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Chromosome segregation errors during cell divisions generate aneuploidies and micronuclei, which can undergo extensive chromosomal rearrangements such as chromothripsis 1-5 . Selective pressures then shape distinct aneuploidy and rearrangement patterns-for example, in cancer 6,7 -but it is unknown whether initial biases in segregation errors and micronucleation exist for particular chromosomes. Using single-cell DNA sequencing 8 after an error-prone mitosis in untransformed, diploid cell lines and organoids, we show that chromosomes have different segregation error frequencies that result in non-random aneuploidy landscapes. Isolation and sequencing of single micronuclei from these cells showed that mis-segregating chromosomes frequently also preferentially become entrapped in micronuclei. A similar bias was found in naturally occurring micronuclei of two cancer cell lines. We find that segregation error frequencies of individual chromosomes correlate with their location in the interphase nucleus, and show that this is highest for peripheral chromosomes behind spindle poles. Randomization of chromosome positions, Cas9-mediated live tracking and forced repositioning of individual chromosomes showed that a greater distance from the nuclear centre directly increases the propensity to mis-segregate. Accordingly, chromothripsis in cancer genomes 9 and aneuploidies in early development 10 occur more frequently for larger chromosomes, which are preferentially located near the nuclear periphery. Our findings reveal a direct link between nuclear chromosome positions, segregation error frequencies and micronucleus content, with implications for our understanding of tumour genome evolution and the origins of specific aneuploidies during development., (© 2022. The Author(s).)

Human cancers harbor great numbers of genomic alterations. One of the most common alterations is aneuploidy, an imbalance at the chromosome level. Some aneuploid cancer cell populations show varying chromosome copy number alterations over time, a phenotype known as 'chromosomal instability' (CIN). Chromosome segregation errors in mitosis are the most common cause for CIN in vitro, and these are also thought to underlie the aneuploidies seen in clinical cancer samples. However, CIN and aneuploidy are different traits and they are likely to have distinct impacts on tumor evolution and clinical tumor behavior. In this opinion article, we discuss these differences and describe scenarios in which distinguishing them can be clinically relevant., (Copyright © 2016 Elsevier Inc. All rights reserved.)

Genetic mutations in the mitotic regulatory kinase BUBR1 are associated with the cancer-susceptible disorder mosaic variegated aneuploidy (MVA). In patients with biallelic mutations, a missense mutation pairs with a truncating mutation. Here, we show that cell lines derived from MVA patients with biallelic mutations have an impaired mitotic checkpoint, chromosome alignment defects, and low overall BUBR1 abundance. Ectopic expression of BUBR1 restored mitotic checkpoint activity, proving that BUBR1 dysfunction causes chromosome segregation errors in the patients. Combined analysis of patient cells and functional protein replacement shows that all MVA mutations fall in two distinct classes: those that impose specific defects in checkpoint activity or microtubule attachment and those that lower BUBR1 protein abundance. Low protein abundance is the direct result of the absence of transcripts from truncating mutants combined with high protein turnover of missense mutants. In this group of missense mutants, the amino acid change consistently occurs in or near the BUBR1 kinase domain. Our findings provide a molecular explanation for chromosomal instability in patients with biallelic genetic mutations in BUBR1.

Aneuploidy, an abnormal number of chromosomes, is a trait shared by most solid tumors. Chromosomal instability (CIN) manifested as aneuploidy might promote tumorigenesis and cause increased resistance to anti-cancer therapies. The mitotic checkpoint or spindle assembly checkpoint is a major signaling pathway involved in the prevention of CIN. We review current knowledge on the contribution of misregulation of mitotic checkpoint proteins to tumor formation and will address to what extent this contribution is due to chromosome segregation errors directly. We propose that both checkpoint and non-checkpoint functions of these proteins contribute to the wide array of oncogenic phenotypes seen upon their misregulation.

