Regulators of chromosome movement and the mitotic spindle checkpoint

Abstract

Balanced chromosome segregation requires coordination of chromosome movement on the spindle with regulation of cell cycle progression through mitosis. Initial attachments of chromosomes to spindle microtubules often appear due to kinetochores of chromosomes attaching and moving on the lateral surfaces of microtubules. These mature into end‐on microtubule attachments. Microtubule attachment and mechanical tension induced by bipolar attachment of sister kinetochores serve to bring chromosomes to alignment at the metaphase plate and simultaneously silence the spindle checkpoint. We have found that inhibition of the Ndc80 complex at kinetochores by antibody microinjection results in loss of metaphase alignment. Inhibition of the Ndc80 complex also results in abrogation of the mitotic spindle checkpoint. Thus in such cells, chromatids separate but completely fail to undergo anaphase movements. We hypothesize that the residual chromosome movements seen in prometaphase cells lacking Ndc80 function are due to dynein/dynactin at kinetochores modulating lateral attachments of kinetochores to spindle microtubules. We are studying chromosome movements on monopolar spindles induced with the drug monastrol to dissect the mechanisms that mediate chromosome movement and checkpoint protein dynamics in mitosis.