The centromere geometry essential for keeping mitosis error free is controlled by spindle forces (original) (raw)
Related papers
Direct kinetochore-spindle pole connections are not required for chromosome segregation
The Journal of cell biology, 2014
Segregation of genetic material occurs when chromosomes move to opposite spindle poles during mitosis. This movement depends on K-fibers, specialized microtubule (MT) bundles attached to the chromosomes' kinetochores. A long-standing assumption is that continuous K-fibers connect every kinetochore to a spindle pole and the force for chromosome movement is produced at the kinetochore and coupled with MT depolymerization. However, we found that chromosomes still maintained their position at the spindle equator during metaphase and segregated properly during anaphase when one of their K-fibers was severed near the kinetochore with a laser microbeam. We also found that, in normal fully assembled spindles, K-fibers of some chromosomes did not extend to the spindle pole. These K-fibers connected to adjacent K-fibers and/or nonkinetochore MTs. Poleward movement of chromosomes with short K-fibers was uncoupled from MT depolymerization at the kinetochore. Instead, these chromosomes moved...
Molecular biology of the cell, 2015
Accuracy of chromosome segregation relies on the ill-understood ability of mitotic kinetochores to biorient, whereupon each sister kinetochore forms microtubule attachments to only one spindle pole. Since initial microtubule attachments result from chance encounters with the kinetochores, bi-orientation must rely on specific mechanisms to avoid and resolve improper attachments. Here, we use mathematical modeling to critically analyze the error-correction potential of a simplified bi-orientation mechanism, which involves the back-to-back arrangement of sister kinetochores and the marked instability of kinetochore-microtubule attachments. We show that a typical mammalian kinetochore operates in near optimal regime, in which the back-to-back kinetochore geometry and the indiscriminate kinetochore-microtubule turnover provide strong error-correction activity. In human cells, this mechanism alone can potentially enable normal segregation of 45 out of 46 chromosomes during one mitotic div...
Anaphase Spindle Mechanics Prevent Mis-Segregation of Merotelically Oriented Chromosomes
Current Biology, 2004
Hill series of the spindle and finding kinetochores with fluorescent fibers toward opposite poles. These cells were Chapel Hill, North Carolina 27599 imaged by time-lapse spinning-disk confocal microscopy . The collected images were analyzed, and both spindle poles and one or more kinetochore pairs Summary were tracked to determine kinetochore positioning and movement in metaphase and/or anaphase. We identified Merotelic kinetochore orientation is a kinetochore 54 merotelically oriented kinetochores (in 50 cells), and misattachment in which a single kinetochore is attached 25 of these were followed into anaphase. to microtubules from both spindle poles instead of Merotelically oriented kinetochores in metaphase exjust one. It can be favored in specific circumstances hibited several distinctive structural and kinetic features [1-5], is not detected by the mitotic checkpoint, and compared to those of normally oriented kinetochores. induces lagging chromosomes in anaphase . In In PtK1 cells, the outer face of a kinetochore is 0.3-0.5 mammalian cells, it occurs at high frequency in early m in diameter and contains about 24 kinetochore mi-
Chromosome congression in the absence of kinetochore fibres
Nature Cell Biology, 2009
Proper chromosome congression (the process of aligning chromosomes on the spindle) contributes to accurate and faithful chromosome segregation. It is widely accepted that congression requires 'K-fibres', microtubule bundles that extend from the kinetochores to spindle poles1 , 2. Here we demonstrate that chromosomes in human cells co-depleted for HSET (kinesin-14)3 , 4 and hNuf2 (a component of the Ndc80/Hec1 complex)5 can congress to the metaphase plate in the absence of K-fibres. However, the chromosomes were not stably maintained at the metaphase plate under these conditions. Chromosome congression in HSET+hNuf2 co-depleted cells required the plusend directed motor CENP-E (kinesin-7)6, which has been implicated in the gliding of monooriented kinetochores alongside adjacent K-fibres7. Thus, proper end-on attachment of kinetochores to microtubules is not necessary for chromosome congression. Instead, our data support the idea that congression allows unattached chromosomes to move to the middle of the spindle where they have a higher probability of establishing connections with both spindle poles. These bi-oriented connections are also utilized to maintain stable chromosome alignment at the spindle equator.
Self-organization of kinetochore-fibers in human mitotic spindles
2021
ABSTRACTDuring eukaryotic cell division, chromosomes are linked to microtubules (MTs) in the spindle by a macromolecular complex called the kinetochore. The bound kinetochore microtubules (KMTs) are crucial to ensuring accurate chromosome segregation. Recent electron tomography reconstructions (Kiewisz et al. 2021) captured the positions and configurations of every MT in human mitotic spindles, revealing that many KMTs in these spindles do not reach the pole. Here, we investigate the processes that give rise to this distribution of KMTs using a combination of analysis of the electron tomography reconstructions, photoconversion experiments, quantitative polarized light microscopy, and biophysical modeling. Our results indicate that in metaphase, KMTs grow away from the kinetochores along well-defined trajectories, continually decreasing in speed as they approach the poles. The locations of KMT minus ends, and the turnover and movements of tubulin in KMTs, are consistent with models i...
