Aneuploid Condition Research Articles

Congenital Aneuploidy in Klinefelter Syndrome with B-Cell Acute Lymphoblastic Leukemia Might Be Associated with Chromosomal Instability and Reduced Telomere Length.

Simple SummaryKlinefelter syndrome (KS) is a rare congenital aneuploidy characterized by inherited gain of one X chromosome (XXY). KS is associated with higher susceptibility to the development of cancer. Somatic acquired chromosomal aberrations and chromosomal instability are hallmarks of cancer and leukemia but little is known about the cellular mechanisms involved. The conducted research aimed to identify genomic mechanisms involved in chromosomal evolution mechanisms important for leukemic development. In the leukemic blasts of a patient with KS and B-cell acute lymphoblastic leukemia (B-ALL), we identified additional acquired chromosomal aberration and a significant reduction in the length of the chromosomal ends, i.e., telomeres. A literature review of KS patients with B-ALL revealed that the majority of these patients had acquired two or more additional chromosomal aberrations at B-ALL diagnosis. These data indicate that enhanced reduction in telomere length might be associated with chromosomal instability and may serve as a future target for therapy or prevention.Rare congenital aneuploid conditions such as trisomy 13, trisomy 18, trisomy 21 and Klinefelter syndrome (KS, 47,XXY) are associated with higher susceptibility to developing cancer compared with euploid genomes. Aneuploidy frequently co-exists with chromosomal instability, which can be viewed as a “vicious cycle” where aneuploidy potentiates chromosomal instability, leading to further karyotype diversity, and in turn, paving the adaptive evolution of cancer. However, the relationship between congenital aneuploidy per se and tumor initiation and/or progression is not well understood. We used G-banding analysis, array comparative genomic hybridization analysis and quantitative fluorescence in situ hybridization for telomere length analysis to characterize the leukemic blasts of a three-year-old boy with KS and B-cell acute lymphoblastic leukemia (B-ALL), to gain insight into genomic evolution mechanisms in congenital aneuploidy and leukemic development. We found chromosomal instability and a significant reduction in telomere length in leukemic blasts when compared with the non-leukemic aneuploid cells. Reviewing published cases with KS and B-ALL revealed 20 additional cases with B-ALL diagnostic cytogenetics. Including our present case, 67.7% (14/21) had acquired two or more additional chromosomal aberrations at B-ALL diagnosis. The presented data indicate that congenital aneuploidy in B-ALL might be associated with chromosomal instability, which may be fueled by enhanced telomere attrition.

Trisomy 21-associated increases in chromosomal instability are unmasked by comparing isogenic trisomic/disomic leukocytes from people with mosaic Down syndrome.

Down syndrome, which results from a trisomic imbalance for chromosome 21, has been associated with 80+ phenotypic traits. However, the cellular changes that arise in somatic cells due to this aneuploid condition are not fully understood. The primary aim of this study was to determine if germline trisomy 21 is associated with an increase in spontaneous somatic cell chromosomal instability frequencies (SCINF). To achieve this aim, we quantified SCINF in people with mosaic Down syndrome using a cytokinesis-blocked micronucleus assay. By comparing values in their isogenic trisomic/disomic cells, we obtained a measure of differences in SCINF that are directly attributable to a trisomy 21 imbalance, since differential effects attributable to “background” genetic factors and environmental exposures could be eliminated. A cross-sectional assessment of 69 people with mosaic Down syndrome (ages 1 to 44; mean age of 12.84 years) showed a significantly higher frequency of micronuclei in their trisomic (0.37 ± 0.35 [mean ± standard deviation]) compared to disomic cells (0.18 ± 0.11)(P <0.0001). The daughter binucleates also showed significantly higher levels of abnormal patterns in the trisomic (1.68 ± 1.21) compared to disomic (0.35 ± 0.45) cells (P <0.0001). Moreover, a significant Age x Cell Type interaction was noted (P = 0.0113), indicating the relationship between age and SCINF differed between the trisomic and disomic cells. Similarly, a longitudinal assessment (mean time interval of 3.9 years; range of 2 to 6 years) of 18 participants showed a mean 1.63-fold increase in SCINF within individuals over time for their trisomic cells (P = 0.0186), compared to a 1.13-fold change in their disomic cells (P = 0.0464). In summary, these results showed a trisomy 21-associated, age-related increase in SCINF. They also underscore the strength of the isogenic mosaic Down syndrome model system for “unmasking” cellular changes arising from a trisomy 21 imbalance.

