Inside and Outside the Beltway

Abstract

CELL BIOLOGY Microtubules form the mitotic spindle, which is the scaffold on which chromosomes are separated. Inoue et al. wanted to understand what microtubules might do after the partitioning of the chromosomes is complete; in the final stage of cell division, cytokinesis, the two daughter cells are physically separated from one another. Looking at primary spermatocytes from Drosophila melanogaster with time-lapse microscopy, they find that at the onset of cytokinesis the central spindle has two populations of microtubules—some localized to the interior of the central spindle and others extending toward the periphery—which are affected differentially in the presence of a mutant form of the microtubule-associated protein Orbit (aka Mast or CLASP). Normally, Orbit localizes to interior rather than peripheral central spindle microtubules, but in hypomorphic orbit mutants these interior microtubules become less stable. The remaining peripheral microtubules can still probe the cell cortex, where they help to initiate the cleavage furrow. However, some of the other components involved in cytokinesis fail to assemble properly, and ultimately the furrow regresses, yielding multinucleate cells. — SMH J. Cell Biol. 166 , 49 (2004).