CENP-E is essential for reliable bioriented spindle attachment, but chromosome alignment can be achieved via redundant mechanisms in mammalian cells

CENP-E is a kinesin-like protein that when depleted from mammalian kinetoch ores leads to mitotic arrest with a mixture of aligned and unaligned chromo somes. In the present study, we used immunofluorescence, video, and electro n microscopy to demonstrate that depletion of CENP-E from kinetochores via antibody microinjection reduces kinetochore microtubule binding by 23% at a ligned chromosomes, and severely reduces microtubule binding at unaligned c hromosomes. Disruption of CENP-E function also reduces tension across the c entromere, increases the incidence of spindle pole fragmentation, and resul ts in monooriented chromosomes approaching abnormally dose to the spindle p ole. Nevertheless, chromosomes show typical patterns of congression, fast p oleward motion, and oscillatory motions. Furthermore, kinetochores of align ed and unaligned chromosomes exhibit normal patterns of checkpoint protein localization. These data are explained by a model in which redundant mechan isms enable kinetochore microtubule binding and checkpoint monitoring in th e absence of CENP-E at kinetochores, but where reduced microtubule-binding efficiency, exacerbated by poor positioning at the spindle poles, results i n chronically monooriented chromosomes and mitotic arrest. Chromosome posit ion within the spindle appears to be a critical determinant of CENP-E funct ion at kinetochores.