Trisomy 21 impairs PGE2 production in dermal fibroblasts

The triplication of human chromosome 21 results in Down syndrome (DS), the most common genetic form of intellectual disability. This aneuploid condition also results in an enhanced risk of a spectrum of comorbid conditions, such as leukemia, early onset Alzheimer’s disease, and diabetes. Individuals with DS also display an increased incidence of wound healing complications and resistance to solid tumor development. Due to this unique phenotype and the involvement of eicosanoids in key comorbidities like poor healing and tumor development, we hypothesized that cells from DS individuals would display altered eicosanoid production. Using age- and sex-matched dermal fibroblasts we interrogated this hypothesis. Briefly, assessment of over 90 metabolites derived from cyclooxygenase (COX), lipoxygenase (LOX), and cytochrome p450 systems revealed a possible deficiency in the COX system. Basal gene expression and Western blotting experiments showed significantly decreased gene expression of COX1 and 2, and COX2 protein abundance in DS fibroblasts compared to euploid controls. Further, using two different stressors, scratch wound or LPS, we found that DS fibroblasts could not upregulate COX2 abundance and prostaglandin E2 production. Together, these findings show that dermal fibroblasts from DS individuals have a deficient COX2 response, which may contribute to wound healing complications and tumor resistance in DS.

Study on amniotic fluid metabolism in the second trimester of Trisomy 21.

BackgroundTrisomy 21 is a common aneuploid condition in humans and accounts for approximately one quarter of all aneuploid live births. To date, early diagnosis of Trisomy 21 remains a challenging task. Metabolomics may prove an innovative tool to study the early pathophysiology of Trisomy 21 at a functional level.MethodsUltra‐performance liquid chromatography coupled with mass spectrometer (UPLC‐MS) was used for untargeted metabolomic analysis of amniotic fluid samples from women having normal and trisomy 21 fetuses.ResultsMany significantly changed metabolites were identified between amniotic fluid samples from Trisomy 21 pregnancies and normal euploid pregnancies, such as generally lower levels of several steroid hormones and their derivatives, higher levels of glutathione catabolites coupled with lower levels of gamma‐glutamyl amino acids, and increased levels of phospholipid catabolites, sugars, and dicarboxylic acids. The identification of a human milk oligosaccharide in amniotic fluid may worth further investigation, since confirmation of this observation may have significant implications for regulation of fetal development.ConclusionsThe metabolisms in amniotic fluid from Trisomy 21 and normal pregnancies are quite different, and some of the significantly changed metabolites may be considered as candidates of early diagnostic biomarkers for Trisomy 21.

Advanced paternal age does not affect embryo aneuploidy following blastocyst biopsy in egg donor cycles

To study the impact of advanced paternal age on embryo aneuploidy. This is a multicenter international retrospective case series of couples undergoing assisted reproduction via in vitro fertilization using donor eggs to control for maternal factors and preimplantation genetic testing for aneuploidy via next-generation sequencing at Igenomix reproductive testing centers. The main outcome measure was the prevalence of embryo aneuploidy in egg donor cycles. Semen analysis data was retrieved for a small subset of the male patients. Data from 1202 IVF/ICSI egg donor cycles using ejaculated sperm (total 6934 embryos) evaluated using PGT-A between January 2016 and April 2018 in a global population across all Igenomix centers were included. No significant association was identified between advancing paternal age and the prevalence of embryo aneuploidy overall and when analyzing for each chromosome. There was also no significant association between advancing paternal age and specific aneuploid conditions (monosomy, trisomy, partial deletion/duplication) for all chromosomes in the genome. This is the largest study of its kind in an international patient population to evaluate the impact of advancing paternal age on embryo aneuploidy. We conclude there is no specific effect of paternal age on the prevalence of embryo aneuploidy in the context of embryo biopsies from egg donor cycles.

