions are specified by length-dependent microtubule depolymerization and generation of overlap length-dependent sliding and braking forces to produce stable overlaps.