Chromosome missegregation in human cells arises through specific types of kinetochore–microtubule attachment errors

Abstract

Most solid tumors are aneuploid, and many missegregate chromosomes at high rates in a phenomenon called chromosomal instability (CIN). CIN reflects the erosion of mitotic fidelity, and it correlates with poor patient prognosis and drug resistance. The most common mechanism causing CIN is the persistence of improper kinetochore-microtubule attachments called merotely. Chromosomes with merotelic kinetochores often manifest as lagging chromosomes in anaphase, suggesting that lagging chromosomes fail to segregate properly. However, it remains unknown whether the lagging chromosomes observed in anaphase segregate to the correct or incorrect daughter cell. To address this question, we tracked the segregation of a single human chromosome during cell division by using LacI-GFP to target an integrated LacO array. By scoring the distribution of each sister chromatid during mitosis, we show that a majority of lagging chromosomes in anaphase segregate to the correct daughter cell. Instead, sister chromatids that segregate erroneously frequently do so without obvious evidence of lagging during anaphase. This outcome is expected if sister kinetochores on a chromosome bind microtubules oriented toward the same spindle pole, and we find evidence for syntelic kinetochore attachments in cells after treatments that increase missegregation rates. Thus, lagging chromosomes in anaphase are symptomatic of defects in kinetochore-microtubule attachment dynamics that cause chromosome missegregation associated with CIN, but the laggards rarely missegregate.aneuploidy | syntely | MCAK | micronuclei | genome instability S olid tumors are frequently aneuploid and many missegregate chromosomes at high rates in a phenomenon called chromosomal instability (CIN; refs. 1 and 2). CIN is associated with poor patient prognosis, and various studies have shown that it correlates with advanced tumor stage including acquisition of metastatic potential and drug resistance (3-5). It has been proposed that by frequently changing the karyotype of tumor cells, that CIN provides an agent of change that drives the evolution of tumor cell phenotypes (3-8). The treatment difficulties encountered in advanced stage tumors underscores the importance of determining the mechanisms of CIN and how they contribute to tumor growth.Various mechanisms have been proposed to cause CIN including dysfunction of the spindle assembly checkpoint, defects in sister chromatid cohesion, and defects in the attachment of chromosomes to spindle microtubules (2). Recently, live cell imaging demonstrated that the most common cause of CIN is the persistence of errors in the attachment of spindle microtubules to chromosomes (9, 10). Microtubules bind to chromosomes at specialized structures called kinetochores. Each chromosome has a pair of kinetochores, and faithful chromosome segregation arises when single kinetochores bind microtubules oriented toward only one spindle pole resulting in the biorientation of chromosomes on the spindle. However, errors in the orientation of kinetochore-mic...

Lagging chromosomes entrapped in micronuclei are not 'lost' by cells

“…Infrequently (6.67%-15.38%), the laggards ultimately moved to the incorrect side and produced a trisomic daughter cell with the laggard in micronucleus and a monosomic cell. Consistently, it has been indicated that micronucleus was more likely to reside in the correct cells [9]. Thus, most lagging chromosomes do not directly produce aneuploid progenies, but are entrapped in the micronuclei of correct daughter cells.…”

“…Possible scenarios for the fates of the micronuclei include: (1) expulsion from the cell [3]; (2) apoptosis independent of the cell [2]; (3) removal by autophagy [4]; (4) retention within the cytoplasm as an extra-nuclear entity despite cell division [6]; or (5) reincorporation into the main nucleus [9]. The first four scenarios would cause genetic material loss from the cell.…”

Integrity of the human centromere DNA repeats is protected by CENP-A, CENP-C, and CENP-T

“…The centromere instability was not limited to CIN cancer cell lines (U2OS, HeLa, and MCF7) but also found in karyotypically stable HCT116 cells (41), which is yet defective in intra-S-checkpoint activation during replication and in DNA damage repair (48). Except for U2OS, cancer cell lines used in this study showed a decrease in chromatin-bound CENP-A.…”

“…Monastrol is an inhibitor of Eg5 that causes mitotic arrest with monopolar spindles (38). When monastrol is washed out, many kinetochores form merotelic and syntelic attachments, causing chromosome missegregation (39)(40)(41). Monastrol caused micronuclei formation (SI Appendix, patterns in these cells (SI Appendix, Fig.…”

p14ARF Prevents Proliferation of Aneuploid Cells by Inducing p53‐Dependent Apoptosis

“…The MCC binds and inhibits the Anaphase-Promoting Complex/Cyclosome (APC/C) avoiding chromosome mis-segregation (Silva et al, 2011). Defective mitoses, caused by weakening the SAC, could promote aneuploidy characterized by numerical and structural changes of chromosomes that contribute to genomic instability, typical of many human tumors (Weaver and Cleveland, 2009;Thompson and Compton, 2011). However, it is not yet clearly established if aneuploidy is a cause of tumor initiation.…”