Aggressive Aneuploid Acute Myeloid Leukemia Is Dependent on Alterations of P53, Gain of APC and PLK1 and Loss of RAD50

Abstract Chromosome number alterations, aneuploidy, is a hallmark of cancer. It occurs in about 15% of acute myeloid leukemia (AML) cases, is generally preserved throughout disease progression (Bochtler et al. Leukemia 2015) and correlates with adverse prognosis (Breems et al. JCO 2008, Papaemmanuil et al. NEJM 2016). This evidence highlights the need of understanding the molecular mechanisms that promote and sustain aneuploidy in AML, in order to define novel potential therapeutic targets. In the NGS-PTL project we profiled the genomic landscape of 536 hematological samples by whole exome sequencing (WES, Illumina). Among them, we analyzed 88 and 68 samples from aneuploid (A-) FLT3-wildtype AML (isolated trisomy and monosomy, complex and monosomal karyotype) and euploid (E-) AML (normal and complex karyotype, &lt;3 abnormalities), respectively (100 bp, paired-end). Variants were called by MuTect and Varscan 2.0. WES output was integrated with genotype data (CytoScan HD Array, Affymetrix and Nexus Copy Number analysis) and gene expression profiling (HTA 2.0 and TAC 3.0, Affymetrix). A-AML showed an increased genomic instability, as confirmed by a higher mutation load compared with E-AML (median number of variants: 22 (range: 2-95) and 11 (range: 3-45), respectively, p&lt;.001), which was associated with increased patients' age (median age of 62 for A-AML and 55 for E-AML, p&lt;.05). The increased age and mutation load correlated with a mutational signature with prominence of C&gt;A substitutions, compared with the C&gt;T transition-related signature, which is prevalent in AML. A-AML was associated with mutations and/or heterozygous deletion of TP53 (p&lt;.001), which co-occurred with copy number loss of both the tumor suppressor APC and the DNA repair gene RAD50 in 93% of cases (p&lt;.001). Moreover, A-AML was enriched for a gene expression signature of p53-deficiency, independently of TP53 structural defects (p&lt;.05, GSEA). Mutations and deregulated expression of genes involved in cell cycle contributed to the A-AML phenotype, with 68% A-AML vs. 32% E-AML patients (p&lt;.01) carrying at least one genomic lesion affecting the process. The alterations targeted the following pathways: DNA repair (i.e. reduced RAD50 expression, p&lt;.001), cell cycle checkpoints (i.e. mutated CHK2), regulation of PLK1 activity at G2/M transition (i.e. mutation and 2-fold upregulation of PLK1, p&lt;.01), mitotic metaphase and anaphase (i.e. increased CDC20 level, p&lt;.001) and separation of sister chromatids (i.e. mutated BUB1B, ESPL1, CENPO). Of note, a 3-gene signature composed of PLK1, CDC20 and RAD50, was able to discriminate 73% of patients between the A- and E-AML cohorts. This signature was confirmed at protein level. In parallel, E-AML showed a preferential dependency on epigenetic mechanisms, with recurrent genomic lesions of ASXL1/2, BCOR/L1, EZH2 and MLL, enrichment of FLT3 alterations and mutations activating RAS signal transduction (p&lt;.05). Of note, a HOX-related signature characterized by overexpression of the HOX family members HOXA7, HOXB3 and MEIS1 identified E-AML. We show here for the first time the molecular mechanisms promoting and maintaining aneuploidy in AML. Our results indicate that p53 deficiency, either caused by somatic mutations, copy number loss, impaired DNA damage response and enhanced PLK1 signaling synergize with APCgain, RAD50 structural or functional loss and forced progression through mitosis, to override cell cycle and mitotic checkpoints and allow the formation of daughter cells with an aberrant chromosome number. These mechanisms cooperate with recurrent mutations of genes involved in protein ubiquitination and proteasome-mediated protein catabolic process in A-AML, indicative of the attempt of aneuploid cells to override the proteotoxic stress due to the unbalanced protein load generated by the aneuploid condition. This evidence provides the rationale for exploiting proteasome inhibition (Velcade), p53 reactivation (MDM2/4 inhibitor) and targeting of the cell cycle (CHK1/2 inhibitor) downstream to p53 (WEE1 inhibitor) as strategies for novel combination therapies against aggressive aneuploid AML, which are under clinical investigation in our Institution and may serve as a model for aneuploid tumors. GS and AP: equal contribution. Supported by: FP7 NGS-PTL project, ELN, AIL, AIRC, PRIN, progetto Regione-Università 2010-12 (L. Bolondi). Disclosures Haferlach: MLL Munich Leukemia Laboratory: Employment, Equity Ownership. Martinelli:Ariad: Consultancy, Speakers Bureau; MSD: Consultancy; Celgene: Consultancy, Speakers Bureau; Roche: Consultancy, Speakers Bureau; Genentech: Consultancy; Novartis: Speakers Bureau; BMS: Speakers Bureau; Pfizer: Consultancy, Speakers Bureau; Amgen: Consultancy, Speakers Bureau.

