Spindle Assembly Checkpoint Genes Research Articles

Deletion of the MAD2L1 spindle assembly checkpoint gene is tolerated in mouse models of acute T-cell lymphoma and hepatocellular carcinoma.

Chromosome instability (CIN) is deleterious to normal cells because of the burden of aneuploidy. However, most human solid tumors have an abnormal karyotype implying that gain and loss of chromosomes by cancer cells confers a selective advantage. CIN can be induced in the mouse by inactivating the spindle assembly checkpoint. This is lethal in the germline but we show here that adult T cells and hepatocytes can survive conditional inactivation of the Mad2l1 SAC gene and resulting CIN. This causes rapid onset of acute lymphoblastic leukemia (T-ALL) and progressive development of hepatocellular carcinoma (HCC), both lethal diseases. The resulting DNA copy number variation and patterns of chromosome loss and gain are tumor-type specific, suggesting differential selective pressures on the two tumor cell types.

Extract of bulbus Fritillaria cirrhosa perturbs spindle assembly checkpoint, induces mitotic aberrations and genomic instability in human colon epithelial cell line

BackgroundBulbus Fritillaria cirrhosa D. Don (BFC) has been used in China as a folk medicine for the treatment of cough and asthma for more than 2000 years. The antitussive and antiasthmatic effects of BFC have been reported before, nevertheless its toxicity and safety have not been documented. This study investigated the possible effects of BFC on spindle assembly checkpoint (SAC), mitotic fidelity and genomic stability in human NCM460 colon epithelial cells. MethodsCells were treated with BFC (0, 20, 40, 80 and 160μg/ml) for 24, 48 and 72h and harvested differently according to the biomarkers observed. Mitotic aberrations were assessed by the biomarkers of chromosome misalignment (CMA), chromosome lagging (CL) and chromatin bridge (CB). Frequencies of micronuclei (MN), nucleoplasmic bridge and nuclear bud (NB) in cytokinesis-block micronucleus assay were used as indicators of genomic instability (GIN). SAC activity was determined by anaphase to metaphase ratio (AMR) and the expression of several SAC genes, including CENP-E, Mps1, Bub1, Mad-1, BubR1 and Mad-2. ResultsCompared with the control, cells in BFC treated groups (80 and 160μg/ml) showed: 1) increased AMR (p<0.05), up-regulated expression of Mps1, Bub1 and Mad-1 (p<0.05) and down-regulated expression of CENP-E, BubR1 and Mad-2 (p<0.05); 2) increased frequencies of CMA, CL and CB (p<0.01); 3) increased incidences of MN and NB (p<0.01). ConclusionsThis study revealed for the first time that BFC causes mitotic aberrations and GIN in human colon epithelial cells and these effects maybe the result of SAC dysfunction.

Phyllanthus emblica Fruit Extract Activates Spindle Assembly Checkpoint, Prevents Mitotic Aberrations and Genomic Instability in Human Colon Epithelial NCM460 Cells.

The fruit of Phyllanthus emblica Linn. (PE) has been widely consumed as a functional food and folk medicine in Southeast Asia due to its remarkable nutritional and pharmacological effects. Previous research showed PE delays mitotic progress and increases genomic instability (GIN) in human colorectal cancer cells. This study aimed to investigate the similar effects of PE by the biomarkers related to spindle assembly checkpoint (SAC), mitotic aberrations and GIN in human NCM460 normal colon epithelial cells. Cells were treated with PE and harvested differently according to the biomarkers observed. Frequencies of micronuclei (MN), nucleoplasmic bridge (NPB) and nuclear bud (NB) in cytokinesis-block micronucleus assay were used as indicators of GIN. Mitotic aberrations were assessed by the biomarkers of chromosome misalignment, multipolar division, chromosome lagging and chromatin bridge. SAC activity was determined by anaphase-to- metaphase ratio (AMR) and the expression of core SAC gene budding uninhibited by benzimidazoles related 1 (BubR1). Compared with the control, PE-treated cells showed (1) decreased incidences of MN, NPB and NB (p < 0.01); (2) decreased frequencies of all mitotic aberration biomarkers (p < 0.01); and (3) decreased AMR (p < 0.01) and increased BubR1 expression (p < 0.001). The results revealed PE has the potential to protect human normal colon epithelial cells from mitotic and genomic damages partially by enhancing the function of SAC.

