Microtubules interpolar

Spindle microtubules generally lie parallel to one another and to the interpolar axis, but some microtubules crossing others at any angle are found, especially early in prometaphase (e.g., Bajer, 1968c Bajer and Mole-Bajer, 1969). The parallel arrangement of microtubules usually breaks down near the poles. This is especially evident in cells with centrioles, where the spindle microtubules terminate close to, but not at, the centrioles, amid a field of microtubules running in every direction (reviewed by de Harven, 1968 Robbins et al., 1968). Interestingly, intranuclear spindles of protozoa show parallel microtubules all the way to the pole (Jenkins, 1967 Tucker, 1967). 

Other the rest terminate in the region of overlap. These features are established unequivocally before the association of chromosomes with the spindle. Interpolar and chromosomal microtubules begin to form at separate times and in separate places, removing much ambiguity at least for the initial stages (see other examples of the central... 

Fig. 3. Electron micrograph of metaphase in the micronucieus of the ciliate Blepharisma sp. showing both chromosomal microtubules (e.g., arrows at left) and interpolar microtubules (e.g., arrow at right). Note the fine fibrous material around the microtubules. X50,000. (From Jenkins. 1967. J. CeU. Biol., 34 463-481.)...

Fig. 8. Diagrammatic representation of a hypothesis (McIntosh et al., 1969) of mitotic force production based upon sliding of polarized interpolar ( Ip ) and chromosomal ("Ch") microtubules caused by cross-bridges (short, diagonal arrows) between them. A., The basic motile unit. B, Metaphase, showing two sister chromatids linked together (bold horizontal bars) and a minimal number of microtubules. C, and D, Two stages in anaphase after dissolution of the chromatid linkages. Details In the text. (Adapted from McIntosh et al. 1969. Nature (London), 224 659-663.)...

Sharp D.J., McDonald K.L., Brown H.M., Matthies H.J., Walczak C., Vale R.D., Mitchison T.J., and Scholey J.M. 1999. The bipolar kinesin, KLP61F, associates with interpolar microtubule bundles within mitotic spindles of Drosophila early embryos. J. Cell Biol. 144 125-138. 

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