Dissecting the Molecular Mechanisms of Aneuploidy in Acute Myeloid Leukemia By Next Generation Sequencing

Acute Myeloid Leukemia (AML) is a heterogeneous malignancy characterized by the expansion of myeloid precursor cells with limited or abnormal differentiation capacity. A relatively common event in AML is represented by chromosome gain or loss. Numerical chromosome abnormalities, which define aneuploidy, have a detrimental effect in primary non-malignant cells, since they dramatically reduce cellular fitness. However, evidence suggests that they have a causative role in tumorigenesis and are well tolerated in transformed cells belonging to the myeloid lineage.Aim of the study is to elucidate the pathogenic mechanisms causing and sustaining aneuploidy in AML in order to find novel potential therapeutic targets.A panel of genetic alterations was analyzed on 886 AML cases at Seràgnoli Institute in Bologna between 2002 and 2013. Among them, 31 samples were subjected to whole exome sequencing (WES, Illumina Hiseq2000). Raw data were processed with WES Pipeline web tool for variants detection. Gene expression profiling (GEP, Affymetrix) was performed on bone marrow cells from 49 AML patients at diagnosis with more than 80% blast cells, including 22 aneuploid cases (carrying monosomy, trisomy or a monosomal karyotype) and 27 cases with normal karyotype. The aneuploid status was confirmed by single nucleotide polymorphism (SNP) array.WES analysis of 13 aneuploid and 12 euploid AML cases revealed a significantly higher median value of genetic variants and mutated genes in aneuploid compared with euploid samples (aneuploid vs. euploid: median of variants, 30 vs. 20 (p=0.02) including nonsynonimous single nucleotide variants, frameshift insertions and deletions, stopgains; median of mutated genes, 25 vs. 17 (p=0.05); details will be presented at the meeting). Noticeably, by gene ontology analysis of mutated genes in the aneuploid cohort we observed a strong enrichment in genes regulating cell cycle, including chromosome organization (p=5.4x10-4) and mitotic sister chromatid cohesion (p=6.98x10-4), and chromatin modification (p=1.3x10-4), with most of the variants being not annotated in the COSMIC database. Euploid samples were enriched for mutations affecting genes involved in cytoskeleton (p=1.6x10-3) and metabolic activities (p=1.9x10-3). A number of genes mutated in the aneuploid cases belong to the APCCdc20 complex and localize on chromosomes generally spared by aneuploidy, supporting the key role of the identified aberrations in the molecular mechanisms leading to numerical chromosome abnormalities. Among several mutations predicted as “drivers” by DOTS-Finder tool (CCDC144NL, DNMT3A, GXYLT1, MESP1, TPRX1,TPTE, ZNF717), we defined some candidates involved in cell cycle regulation and DNA replication. Functional analysis are ongoing. Furthermore, a tumor suppressor function was associated with mutated genes involved in the DNA repair process. In our WES analysis, we identified a subgroup of genes linked to DNA damage response, including TP53, which are preferentially mutated in the aneuploid cohort. Since P53 is a limiting-factor in aneuploidy-induced tumorigenesis, we analyzed the mutational status in a larger cohort of AML patients by Next Generation sequencing (NGS) and Sanger sequencing. Interestingly, we identified TP53 mutations in 15/58 aneuploid vs. 1/36 euploid cases (p=3.8x10-3). Finally, differential expression of genes involved in DNA damage and integrity checkpoints was identified by GEP of aneuploid and euploid AML samples.Previous evidence showed that loss of the spindle checkpoint gene BUB1B induces aneuploidy and predisposes to tumorigenesis. Our data, obtained by integrated NGS and GEP approaches, support a causal link between mutations in a panel of genes involved in cell cycle control/chromosome organization and aneuploidy in AML. Genetic and transcriptional alterations of genes regulating DNA damage response were detected in our AML cohort, suggesting novel molecular mechanisms for the acquisition and/or maintenance of the aneuploid condition and consequently, of leukemogenesis. The results indicate that the identified genomic aberrations likely drive chromosome gain and/or loss in AML by cooperating with alterations affecting different pathways, in order to overcome the unfitness barrier induced by aneuploidy.Supported by: FP7 NGS-PTL project, ELN, AIL, AIRC, PRIN, progetto Regione-Università 2010-12 (L. Bolondi). DisclosuresMartinelli:Novartis: Consultancy, Speakers Bureau; BMS: Consultancy, Speakers Bureau; Pfizer: Consultancy; ARIAD: Consultancy.