Abstract 3588: The spindle assembly checkpoint gene Bub1b is essential for the survival of some breast cancers

Abstract As normal breast epithelium evolves towards malignancy, cells accumulate genomic changes that give them a replicative advantage while at the same time increasing their genomic instability. Increased genomic instability results in accumulation of genomic aberrations that compromise the genomic integrity and, therefore, threaten cell viability, thus putting cancer cells under mitotic stress. As a consequence, cancer cells evolutionarily must adapt themselves to compete with the possible detrimental effects of genomic instability. Finding a balance between the instability that gives them a replicative advantage and the instability that could lead them to mitotic catastrophe is crucial. The mitotic stress caused by genomic instability may require overexpression of certain spindle assembly checkpoint (SAC) genes, which can prevent mitotic catastrophe that would occur if cancer cells undergo mitosis prematurely. Although the full mechanism of action of SAC is yet to be elucidated, Bub1b through its protein BubR1 is an important part of this checkpoint, and inhibits the onset of anaphase until all chromosomes are aligned correctly at the metaphase plate. Our analysis of clinical datasets shows a significant increase in the expression of Bub1b in breast cancer as compared to normal epithelia. Furthermore, Bub1b overexpression correlates with decreased overall survival in patient samples. Our analyses also show a pattern of increasing Bub1b overexpression in more aggressive variants of breast cancer such as triple negative tumors and high-grade tumors, which also tend to be more resistant to current therapies. Expression analyses of breast cancer cell lines reveal that Bub1b overexpression is positively correlated with more aggressive behavior. We postulated that the requirement for Bub1b expression might be a vulnerability of rapidly proliferating cancers; therefore, its inhibition will result in cell death through mitotic catastrophe. Using RNA interference with siRNAs, we reduced Bub1b levels in a variety of breast cancer cells. Our results showed significant decrease in cell viability and clonogenicity in soft agar upon Bub1b knockdown, especially in triple negative breast cancer cell lines. However, the viability of normal breast epithelium cells, MCF12A, was not affected. Our data indicate that Bub1b is a critical player in breast cancer viability, and further investigation of the role of Bub1b in promoting successful proliferation of breast cancer cells with genomic instability could provide a new therapeutic strategy particularly in concert with standard genotoxic treatments such as alkylators, spindle poisons and radiation therapy. Citation Format: Dilara Koyuncu, Erik T. Goka, Philip C. Miller, Marc E. Lippman. The spindle assembly checkpoint gene Bub1b is essential for the survival of some breast cancers. [abstract]. In: Proceedings of the 107th Annual Meeting of the American Association for Cancer Research; 2016 Apr 16-20; New Orleans, LA. Philadelphia (PA): AACR; Cancer Res 2016;76(14 Suppl):Abstract nr 3588.

Prevalence of germline mutations in the spindle assembly checkpoint gene BUB1B in individuals with early-onset colorectal cancer.

Germline mutations in BUB1B, encoding BUBR1, one of the crucial components of the spindle assembly checkpoint (SAC), have been shown to cause variable phenotypes, including the recessive mosaic variegated aneuploidy (MVA) syndrome, which predisposes to cancer. Reduced levels of the wild-type BUBR1 protein have been linked to the development of gastrointestinal neoplasms. To determine whether mutations in BUB1B are enriched in individuals with colorectal cancer (CRC), we performed amplicon-based targeted next-generation sequencing of BUB1B on germline DNA of 192 individuals with early-onset CRC (≤50 years). None of the individuals was found to be homozygous or compound heterozygous for mutations in BUB1B. However, we did identify two rare heterozygous variants, p.Glu390del and p.Cys945Tyr, in patients who developed CRC at the ages of 41 and 43 years, respectively. Both variants were shown not to affect BUBR1 protein expression levels and protein localization. Since the p.Glu390del variant is located in the BUB3-binding domain, we also performed immunoprecipitation to examine whether this variant affects the binding of BUB1 or BUB3 to BUBR1 but, compared to wild-type BUBR1, no difference was observed. Our data suggest that mutations in BUB1B do not occur frequently in the germline of individuals with CRC and that BUB1B unlikely plays a major role in the predisposition to early-onset CRC. Whether carriers of pathogenic BUB1B mutations, such as the parents of MVA syndrome patients, have an increased risk for cancer remains of interest, as studies in mice have suggested that haploinsufficiency of BUB1B may cause an increase in carcinogen-induced tumors. © 2016 Wiley Periodicals, Inc.

