A force for holocentrics to reckon with

Holocentric chromosomes, like those of C. elegans, pose a dangerous attachment problem during mitosis. Their kinetochores are distributed along the length of the chromosomes and are thus easy targets for microtubules from both poles. If a single kinetochore is caught by two poles, the chromatid is held up at anaphase, causing segregation defects (as these merotelic attachments create tension, the mitotic checkpoint is not activated).

On page 991, Powers et al. uncover a chromosome-associated kinesin in worms that prevents persistent merotelic attachments. Although homologues of this plus-end microtubule motor, called KLP-19, are found in many systems, they may be especially critical in organisms with holocentric chromosomes.

Dividing worm cells that lacked KLP-19 had high rates of segregation errors due to merotelic attachments. Chromosomes congregated at the metaphase plate normally, but some then moved quickly...