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. Author manuscript; available in PMC: 2013 May 1.
Published in final edited form as: Trends Cell Biol. 2012 Apr 3;22(5):241–249. doi: 10.1016/j.tcb.2012.02.007

Figure 2. Models of centrosomal and acentrosomal spindle assembly.

Figure 2

Centrosomal spindles assemble in somatic cells, in spermatocytes and in echinoderm oocytes. Microtubules nucleated from the centrosomes (yellow) oscillate between phases of growth and shrinkage `searching' for chromosomes. End-on contact with a kinetochore results in `capture' of a chromosome and stabilization of the microtubule to form a kinetochore fiber (orange).

In mouse oocytes, multiple MTOCs (yellow) assemble microtubule aster-like structures in the vicinity of chromosomes that subsequently are organized into a bipolar spindle. Kinetochore fibers are periodically destabilized and re-established to maintain oscillating chromosomes at the spindle equator during the extended prometaphase.

In Drosophila oocytes, microtubule asters first assemble at NEBD away from chromosomes in the absence of discrete PCM-containing MTOCs. These acentrosomal asters are subsequently remodeled and incorporated into the forming spindle, which is assembled by sorting and focusing of microtubule (−)-ends at the spindle poles.

In cell-free Xenopus extracts, microtubules are nucleated in the vicinity of chromatin-coated beads in random orientation and are subsequently sorted into an antiparallel microtubule array that surrounds chromosomes. Microtubule (−)-ends are focused away from chromosomes to form the spindle poles.