Deregulation of HMGA1 expression induces chromosome instability through regulation of spindle assembly checkpoint genes.

The mitotic spindle assembly checkpoint (SAC) is an essential control system of the cell cycle that contributes to mantain the genomic stability of eukaryotic cells. SAC genes expression is often deregulated in cancer cells, leading to checkpoint impairment and chromosome instability. The mechanisms responsible for the transcriptional regulation and deregulation of these genes are still largely unknown. Herein we identify the nonhistone architectural nuclear proteins High Mobility Group A1 (HMGA1), whose overexpression is a feature of several human malignancies and has a key role in cancer progression, as transcriptional regulators of SAC genes expression. In particular, we show that HMGA1 proteins are able to increase the expression of the SAC genes Ttk, Mad2l1, Bub1 and Bub1b, binding to their promoter regions. Consistently, HMGA1-depletion induces SAC genes downregulation associated to several mitotic defects. In particular, we observed a high number of unaligned chromosomes in metaphase, a reduction of prometaphase time, a delay of anaphase, a higher cytokinesis time and a higher percentage of cytokinesis failure by using live-cell microscopy. Finally, a significant direct correlation between HMGA1 and SAC genes expression was detected in human colon carcinomas indicating a novel mechanism by which HMGA1 contributes to cancer progression.

Association between single nucleotide polymorphisms (SNPs) of genes involved in spindle assembly checkpoint (SAC) and clinical outcomes in advanced gastric cancer (AGC) patients (pts) treated with taxane-based chemotherapy.

79 Background: Taxanes which disrupt the microtubule function and inhibit the process of cell division have shown encouraging activity in the treatment of AGC. Resistance to these agents often becomes a problem in clinical settings and its mechanism hasn’t been dissolved conclusively. SAC is a safety device ensures the proper chromosome segregation in mitosis and is required for taxane-induced cell death. We hypothesized genetic variants in SAC genes may be associated with clinical outcomes in pts with AGC treated with taxane. Methods: Genomic DNA was isolated from blood or tissue samples of 39 U.S. pts (median age 57; median follow-up 6.4 months) for evaluation set and 39 Japanese (JPN) pts (median age 63; median follow-up 9.4 months) for validation set, with AGC treated with taxane. Twenty-five functionally significant SNPs in SAC genes (MAD1, MAD2, BUB3, BUBR1, RAN, TPX2, CDC20, AURKA, AURKB, RCC1, ANAPC10, ANAPC13) were analyzed by PCR-based direct sequencing and evaluated for association with outcomes. Results: In univariate analysis, rs4236271 (MAD1), rs6954673 (MAD1), and rs2064863 (AURKA) showed a significant difference in 6-month (mo) progression-free survival (PFS) rate [(C/C 42%, C/T 12%; HR 2.66, P=0.008), (C/C 75%, C/T or T/T 24%; HR 5.10, P=0.008), and (T/T 50%, T/G 15%, G/G 57%; HR1.55, P=0.046), respectively] and 18-mo overall survival (OS) rate [(C/C 40%, C/T 8%; HR3.69, P&lt;0.001), (C/C 56%, C/T or T/T 19%; HR3.60, P=0.004), and (T/T 59%, T/G 15%, G/G 29%; HR 2.02, P=0.047), respectively] in evaluation set. In multivariate analysis, rs4236271 and rs6954673 remained significant in PFS (HR 7.24, P=0.005, HR 14.49, P=0.015, respectively) and OS (HR 7.39, P=0.001, HR 6.37, P=0.002, respectively). In validation set, rs6954763 showed a significant difference in 18-mo OS rate (C/C 16%, C/T or T/T 47%, HR 3.55, P=0.014), but the impact of C/C genotype on OS in the JPN pts was the opposite to the U.S. pts. Conclusions: These results suggest that MAD1 polymorphisms may serve as a prognostic marker in pts with AGC. Further studies using larger population are needed to corroborate our results.