Abnormal chromosome content - also known as aneuploidy - is the most common characteristic of human solid tumours. It has therefore been proposed that aneuploidy contributes to, or even drives, tumour development. The mitotic checkpoint guards against chromosome mis-segregation by delaying cell-cycle progression through mitosis until all chromosomes have successfully made spindle-microtubule attachments. Defects in the mitotic checkpoint generate aneuploidy and might facilitate tumorigenesis, but more severe disabling of checkpoint signalling is a possible anticancer strategy.

Centromere-associated protein-E (CENP-E) is an essential mitotic kinesin that is required for efficient, stable microtubule capture at kinetochores. It also directly binds to BubR1, a kinetochore-associated kinase implicated in the mitotic checkpoint, the major cell cycle control pathway in which unattached kinetochores prevent anaphase onset. Here, we show that single unattached kinetochores depleted of CENP-E cannot block entry into anaphase, resulting in aneuploidy in 25% of divisions in primary mouse fibroblasts in vitro and in 95% of regenerating hepatocytes in vivo. Without CENP-E, diminished levels of BubR1 are recruited to kinetochores and BubR1 kinase activity remains at basal levels. CENP-E binds to and directly stimulates the kinase activity of purified BubR1 in vitro. Thus, CENP-E is required for enhancing recruitment of its binding partner BubR1 to each unattached kinetochore and for stimulating BubR1 kinase activity, implicating it as an essential amplifier of a basal mitotic checkpoint signal.

Aneuploidy is a hallmark of cancer and a major cause of miscarriages in humans. It is caused by chromosome segregation errors during cell divisions. Evidence is mounting that the probability of specific chromosomes undergoing a segregation error is non-random. In other words, some chromosomes have a higher chance of contributing to aneuploid karyotypes than others. This could have important implications for the origins of recurrent aneuploidy patterns in cancer and developing embryos. Here, we review recent progress in understanding the prevalence and causes of non-random chromosome segregation errors in mammalian mitosis and meiosis. We evaluate its potential impact on cancer and human reproduction and discuss possible research avenues. [ABSTRACT FROM AUTHOR]

Aneuploidy is the leading cause of miscarriage and congenital birth defects, and a hallmark of cancer. Despite this strong association with human disease, the genetic causes of aneuploidy remain largely unknown. Through exome sequencing of patients with constitutional mosaic aneuploidy, we identified biallelic truncating mutations in CENATAC (CCDC84). We show that CENATAC is a novel component of the minor (U12‐dependent) spliceosome that promotes splicing of a specific, rare minor intron subtype. This subtype is characterized by AT‐AN splice sites and relatively high basal levels of intron retention. CENATAC depletion or expression of disease mutants resulted in excessive retention of AT‐AN minor introns in ˜ 100 genes enriched for nucleocytoplasmic transport and cell cycle regulators, and caused chromosome segregation errors. Our findings reveal selectivity in minor intron splicing and suggest a link between minor spliceosome defects and constitutional aneuploidy in humans. SYNOPSIS: Genetic causes of aneuploidy in humans remain largely unknown. Here, patient exome sequencing reveals pathogenic patient mutations in CENATAC/CCDC84, encoding a novel component of the minor spliceosome, and downstream effects on chromosome segregation in mitosis. Pathogenic mutations in CENATAC were identified in two siblings with Mosaic Variegated Aneuploidy syndrome.CENATAC is a novel component of the minor (U12‐dependent) spliceosome di‐ and tri‐snRNP complexes.CENATAC malfunction leads to defective splicing of minor introns characterized by reduced intrinsic splicing activity, predominantly those with AT‐AN splice sites.CENATAC malfunction leads to defective chromosome congression in mitosis.CENATAC's mitotic phenotype is a secondary effect of defective minor spliceosome function. [ABSTRACT FROM AUTHOR]

