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PubMed2006

Parental and chromosomal origin of unbalanced de novo structural chromosome abnormalities in man.

We report the parental origin, and where possible the chromosomal origin of 115 de novo unbalanced structural chromosome abnormalities detectable by light microscopy. These consisted of 39 terminal deletions, 35 interstitial deletions, 8 rings, 12 duplications and 21 unbalanced translocations. In all categories the majority of abnormalities were of paternal origin, although the proportions varied from a high of 84% in the interstitial deletions and rings to a low of 58% in the duplications. Among the interstitial deletions and duplications, there were approximately equal numbers of intra- and interchromosomal abnormalities, while the majority of unbalanced translocations were isodisomic for the duplicated chromosome. The examination of the parental ages in the four main classes of abnormality showed terminal deletions of maternal origin to be associated with a significantly reduced maternal age. Thus, there is a clear propensity for structural chromosome abnormalities to occur in male germ cells, although the chromosomal origin seems similar irrespective of the parental origin.

Chromosome Aberrations↗

PubMed2000

Interchromosomal effects for chromosome 21 in carriers of structural chromosome reorganizations determined by fluorescence in situ hybridization on sperm nuclei.

We have used dual color fluorescence in situ hybridization (FISH) on decondensed sperm heads from four carriers of structural chromosome reorganizations, viz. t(3;15), t(Y;7), t(13;22) and inv(9), to assess the possible existence of an interchromosomal effect (ICE) on the segregation of chromosome 21. In the carriers of t(Y;7), t(13;22) and inv(9), all results were within the limits described in controls. A highly significant increase (P<0.0001) of disomy 21 (1.90% v 0.37%), which could be considered as a positive ICE, was observed in the t(3;15) carrier. Significantly higher percentages (P<0.0001) of diploid sperm (5.71% v. 0.27%) were also observed in this patient. Our results suggests that the occurrence of an ICE may depend on the reorganization and on the chromosome and chromosome regions involved, resulting in a particular meiotic behaviour (presence of unsynapsed regions, preferential meiotic configurations) that could lead to the observed increase in chromosome 21 disomies. Further studies with this technical approach in a wide range of structural reorganizations could help to elucidate the actual occurrence of ICEs.

Adult↗

PubMed1996

Cytogenetic and genetic studies of radiation-induced chromosome damage in mouse oocytes. I. Numerical and structural chromosome anomalies in metaphase II oocytes, pre- and post-implantation embryos.

The incidences of X-ray induced numerical and structural chromosome anomalies were screened in a range of developmental stages from metaphase II oocytes through to post-implantation embryos. Following 1 Gy of acute X-rays to immediately preovulatory stage oocytes, the rate of hyperploidy (chromosome gain) was found to be elevated over levels in unirradiated controls, at metaphase II, in 1-cell and 3.5 day pre-implantation embryos but not in 8.5 day post-implantation foetuses. In the latter, however, the frequency of mosiacism was significantly increased. A similar response of an increase in mosaicism but not in hyperploidy in 8.5 day post-implantation embryos was also found after irradiation of dictyate stage oocytes with 4 Gy of acute X-rays. Significantly elevated frequencies of structural chromosome anomalies were present in metaphase II oocytes and pre-implantation embryonic stages, but could not be detected in block-stained chromosome preparations from 8.5 day post-implantation foetuses. However, analysis of chromosome preparations after G-banding showed that almost 14% of 14.5 day foetuses carried a chromosome rearrangement after 1 Gy of X-rays to immediately preovulatory stage oocytes. Overall, our data indicate that the presence of radiation-induced chromosome gains are incompatible with embryonic survival but that a proportion of embryos with structural chromosome damage develop past mid-gestation. These latter embryos are therefore potentially capable of contributing to the genetic burden of the next generation.

Animals↗

PubMed1998

SMC proteins and chromosome structure.