Abstract 2243: Gene expression signature of aneuploidy in acute myeloid leukemia

Abstract Acute Myeloid Leukemia (AML) is a heterogeneous malignancy characterized by the expansion of myeloid precursor cells with limited or abnormal differentiation capacity. A relatively common event in AML is represented by chromosome gain or loss. Numerical chromosome abnormalities, which define the aneuploid condition, have a detrimental effect in primary non-malignant cells, since they dramatically reduce cellular fitness. However evidence suggests that they have a causative role in tumorigenesis and that they are well tolerated in transformed cells belonging to the myeloid lineage. Aim of the study is to elucidate the pathogenic mechanisms that sustain and contribute to aneuploidy in AML. We have performed gene expression profile (GEP) analysis of bone marrow cells from 42 AML patients, including 19 aneuploid cases and 23 cases with normal karyotype. All samples contained more than 80% blast cells. The aneuploid cohort included AML cases carrying one (or more) monosomy, trisomy or a monosomal karyotype. Our analysis covered more than 245,000 and 40,000 coding and non-coding transcripts, respectively (the latter comprising microRNAs), and a significant number of exon-exon junctions, which allow the analysis of multiple splicing isoforms. Quality controls confirmed that the data show comparable signal values. The gene expression signature of aneuploid samples have been compared to normal karyotype ones. We have identified a set of coding and non-coding transcripts which are differentially expressed between the two groups (p≤0.05, including more than 20 genes with a fold difference ≥2) and defined a gene signature that allows the discrimination between aneuploid and euploid samples in our dataset. The analysis of an increased number of cases will confirm the results and allow the sub-stratification of aneuploid samples according to their GEP. Our data will be further validated by comparing them with published GEP datasets and the gene signature will be characterized by pathway analysis. This study provides novel insights into the molecular mechanism that sustain aneuploidy in AML. The biological validation of genes which are commonly and specifically deregulated in aneuploid AML patients will guide the design of future therapeutic strategies targeting key players in the disease. Acknowledgements: European LeukemiaNet, AIRC, AIL, Prin 2010-2011, FP7 NGS-PTL project. Citation Format: Giorgia Simonetti, Antonella Padella, Viviana Guadagnuolo, Cristina Papayannidis, Francesca Volpato, Emanuela Ottaviani, Serena Formica, Annalisa Astolfi, Ilaria Iacobucci, Giovanni Capranico, Daniel Remondini, Giovanni Martinelli. Gene expression signature of aneuploidy in acute myeloid leukemia. [abstract]. In: Proceedings of the 105th Annual Meeting of the American Association for Cancer Research; 2014 Apr 5-9; San Diego, CA. Philadelphia (PA): AACR; Cancer Res 2014;74(19 Suppl):Abstract nr 2243. doi:10.1158/1538-7445.AM2014-2243