Most human cancers are aneuploid, due to a chromosomal instability (CIN) phenotype. Despite being hallmarks of cancer, however, the roles of CIN and aneuploidy in tumor formation have not unequivocally emerged from animal studies and are thus still unclear. Using a conditional mouse model for diverse degrees of CIN, we find that a particular range is sufficient to drive very early onset spontaneous adenoma formation in the intestine. In mice predisposed to intestinal cancer (ApcMin/+), moderate CIN causes a remarkable increase in adenoma burden in the entire intestinal tract and especially in the distal colon, which resembles human disease. Strikingly, a higher level of CIN promotes adenoma formation in the distal colon even more than moderate CIN does, but has no effect in the small intestine. Our results thus show that CIN can be potently oncogenic, but that certain levels of CIN can have contrasting effects in distinct tissues. Aneuploidy caused by chromosomal instability is frequently observed in cancer, but little is known about its contribution to tumor development. Here, the authors show that in the mouse intestine, the consequences of aneuploidy are exquisitely dependent on both its extent and anatomical location. [ABSTRACT FROM AUTHOR]

Crypt stem cells represent the cells of origin for intestinal neoplasia. Both mouse and human intestinal stem cells can be cultured in medium containing the stem-cell-niche factors WNT, R-spondin, epidermal growth factor (EGF) and noggin over long time periods as epithelial organoids that remain genetically and phenotypically stable. Here we utilize CRISPR/Cas9 technology for targeted gene modification of four of the most commonly mutated colorectal cancer genes (APC, P53 (also known as TP53), KRAS and SMAD4) in cultured human intestinal stem cells. Mutant organoids can be selected by removing individual growth factors from the culture medium. Quadruple mutants grow independently of all stem-cell-niche factors and tolerate the presence of the P53 stabilizer nutlin-3. Upon xenotransplantation into mice, quadruple mutants grow as tumours with features of invasive carcinoma. Finally, combined loss of APC and P53 is sufficient for the appearance of extensive aneuploidy, a hallmark of tumour progression. [ABSTRACT FROM AUTHOR]

Background: Chromosomal instability (CIN), a feature widely shared by cells from solid tumors, is caused by occasional chromosome missegregations during cell division. Two of the causes of CIN are weakened mitotic checkpoint signaling and persistent merotelic attachments that result in lagging chromosomes during anaphase. Principal Findings: Here we identify an autophosphorylation event on Mps1 that is required to prevent these two causes of CIN. Mps1 is phosphorylated in mitotic cells on at least 7 residues, 4 of which by autophosphorylation. One of these, T676, resides in the activation loop of the kinase domain and a mutant that cannot be phosphorylated on T676 is less active than wild-type Mps1 but is not kinase-dead. Strikingly, cells in which endogenous Mps1 was replaced with this mutant are viable but missegregate chromosomes frequently. Anaphase is initiated in the presence of misaligned and lagging chromosomes, indicative of a weakened checkpoint and persistent merotelic attachments, respectively. Conclusions/Significance: We propose that full activity of Mps1 is essential for maintaining chromosomal stability by allowing resolution of merotelic attachments and to ensure that single kinetochores achieve the strength of checkpoint signaling sufficient to prevent premature anaphase onset and chromosomal instability. To our knowledge, phosphorylation of T676 on Mps1 is the first post-translational modification in human cells of which the absence causes checkpoint weakening and CIN without affecting cell viability. [ABSTRACT FROM AUTHOR]

Various types of chromosomal aberrations, including numerical (aneuploidy) and structural (e.g., translocations, deletions), are commonly found in human tumors and are linked to tumorigenesis. Aneuploidy is a direct consequence of chromosome segregation errors in mitosis, whereas structural aberrations are caused by improperly repaired DNA breaks. Here, we demonstrate that chromosome segregation errors can also result in structural chromosome aberrations. Chromosomes that missegregate are frequently damaged during cytokinesis, triggering a DNA double-strand break response in the respective daughter cells involving ATM, Chk2, and p53. We show that these double-strand breaks can lead to unbalanced translocations in the daughter cells. Our data show that segregation errors can cause translocations and provide insights into the role of whole-chromosome instability in tumorigenesis. [ABSTRACT FROM AUTHOR]