Chromosome instability induced by Mps1 and p53 mutation generates aggressive lymphomas exhibiting aneuploidy-induced stress.

Aneuploidy is a hallmark of human solid cancers that arises from errors in mitosis and results in gain and loss of oncogenes and tumor suppressors. Aneuploidy poses a growth disadvantage for cells grown in vitro, suggesting that cancer cells adapt to this burden. To understand better the consequences of aneuploidy in a rapidly proliferating adult tissue, we engineered a mouse in which chromosome instability was selectively induced in T cells. A flanked by Lox mutation was introduced into the monopolar spindle 1 (Mps1) spindle-assembly checkpoint gene so that Cre-mediated recombination would create a truncated protein (Mps1(DK)) that retained the kinase domain but lacked the kinetochore-binding domain and thereby weakened the checkpoint. In a sensitized p53(+/-) background we observed that Mps1(DK/DK) mice suffered from rapid-onset acute lymphoblastic lymphoma. The tumors were highly aneuploid and exhibited a metabolic burden similar to that previously characterized in aneuploid yeast and cultured cells. The tumors nonetheless grew rapidly and were lethal within 3-4 mo after birth.

Tumor suppressor roles of CENP-E and Nsl1 in Drosophila epithelial tissues

Depletion of spindle assembly checkpoint (SAC) genes in Drosophila epithelial tissues leads to JNK-dependent programmed cell death and additional blockade of the apoptotic program drives tumorigenesis. A recent report proposes that chromosomal instability (CIN) is not the driving force in the tumorigenic response of the SAC-deficient tissue, and that checkpoint proteins exert a SAC-independent tumor suppressor role. This notion is based on observations that the depletion of CENP-E levels or prevention of Bub3 from binding to the kinetochore in Drosophila tissues unable to activate the apoptotic program induces CIN but does not cause hyperproliferation. Here we re-examined this proposal. In contrast to the previous report, we observed that depletion of CENP-E or Nsl1—the latter mediating kinetochore targeting of Bub3—in epithelial tissues unable to activate the apoptotic program induces significant levels of aneuploidy and drives tumor-like growth. The induction of the JNK transcriptional targets Wingless, a mitogenic molecule, and MMP1, a matrix metaloproteinase 1 involved in basement membrane degradation was also observed in these tumors. An identical response of the tissue was previously detected upon depletion of several SAC genes or genes involved in spindle assembly, chromatin condensation, and cytokinesis, all of which have been described to cause CIN. All together, these results reinforce the role of CIN in driving tumorigenesis in Drosophila epithelial tissues and question the proposed SAC-independent roles of checkpoint proteins in suppressing tumorigenesis. Differences in aneuploidy rates might explain the discrepancy between the previous report and our results.

Spindle assembly checkpoint gene expression in childhood adrenocortical tumors (ACT): Overexpression of Aurora kinases A and B is associated with a poor prognosis

Pediatric adrenocortical tumors (ACT) are rare malignancies and treatment has a small impact on survival in advanced disease and the discovery of potential target genes could be important in new therapeutic approaches. The mRNA expression levels of spindle checkpoint genes AURKA, AURKB, BUB, and BUBR1 were analyzed in 60 children with ACT by quantitative real time PCR. The anticancer effect of ZM447439, an experimental AURK inhibitor, was analyzed in a primary childhood ACT culture carrying the TP53 p.R337H mutation. A significant association was observed between malignancy as defined by Weiss score ≥3 and higher AURKA (2.0-fold, P = 0.01), AURKB (7.0-fold, P = 0.007), and BUBR1 (5.8-fold, P = 0.007) gene expression, and between unfavorable event (death or relapse) and higher expression of AURKA (6.0-fold, P = 0.034) and AURKB (17-fold, P = 0.013). Overexpression of AURKA and AURKB was associated with lower event-free survival in uni- (P < 0.001 and P = 0.006, respectively) and multivariate (P = 0.002 and P = 0.03, respectively) analysis. Significant lower Event free survival (EFS) was also observed in patients with moderate/strong immunostaining to AURKA (P = 0.012) and AURKB (P = 0.045). ZM447439 was able to induce inhibition of proliferation and colony formation in a primary childhood ACT culture carrying the TP53 p.R337H mutation. Our results suggest that AURKA and AURKB overexpression in pediatric ACT may be related to more aggressive disease and the inhibition of these proteins could be an interesting approach for the treatment of these tumors.