The structure of chromosomes is largely determined by chromosome-associated proteins. Members of the SMC (structural maintenance of chromosomes) family play an important role in both prokaryotic and eukaryotic chromosome structure and dynamics. SMC proteins are involved in chromosome condensation, sister-chromatid cohesion, sex-chromosome dosage compensation, genetic recombination and DNA repair. There have been major advances recently in understanding the function of SMC proteins--including the identification of biochemical activities of SMC-containing protein complexes and the realization that individual SMC proteins might link seemingly unrelated aspects of chromosomal metabolism.

Animals↗

PubMed2004

Structural chromosomal mosaicism and prenatal diagnosis.

True structural chromosomal mosaicism are rare events in prenatal cytogenetics practice and may lead to diagnostic and prognostic problems. Here is described the case of a fetus carrying an abnormal chromosome 15 made of a whole chromosome 2p translocated on its short arm in 10% of the cells, in association with a normal cell line. The fetal karyotype was 46,XX,add(15)(p10).ish t(2;15)(p10;q10)(WCP2+)[3]/46,XX[27]. Pregnancy was terminated and fetus examination revealed a growth retardation associated with a dysmorphism including dolichocephaly, hypertelorism, high forehead, low-set ears with prominent anthelix and a small nose, which were characteristic of partial trisomy 2p. Possible aetiologies for prenatal mosaicism involving a chromosomal structural abnormality are discussed.

Abnormalities, Multiple↗

PubMed1986

A twin study of structural chromosome aberrations in lymphocytes.

Structural chromosome aberrations were analyzed in peripheral lymphocytes of eight monozygotic (MZ) and seven dizygotic (DZ) pairs of male twins. There was no significant intrapair difference in the variance of aberration frequencies among the MZ and DZ twins. Thus, there was no evidence of a major genetic influence on the development of structural chromosome aberrations. Although a genetic component could not be excluded, it was concluded that any chromosome aberrations observed were probably due mainly to environmental influences.

Adult↗

PubMed2004

Visualization of early chromosome condensation: a hierarchical folding, axial glue model of chromosome structure.

Current models of mitotic chromosome structure are based largely on the examination of maximally condensed metaphase chromosomes. Here, we test these models by correlating the distribution of two scaffold components with the appearance of prophase chromosome folding intermediates. We confirm an axial distribution of topoisomerase IIalpha and the condensin subunit, structural maintenance of chromosomes 2 (SMC2), in unextracted metaphase chromosomes, with SMC2 localizing to a 150-200-nm-diameter central core. In contrast to predictions of radial loop/scaffold models, this axial distribution does not appear until late prophase, after formation of uniformly condensed middle prophase chromosomes. Instead, SMC2 associates throughout early and middle prophase chromatids, frequently forming foci over the chromosome exterior. Early prophase condensation occurs through folding of large-scale chromatin fibers into condensed masses. These resolve into linear, 200-300-nm-diameter middle prophase chromatids that double in diameter by late prophase. We propose a unified model of chromosome structure in which hierarchical levels of chromatin folding are stabilized late in mitosis by an axial "glue."

Adenosine Triphosphatases↗

PubMed2005

Large-scale genomic correlations in Arabidopsis thaliana relate to chromosomal structure.

BACKGROUND: The chromosomes of the plant Arabidopsis thaliana contain various genomic elements, distributed with appreciable spatial heterogeneity. Clustering of and/or correlations between these elements presumably should reflect underlying functional or structural factors. We studied the positional density fluctuations and correlations between genes, indels, single nucleotide polymorphisms (SNPs), retrotransposons, 180 bp tandem repeats, and conserved centromeric sequences (CCSs) in Arabidopsis in order to elucidate any patterns and possible responsible factors for their genomic distributions. RESULTS: The spatial distributions of all these elements obeyed a common pattern: the density profiles of each element within chromosomes exhibited low-frequency fluctuations indicative of regional clustering, and the individual density profiles tended to correlate with each other at large measurement scales. This pattern could be attributed to the influence of major chromosomal structures, such as centromeres. At smaller scales the correlations tended to weaken -- evidence that localized cis-interactions between the different elements had a comparatively minor, if any, influence on their placement. CONCLUSION: The conventional notion that retrotransposon insertion sites are strongly influenced by cis-interactions was not supported by these observations. Moreover, we would propose that large-scale chromosomal structure has a dominant influence on the intrachromosomal distributions of genomic elements, and provides for an additional shared hierarchy of genomic organization within Arabidopsis.

