MITOTIC FORCES CONTROL A CELL-CYCLE CHECKPOINT

EVERY time a cell divides, the chromosomes must be distributed accurat ely to the daughter cells. Errors in distribution arise if chromosomes are improperly attached to the mitotic spindle. Improper attachment i s detected by a cell-cycle checkpoint in many cells(1,2) and the compl etion of cell division is delayed, allowing time for error correction. How is an improperly attached chromosome detected? An absence of tens ion from mitotic forces is one possibility(3). Here we test this possi bility directly by applying tension to an improperly attached chromoso me with a micromanipulation needle, In the absence of tension, the ent ry into anaphase and the completion of mitosis was delayed by 5-6 hour s. When the misattached chromosome was placed under tension, however, the cell entered anaphase in 56 minutes, on average. Tension from mito tic forces or from a micromanipulator's needle evidently signals to th e checkpoint that all is in order and that cell division can proceed.