The Journal of Cell Biology, 1996
We used video-light microscopy and laser microsurgery to test the hypothesis that as a bioriented prometaphase chromosome changes position in PtK1 cells, the kinetochore moving away from its associated pole (AP) exerts a pushing force on the centromere. When we rapidly severed congressing chromosomes near the spindle equator between the sister kinetochores, the kinetochore that was originally "leading" the motion towards a pole (P) always (17/17 cells) continued moving P whereas the "trailing" kinetochore moving AP always stopped moving as soon as the operation was completed. This trailing kinetochore then initiated motion towards the pole it was originally moving away from up to 50 s later. The same result was observed (15/15 cells) when we selectively destroyed the leading (P moving) kinetochore on a congressing chromosome positioned 1>3 ~m from the pole it was moving away from. When we conducted this experiment on congressing chromosomes positioned within 3 txm of the pole, the centromere region either stopped moving, before switching into motion towards the near pole (2/4 cells), or it continued to move AP for 30-44 s (2/4 cells) before switching into P motion. Finally, kinetochorefree chromosome fragments, generated in the polar regions of PtK1 spindles, were ejected AP and often towards the spindle equator at ~2 ~rn/min. From these data we conclude that the kinetochore moving AP on a moving chromosome does not exert a significant pushing force on the chromosome. Instead, our results reveal that, when not generating a P force, kinetochores are in a "neutral" state that allows them to remain stationary or to coast AP in response to external forces sufficient to allow their K-fiber to elongate.
Chromosome Movement in Mitosis Requires Microtubule Anchorage at Spindle Poles
Journal of Cell Biology, 2001
Anchorage of microtubule minus ends at spindle poles has been proposed to bear the load of poleward forces exerted by kinetochore-associated motors so that chromosomes move toward the poles rather than the poles toward the chromosomes. To test this hypothesis, we monitored chromosome movement during mitosis after perturbation of nuclear mitotic apparatus protein (NuMA) and the human homologue of the KIN C motor family (HSET), two noncentrosomal proteins involved in spindle pole organization in animal cells. Perturbation of NuMA alone disrupts spindle pole organization and delays anaphase onset, but does not alter the velocity of oscillatory chromosome movement in prometaphase. Perturbation of HSET alone increases the duration of prometaphase, but does not alter the velocity of chromosome movement in prometaphase or anaphase. In contrast, simultaneous perturbation of both HSET and NuMA severely suppresses directed chromosome movement in prometaphase. Chromosomes coalesce near the cen...
Scientific Reports
Faithful chromosome segregation is ensured by the establishment of bi-orientation; the attachment of sister kinetochores to the end of microtubules extending from opposite spindle poles. In addition, kinetochores can also attach to lateral surfaces of microtubules; called lateral attachment, which plays a role in chromosome capture and transport. However, molecular basis and biological significance of lateral attachment are not fully understood. We have addressed these questions by focusing on the prometaphase rosette, a typical chromosome configuration in early prometaphase. We found that kinetochores form uniform lateral attachments in the prometaphase rosette. Many transient kinetochore components are maximally enriched, in an Aurora B activity-dependent manner, when the prometaphase rosette is formed. We revealed that rosette formation is driven by rapid poleward motion of dynein, but can occur even in its absence, through slow kinetochore movements caused by microtubule depolymerization that is supposedly dependent on kinetochore tethering at microtubule ends by CENP-E. We also found that chromosome connection to microtubules is extensively lost when lateral attachment is perturbed in cells defective in end-on attachment. Our findings demonstrate that lateral attachment is an important intermediate in bi-orientation establishment and chromosome alignment, playing a crucial role in incorporating chromosomes into the nascent spindle. For faithful chromosome segregation in mitosis, kinetochores on all the sister chromatid pairs have to establish bipolar attachment, or bi-orientation, which is the attachment of sister kinetochores to microtubules emanating from opposite spindle poles 1. On bi-oriented kinetochores, bundles of 20-30 microtubules, known as k-fibers, attach with their ends terminating at the kinetochore, in a manner called end-on attachment. This enables chromosome motion by the elongation and shrinkage of the k-fibers. In contrast, kinetochores can also attach to the sides of microtubules, referred to as lateral attachment, and move along microtubules mediated by the activities of motor proteins. The mechanism is conserved from yeast to humans 2. Kinetochores are efficiently captured by the lateral surface of microtubules and transported towards spindle poles 2 driven, in higher eukaryotes, by dynein 3,4. Recent studies revealed that lateral attachment in higher eukaryotes also plays a role in the accumulation of chromosomes to the spindle equator before they align on the so-called metaphase plate 5-7. We have recently reported that two motor proteins, Kid and CENP-E, play differential roles in this process 8. It has been suggested that bi-orientation is efficiently established for the chromosomes transported to the spindle equator through lateral