RNF212 is a dosage-sensitive regulator of crossing-over during mammalian meiosis

Crossing-over ensures accurate chromosome segregation during meiosis, and every pair of chromosomes obtains at least one crossover, even though the majority of recombination sites yield non-crossovers. A putative regulator of crossing-over is RNF212, which is associated with variation in crossover rates in humans. We show that mouse RNF212 is essential for crossing-over, functioning to couple chromosome synapsis to the formation of crossover-specific recombination complexes. Selective localization of RNF212 to a subset of recombination sites is shown to be a key early step in the crossover designation process. RNF212 acts at these sites to stabilize meiosis-specific recombination factors, including the MutSγ complex (MSH4-MSH5). We infer that selective stabilization of key recombination proteins is a fundamental feature of meiotic crossover control. Haploinsufficiency indicates that RNF212 is a limiting factor for crossover control and raises the possibility that human alleles may alter the amount or stability of RNF212 and be risk factors for aneuploid conditions.

Sexual differentiation in the developing mouse brain: contributions of sex chromosome genes

Neural sexual differentiation begins during embryogenesis and continues after birth for a variable amount of time depending on the species and brain region. Because gonadal hormones were the first factors identified in neural sexual differentiation, their role in this process has eclipsed investigation of other factors. Here, we use a mouse with a spontaneous translocation that produces four different unique sets of sex chromosomes. Each genotype has one normal X-chromosome and a unique second sex chromosome creating the following genotypes: XY(*x) , XX, XY(*) , XX(Y) (*) . This Y(*) mouse line is used by several laboratories to study two human aneuploid conditions: Turner and Klinefelter syndromes. As sex chromosome number affects behavior and brain morphology, we surveyed brain gene expression at embryonic days 11.5 and 18.5 to isolate X-chromosome dose effects in the developing brain as possible mechanistic changes underlying the phenotypes. We compared gene expression differences between gonadal males and females as well as individuals with one vs. two X-chromosomes. We present data showing, in addition to genes reported to escape X-inactivation, a number of autosomal genes are differentially expressed between the sexes and in mice with different numbers of X-chromosomes. Based on our results, we can now identify the genes present in the region around the chromosomal break point that produces the Y(*) model. Our results also indicate an interaction between gonadal development and sex chromosome number that could further elucidate the role of sex chromosome genes and hormones in the sexual differentiation of behavior.

Chromosomal instability and aneuploidy in cancer: from yeast to man

Aneuploidy is frequently associated with disease and developmental abnormalities. It is also a key characteristic of cancer. Several model systems have been developed to study the role of chromosomal instability and aneuploidy in tumorigenesis. The results are surprisingly complex, with the conditions sometimes promoting and sometimes inhibiting tumour formation. Here, we review the effects of aneuploidy and chromosomal instability in cells and model systems of cancer, propose a model that could explain these complex findings and discuss how the aneuploid condition could be exploited in cancer therapy.

Learning from your mistakes: is aneuploidy so bad, after all?

Learning from your mistakes: is aneuploidy so bad, after all?