Germline Mutations in the Spindle Assembly Checkpoint Genes BUB1 and BUB3 Are Risk Factors for Colorectal Cancer

The spindle assembly checkpoint controls proper chromosome segregation during mitosis and prevents aneuploidy-an important feature of cancer cells. We performed genome-wide and targeted copy number and mutation analyses of germline DNA from 208 patients with familial or early-onset (40 years of age or younger) colorectal cancer; we identified haploinsufficiency or heterozygous mutations in the spindle assembly checkpoint genes BUB1 and BUB3 in 2.9% of them. Besides colorectal cancer, these patients had variegated aneuploidies in multiple tissues and variable dysmorphic features. These results indicate that mutations in BUB1 and BUB3 cause mosaic variegated aneuploidy and increase the risk of colorectal cancer at a young age.

A tumor suppressor role of the Bub3 spindle checkpoint protein after apoptosis inhibition

Most solid tumors contain aneuploid cells, indicating that the mitotic checkpoint is permissive to the proliferation of chromosomally aberrant cells. However, mutated or altered expression of mitotic checkpoint genes accounts for a minor proportion of human tumors. We describe a Drosophila melanogaster tumorigenesis model derived from knocking down spindle assembly checkpoint (SAC) genes and preventing apoptosis in wing imaginal discs. Bub3-deficient tumors that were also deficient in apoptosis displayed neoplastic growth, chromosomal aneuploidy, and high proliferative potential after transplantation into adult flies. Inducing aneuploidy by knocking down CENP-E and preventing apoptosis does not induce tumorigenesis, indicating that aneuploidy is not sufficient for hyperplasia. In this system, the aneuploidy caused by a deficient SAC is not driving tumorigenesis because preventing Bub3 from binding to the kinetochore does not cause hyperproliferation. Our data suggest that Bub3 has a nonkinetochore-dependent function that is consistent with its role as a tumor suppressor.

Abstract 3814: Exome sequencing for identification of causative genes for mosaic variegated aneuploidy.

Abstract Mosaic Variegated Aneuploidy (MVA: OMIM 257300) is a rare autosomal recessive syndrome associated with growth deficiency of prenatal onset, microcephaly, intellectual disability, anomalies of the central nervous system, mild physical dysmorphic features and predisposition to cancer. Of the 37 reported cases of MVA, the cancers reported include Wilms tumor, rhabdomyosarcoma and leukemia. The cells from MVA patients demonstrate variable whole chromosome loss and gains suggesting an underlying chromosome segregation dysfunction. Previous studies have demonstrated biallelic loss-of-function mutations in mitotic spindle-assembly checkpoint gene BUB1B or a centrosomal microtubule stabilizing gene CEP57 in some MVA patients. Therefore, the goal of this project is to identify novel causative genes that contribute to the development of MVA. We have identified one patient diagnosed with clinical features of MVA associated with myelodysplasia and acute myeloid leukemia. Cytogenetic analysis of peripheral blood karyotype demonstrated low-level mosaicism with multiple clones of various chromosomal gains such as trisomy 1, 5, 6, 8 and 18. Molecular sequence analysis confirmed normal BUB1B and CEP57 in this patient. Therefore, whole-exome sequencing is being used as an approach to identify disease-causing genes in our patient. Exome data analysis assuming an autosomal recessive model and Sanger sequencing confirmed four putative genes with biallelic mutations in AIM1 (absent in melanoma 1), EPS15 (epidermal growth factor receptor substrate 15), MICALL2 (molecule interacting with CasL-like protein 2) and ZSCAN12 (zinc finger and SCAN domain containing 12). Review of literature reveals potential roles of these genes on cytoskeleton, mitotic spindle formation and cytokinesis. To further investigate these potential loci in our MVA patient, we designed cellular and functional assays using patient skin fibroblasts. Using interphase-FISH analysis, we have recapitulated the aneuploidy phenotype with abnormal chromosome numbers involving trisomy 8 in the patient skin fibroblasts. Moreover, immunocytochemistry with cytoskeletal and mitotic markers display aberrant anaphase with dysfunctional spindle mid-zone and cytokinesis failure. In addition, the patient fibroblasts also exhibited increased percentage of binucleated and micronucleated progeny due to abnormal chromosome segregation and cytokinesis. In summary, exome sequencing revealed a small number of potential causative genes as the etiology of MVA in our patient. Our early results demonstrate biomarkers for chromosome instability and aneuploidy such as non-disjunction, cytokinesis failure, micronuclei and binucleation in patient fibroblasts. Further work will determine whether dysregulation of these candidate genes can recapitulate this instability phenotype leading to mosaic aneuploidy in our patient. Citation Format: Sirisha Peddibhotla, Bradford Powell, Meha P. Patel, Pulivarthi H. Rao, David A. Wheeler, Richard A. Gibbs, Sharon E. Plon. Exome sequencing for identification of causative genes for mosaic variegated aneuploidy. [abstract]. In: Proceedings of the 104th Annual Meeting of the American Association for Cancer Research; 2013 Apr 6-10; Washington, DC. Philadelphia (PA): AACR; Cancer Res 2013;73(8 Suppl):Abstract nr 3814. doi:10.1158/1538-7445.AM2013-3814

