Cell Biology

Size Matters

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Science  28 Aug 2009:
Vol. 325, Issue 5944, pp. 1048
DOI: 10.1126/science.325_1048c
CREDIT: DINARINA ET AL., CELL 138, 502 (2009)

The mitotic spindle, which pulls apart the duplicated chromosomes during cell division in animal and plant cells, is composed of microtubules that have been found to self-assemble in the presence of chromosomes. Dinarina et al. have developed a cellfree system in order to monitor the effects of chromosome size and shape on spindle morphology. Microscopic chromatin-coated beads were arrayed on a glass slide to which cytoplasmic extracts from Xenopus laevis were applied, which made it feasible to look at many individual spindles assembling simultaneously. When chromatin (blue) was deposited as circular spots 15 µm in diameter, typical bipolar spindles (red) were observed, and larger spots tended to produce spindles with additional poles. In contrast, for chromatin patterned in a chromosome-like rectangle with dimensions of 6 x 18 µm, a typical bipolar spindle orthogonal to the long axis of the chromosome was seen. Longer chromatin arrangements generated multipolar, disorganized spindles, which also generally crossed the long axis of the chromosome, and thicker arrangements generated multiple half-spindles along one side of the patch of chromatin. Thus, the size and shape of chromosomes can define microtubule spindle shape and orientation.

Cell 138, 502 (2009).

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