Core Concepts: Chromosome Aneuploidies

Aneuploidy, or deviation from the diploid human chromosome complement of 46, may have physical effects ranging from mild or undetectable, as in a male infant with 47 chromosomes including an additional Y chromosome, to severe, as occurs in infants with an additional chromosome 13 or 18. We discuss the autosomal (13, 18, and 21) and sex chromosome (X, Y) aneuploidies that can be expected in the neonatal health care setting, including clinical signs and symptoms that may be indications for further study. We review appropriate diagnostic testing including chromosome, fluorescent in situ hybridization, and microarray comparative genomic hybridization studies, indicating where parental follow-up studies are necessary to provide accurate recurrence risk counseling. For each aneuploid condition that is likely to be encountered in a living infant, we review appropriate clinical management strategies. Suggested readings and family resources are provided for the aneuploidies that are commonly observed in the newborn, and the reader is directed to additional resources for partial aneuploidies, which are beyond the scope of this review.

031. THE ORIGIN OF ANEUPLOIDY IN HUMANS: WHERE WE'VE BEEN, WHERE WE'RE GOING

With the advent of the human genome project in the 1990s, DNA markers became available, allowing us to determine the parent and meiotic stage of origin of human aneuploid conditions. This approach has been extensively used to study the origin of trisomies, with one over-arching conclusion: the vast majority of trisomies derive from errors in the development of the egg and, in particular, from nondisjunction occurring in the first maternal meiotic division (MI). However, against this general background, it has also become apparent that there is considerable chromosome-to-chromosome variation. For example, certain aneuploidies (e.g., the XXY condition, or Klinefelter syndrome) are commonly paternal in origin, while others (e.g., trisomy 16, the most common human trisomy) almost always originate from maternal MI errors. Thus, we now know that individual chromosomes behave differently with respect to mechanisms of meiotic nondisjunction. In this presentation, we will summarize results of these parental origin studies of aneuploidy and discuss the involvement of the first identified molecular correlate of nondisjunction – aberrant meiotic recombination – in the genesis of these abnormalities. We will also look forward, discussing the development of mouse models of human aneuploidy, and recent advances in molecular cytogenetics that make it possible to directly analyze human meiosis ‘as it happens’ in fetal oocytes and in spermatocytes.

Expression of LFA-1 by a lymphoblastoid cell line from a patient with monosomy 21: effects on intercellular adhesion

Monosomy 21 (M21) is a rare aneuploid condition which in certain cases leads to reduced levels of chromosome 21 gene products. We have prepared an Epstein-Barr virus lymphoblastoid cell-line (LCL) from patient with M21 who has immunological abnormalities, and analysed the expression of lymphocyte function-associated antigen-1 (LFA-1). This heterodimeric leucocyte integrin consists of CD11a (alpha) subunits non-covalently associated with CD18 (beta) subunits coded, respectively, by genes on chromosomes 16 and 21. To determine whether monosomy 21 results in decreased expression of LFA-1, monoclonal antibodies were used to compare the expression of CD11a and CD18 on the M21 LCL with LCL from trisomy 21 (Down's syndrome, T21), normal controls and a possible case of leucocyte adhesion deficiency. In addition, phorbol-ester-induced homotypic adhesion, an LFA-1-mediated effect, was compared in these LCLs. The results are consistent with a gene dosage mediated reduction of LFA-1 expression by the M21 LCL.

Profiling expression changes caused by a segmental aneuploid in maize

BackgroundWhile changes in chromosome number that result in aneuploidy are associated with phenotypic consequences such as Down syndrome and cancer, the molecular causes of specific phenotypes and genome-wide expression changes that occur in aneuploids are still being elucidated.ResultsWe employed a segmental aneuploid condition in maize to study phenotypic and gene expression changes associated with aneuploidy. Maize plants that are trisomic for 90% of the short arm of chromosome 5 and monosomic for a small distal portion of the short arm of chromosome 6 exhibited a phenotypic syndrome that includes reduced stature, tassel morphology changes and the presence of knots on the leaves. The knotted-like homeobox gene knox10, which is located on the short arm of chromosome 5, was shown to be ectopically expressed in developing leaves of the aneuploid plants. Expression profiling revealed that ~40% of the expressed genes in the trisomic region exhibited the expected 1.5 fold increased transcript levels while the remaining 60% of genes did not show altered expression even with increased gene dosage.ConclusionWe found that the majority of genes with altered expression levels were located within the chromosomal regions affected by the segmental aneuploidy and exhibits dosage-dependent expression changes. A small number of genes exhibit higher levels of expression change not predicted by the dosage, or display altered expression even though they are not located in the aneuploid regions.

