Merotelic Kinetochore Orientation Is a Major Mechanism of Aneuploidy in Mitotic Mammalian Tissue Cells

Abstract

Abstract. In mitotic cells, an error in chromosome segregation occurs when a chromosome is left near the spindle equator after anaphase onset (lagging chromosome). In PtK1 cells, we found 1.16% of untreated anaphase cells exhibiting lagging chromosomes at the spindle equator, and this percentage was enhanced to 17.55% after a mitotic block with 2 M nocodazole. A lagging chromosome seen during anaphase in control or nocodazole-treated cells was found by confocal immunofluorescence microscopy to be a single chromatid with its kinetochore attached to kinetochore microtubule bundles extending toward opposite poles. This merotelic orientation was verified by electron microscopy. The single kinetochores of lagging chromosomes in anaphase were stretched laterally (1.2-5.6-fold) in the directions of their kinetochore microtubules, indicating that they were not able to achieve anaphase poleward movement because of pulling forces toward opposite poles. They also had inactivated mitotic spindle checkpoint activities since they did not label with either Mad2 or 3F3/2 antibodies. Thus, for mammalian cultured cells, kinetochore merotelic orientation is a major mechanism of aneuploidy not detected by the mitotic spindle checkpoint. The expanded and curved crescent morphology exhibited by kinetochores during nocodazole treatment may promote the high incidence of kinetochore merotelic orientation that occurs after nocodazole washout.

Histone Hyperacetylation in Mitosis Prevents Sister Chromatid Separation and Produces Chromosome Segregation Defects

“…Previous studies in PtK1 and human cells have demonstrated that lagging chromosomes at anaphase are single sisters that cannot migrate because their kinetochore is attached to microtubules coming from opposite spindle poles (merotelic kinetochore orientation) (Cimini et al, 2001(Cimini et al, , 2002. Our results suggest that when HP1 is not correctly assembled on the centromeric heterochromatin in human cells, the less constrained centromeric organization may promote the attachment of individual kinetochores to microtubules coming from both spindle poles, thus producing anaphase-lagging chromosomes.…”

Detection and Correction of Merotelic Kinetochore Orientation by Aurora B and its Partners

“…24 Finally, merotelic attachments occur frequently in early mitosis 25 and are not detected by the spindle checkpoint. [26][27][28][29][30][31] Nevertheless, many of them are corrected before anaphase onset by an Aurora B-dependent mechanism, 25,32 as discussed later.…”

Microtubule-dependent Changes in Assembly of Microtubule Motor Proteins and Mitotic Spindle Checkpoint Proteins at PtK1 Kinetochores

“…This expanded crescent morphology may be a microtubule-dependent response of kinetochore assembly designed to substantially increase the solid angle for recruiting kinetochore microtubules under conditions where the density of spindle microtubules is very low. Conversely, kinetochores need to lose their expanded morphology upon kinetochore microtubule formation to prevent errors in chromosome segregation induced by attachment of individual kinetochores to microtubules from opposite poles (merotelic attachment; Cimini et al 2001) in addition to turning off the wait-anaphase signal of the mitotic spindle checkpoint (Rieder and Salmon, 1998;Howell et al, 2000).…”