Spindle checkpoint deficiency is tolerated by murine epidermal cells but not hair follicle stem cells.

The spindle assembly checkpoint (SAC) ensures correct chromosome segregation during mitosis by preventing aneuploidy, an event that is detrimental to the fitness and survival of normal cells but oncogenic in tumor cells. Deletion of SAC genes is incompatible with early mouse development, and RNAi-mediated depletion of SAC components in cultured cells results in rapid death. Here we describe the use of a conditional KO of mouse Mad2, an essential component of the SAC signaling cascade, as a means to selectively induce chromosome instability and aneuploidy in the epidermis of the skin. We observe that SAC inactivation is tolerated by interfollicular epidermal cells but results in depletion of hair follicle bulge stem cells. Eventually, a histologically normal epidermis develops within ∼1 mo after birth, albeit without any hair. Mad2-deficient cells in this epidermis exhibited abnormal transcription of metabolic genes, consistent with aneuploid cell state. Hair follicle bulge stem cells were completely absent, despite the continued presence of rudimentary hair follicles. These data demonstrate that different cell lineages within a single tissue respond differently to chromosome instability: some proliferating cell lineages can survive, but stem cells are highly sensitive.

MiR-125b promotes cell death by targeting spindle assembly checkpoint gene MAD1 and modulating mitotic progression

The spindle assembly checkpoint (SAC) is a 'wait-anaphase' mechanism that has evolved in eukaryotic cells in response to the stochastic nature of chromosome-spindle attachments. In the recent past, different aspects of the SAC regulation have been described. However, the role of microRNAs in the SAC is vaguely understood. We report here that Mad1, a core SAC protein, is repressed by human miR-125b. Mad1 serves as an adaptor protein for Mad2 - which functions to inhibit anaphase entry till the chromosomal defects in metaphase are corrected. We show that exogenous expression of miR-125b, through downregulation of Mad1, delays cells at metaphase. As a result of this delay, cells proceed towards apoptotic death, which follows from elevated chromosomal abnormalities upon ectopic expression of miR-125b. Moreover, expressions of Mad1 and miR-125b are inversely correlated in a variety of cancer cell lines, as well as in primary head and neck tumour tissues. We conclude that increased expression of miR-125b inhibits cell proliferation by suppressing Mad1 and activating the SAC transiently. We hypothesize an optimum Mad1 level and thus, a properly scheduled SAC is maintained partly by miR-125b.