First-Trimester Ultrasound Assessment of the Nasal Bone to Screen for Aneuploidy

Increasingly, women are choosing first-trimester risk assessment for Down syndrome and other aneuploid conditions. Recent studies have suggested that adding ultrasound assessment of the nasal bone to nuchal translucency thickness and maternal serum analytes in the first trimester will improve performance. This report assesses the current literature and discusses practical issues that must be addressed before widespread implementation of nasal bone screening in the United States.

The origin of human aneuploidy: where we have been, where we are going

Aneuploidy is the most common chromosome abnormality in humans, and is the leading genetic cause of miscarriage and congenital birth defects. Since the identification of the first human aneuploid conditions nearly a half-century ago, a great deal of information has accrued on its origin and etiology. We know that most aneuploidy derives from errors in maternal meiosis I, that maternal age is a risk factor for most, if not all, human trisomies, and that alterations in recombination are an important contributor to meiotic non-disjunction. In this review, we summarize some of the data that have led to these conclusions, and discuss some of the approaches now being used to address the underlying causes of meiotic non-disjunction in humans.

Sperm and Blastomere Aneuploidy Detection in Reproductive Genetics and Medicine

The use of multiple probes in fluorescence in situ hybridization (FISH) permits the simultaneous analysis of several chromosomes in both blastomeres and spermatozoa. Preimplantation genetic diagnosis (PGD) for aneuploidy provides information on embryonic chromosomal status, enabling the selection of embryos carrying aneuploid condition. This strategy directly affects implantation, as documented for patients with a poor prognosis for pregnancy, who have the tendency to generate high proportions of chromosomally abnormal embryos. PGD for aneuploidy also has contributed information on early phases in human embryology by clarifying the molecular basis in some cases of irregular development. Multicolor FISH has also been used to study chromosomes on spermatozoa. Experimental strategies and modifications enabled the analysis of samples with a very low number of sperm cells, including samples retrieved from the genital tract or directly from the testicular tissue. The results confirmed that the incidence of aneuploidy increases proportionally with the severity of the male-factor condition. This observation suggests that, in selected cases, the paternal contribution to aneuploidy in the developing conceptus could be more relevant than expected from general data from aborted fetuses and live births.

Differential chromosome control of ploidy in the yeastSaccharomyces cerevisiae

In Saccharomyces cerevisiae, aneuploidy is well tolerated and stable. We analysed whether the induced loss of a disomic chromosome favours endo-reduplication of the remaining chromosome or the cells prefer to retain the acquired euploidy. Chromosome VIII disomes and trisomes were tagged with GFP (green fluorescent protein), DsRed (red fluorescent protein) and BFP (blue fluorescent protein) integrated at the thr1 locus, using our newly designed STIK (specific targeted integration of kanamycin resistance-associated, non-selectable DNA) plasmid system. A knockout cassette for centromere 8 was constructed with the hygromycin-B marker, which was transformed into the strains. The transformants lost sensitivity to hygromycin, thereby indicating the event of centromere replacement. Quantitative PCR and Southern analysis were performed for chromosome VIII copy number determination by probing the markers located on both the right (ARG4 and THR1) and left (GUT1) arm whereas, for chromosome V, markers such as HIS1, located on right arm, and URA3, on left arm, were used. The loss of an extranumerary chromosome VIII in a disome and trisome leads to stable euploidy. Furthermore, in a wild-type diploid, deletion of a copy of chromosome VIII, leads to monosomy, and restoration of euploidy after 22 generations, by reduplication of chromosome VIII, and consequent loss of heterozygosis (LOH). However, chromosome V knockouts in chromosome VIII trisome, still showed LOH and duplication of chromosome V, with return to the original aneuploid condition. These results suggest that yeast cells could control the integrity of their genetic complement acting at the individual chromosome level.