PMC

Schematic for microtubule-dependent microtubule formation. The microtubule (tubulin dimer: white, green) can recruit and activate γ-tubulin ring complex (γ-TURC, blue), possibly via the augmin complex (grey).

Schematic for the “mini-spindle” assay. Optical trapping and TIRF (total internal reflection fluorescence) microscopy are combined to examine forces generated by kinesin-5 sliding two microtubules apart.

(A) Chromosomes (blue) generate signals to promote the formation of microtubules in their vicinity; (B) A spindle assembled around chromatinized DNA-beads added to Xenopus egg extracts. DNA: blue; tubulin: red. Scale bar, 5 μm.

The metaphase spindle. (A) Overlay shows tubulin (green) and DNA (blue) in a mammalian cell. The cell was fixed and processed for immunofluorescence. Scale bar, 5 μm; (B) Schematic highlights kinetochore (kMT), interpolar (ipMT), and astral microtubules. DNA: blue; kinetochore: red; tubulin: green; centrosome: black circle.

Metaphase spindle assembled in Xenopus egg extracts. (A) Overlay shows tubulin (red) and DNA (blue) in a metaphase spindle assembled around demembraned sperm DNA. Rhodamine-labeled tubulin was added to visualize microtubules, and Hoescht was used to stain DNA. Scale bar, 5 μm; (B) Schematic for the spindle assembled in Xenopus egg extracts. Tubulin: green, thicker lines indicate filament bundles; DNA: blue).

Schematics for how different motor proteins can crosslink and slide two microtubules apart. (A) A kinesin-5 homotetramer can walk towards the plus-end of each filament it crosslinks; (B) Kinesin-14 dimers crosslink microtubules via motor (circles) and non-motor (lines) domains. The motor domains can bind either filament and walk towards its minus-end; (C) Dynein dimers can walk towards the minus-ends of the microtubules. Each motor domain in the dimer may interact with a different filament; (D) Kinesin-12 homotetramers may slide parallel microtubules relative to each other by walking faster on one filament in the pair. Tubulin dimer: green, white; motor proteins: blue; V = velocity; in D, V1 is greater than V2; plus-end of the microtubule is also indicated (+).