523 Levels of Anaphase Bridge Formation and Spindle Assembly Checkpoint Genes Are Significantly Affected by Obesity and Radiosensitivity Status in Oesophageal Cancer Patients

523 Levels of Anaphase Bridge Formation and Spindle Assembly Checkpoint Genes Are Significantly Affected by Obesity and Radiosensitivity Status in Oesophageal Cancer Patients

OC-123 Obesity drives radioresistance and enhances genomic instability in oesophageal adenocarcinoma

IntroductionObesity is strongly associated with oesophageal adenocarcinoma (OAC). However, its role in regulating radiosensitivity and genomic instability is unknown. We developed an isogenic model of radioresistance in OAC called OE33R....

Expression profiles of cohesins, shugoshins and spindle assembly checkpoint genes in rhesus macaque oocytes predict their susceptibility for aneuploidy during embryonic development

High frequencies of chromosomal anomalies are reported in human and non-human primate in vitro-produced preimplantation embryos. It is unclear why certain embryos develop aneuploidies while others remain euploid. A differential susceptibility to aneuploidy is most likely a consequence of events that occur before oocyte collection. One hypothesis is that the relative transcript levels of cohesins, shugoshins and spindle assembly checkpoint genes are correlated with the occurrence of chromosomal anomalies. Transcript levels of these genes were quantified in individual oocytes that were either mature (group 1, low aneuploidy rate) or immature (group 2, high aneuploidy rate) at retrieval, utilizing TaqMan-based real-time PCR. The transcript level in each oocyte was categorized as absent, below the median or above the median in order to conduct comparisons. Statistically significant differences were observed between group 1 and group 2 for SGOL1 and BUB1. There were more oocytes with SGOL1 expression levels above the median in group 1, while oocytes lacking BUB1 were only observed in group 1. These findings suggest that higher SGOL1 levels in group 1 oocytes could better protect against a premature separation of sister chromatids than in embryos derived from group 2 oocytes. The absence of BUB1 transcripts in group 1 was frequently associated with reduced expression of either mitotic cohesins or shugoshins. We hypothesize that ablation of BUB1 could induce mitotic arrest in oocytes that fail to express a complete complement of cohesins and shugoshins, thereby reducing the number of developing aneuploid preimplantation embryos.

Evidence that the spindle assembly checkpoint does not regulate APCFzyactivity inDrosophilafemale meiosis

The spindle assembly checkpoint (SAC) plays an important role in mitotic cells to sense improper chromosome attachment to spindle microtubules and to inhibit APC(Fzy)-dependent destruction of cyclin B and Securin; consequent initiation of anaphase until correct attachments are made. In Drosophila , SAC genes have been found to play a role in ensuring proper chromosome segregation in meiosis, possibly reflecting a similar role for the SAC in APC(Fzy) inhibition during meiosis. We found that loss of function mutations in SAC genes, Mad2, zwilch, and mps1, do not lead to the predicted rise in APC(Fzy)-dependent degradation of cyclin B either globally throughout the egg or locally on the meiotic spindle. Further, the SAC is not responsible for the inability of APC(Fzy) to target cyclin B and promote anaphase in metaphase II arrested eggs from cort mutant females. Our findings support the argument that SAC proteins play checkpoint independent roles in Drosophila female meiosis and that other mechanisms must function to control APC activity.

The Accuracy of Survival Time Prediction for Patients with Glioma Is Improved by Measuring Mitotic Spindle Checkpoint Gene Expression

Identification of gene expression changes that improve prediction of survival time across all glioma grades would be clinically useful. Four Affymetrix GeneChip datasets from the literature, containing data from 771 glioma samples representing all WHO grades and eight normal brain samples, were used in an ANOVA model to screen for transcript changes that correlated with grade. Observations were confirmed and extended using qPCR assays on RNA derived from 38 additional glioma samples and eight normal samples for which survival data were available. RNA levels of eight major mitotic spindle assembly checkpoint (SAC) genes (BUB1, BUB1B, BUB3, CENPE, MAD1L1, MAD2L1, CDC20, TTK) significantly correlated with glioma grade and six also significantly correlated with survival time. In particular, the level of BUB1B expression was highly correlated with survival time (p<0.0001), and significantly outperformed all other measured parameters, including two standards; WHO grade and MIB-1 (Ki-67) labeling index. Measurement of the expression levels of a small set of SAC genes may complement histological grade and other clinical parameters for predicting survival time.