Arabidopsis↗

PubMed2001

A model for chromosome structure during the mitotic and meiotic cell cycles.

The chromosome scaffold model in which loops of chromatin are attached to a central, coiled chromosome core (scaffold) is the current paradigm for chromosome structure. Here we present a modified version of the chromosome scaffold model to describe chromosome structure and behavior through the mitotic and meiotic cell cycles. We suggest that a salient feature of chromosome structure is established during DNA replication when sister loops of DNA extend in opposite directions from replication sites on nuclear matrix strands. This orientation is maintained into prophase when the nuclear matrix strand is converted into two closely associated sister chromatid cores with sister DNA loops extending in opposite directions. We propose that chromatid cores are contractile and show, using a physical model, that contraction of cores during late prophase can result in coiled chromatids. Coiling accounts for the majority of chromosome shortening that is needed to separate sister chromatids within the confines of a cell. In early prophase I of meiosis, the orientation of sister DNA loops in opposite directions from axial elements assures that DNA loops interact preferentially with homologous DNA loops rather than with sister DNA loops. In this context, we propose a bar code model for homologous presynaptic chromosome alignment that involves weak paranemic interactions of homologous DNA loops. Opposite orientation of sister loops also suppresses crossing over between sister chromatids in favor of crossing over between homologous non-sister chromatids. After crossing over is completed in pachytene and the synaptonemal complex breaks down in early diplotene (= diffuse stage), new contractile cores are laid down along each chromatid. These chromatid cores are comparable to the chromatid cores in mitotic prophase chromosomes. As an aside, we propose that leptotene through early diplotene represent the 'missing' G2 period of the premeiotic interphase. The new chromosome cores, along with sister chromatid cohesion, stabilize chiasmata. Contraction of cores in late diplotene causes chromosomes to coil in a configuration that encourages subsequent syntelic orientation of sister kinetochores and amphitelic orientation of homologous kinetochore pairs on the spindle at metaphase I.

Chromosomes↗

PubMed2006

Mitotic chromosome structure and condensation.

Mitotic chromosome structure has been the cell biology equivalent of a 'riddle, wrapped in a mystery, inside an enigma'. Observations that genetic knockout or knockdown of condensin subunits or topoisomerase II cause only minimal perturbation in overall chromosome condensation, together with analysis of early stages of chromosome condensation and effects produced by histone H1 depletion, suggest a need to reconsider textbook models of mitotic chromosome condensation and organization.

Adenosine Triphosphatases↗

PubMed1990

[Consequences of abnormalities of chromosome structure in domestic animals].

Abnormalities in chromosome structure generally have no phenotypic expression but are very often associated with reproductive disorders. In cattle, sheep and goats, the robertsonian translocation seems to be the most frequent abnormality of chromosome structure. In the pig, reciprocal translocations are very common. The accumulation of data on the frequency of such abnormalities and their effects on reproductive performance prompted an evaluation of their economic consequences in cattle and pigs. In cattle, because of the negative effect of 1/29 translocation, an eradication program, based on the removal of carrier bulls from artificial insemination centers was established. In pig, the main effect of the reciprocal translocations was a reduction in the number of offspring, up to 50%, thus representing a considerable economic loss.

Animals↗

PubMed2006

Reproductive outcomes in recurrent pregnancy loss associated with a parental carrier of a structural chromosome rearrangement.

BACKGROUND: Reproductive outcome studies of couples with a history of recurrent pregnancy loss (RPL) associated with a maternal or paternal carrier of a structural chromosome rearrangement are limited. Correlation of carrier status and cytogenetics of miscarriage specimens is critical to estimate subsequent pregnancy outcome. METHODS: Couples found to have a structural chromosome rearrangement were followed prospectively in a tertiary academic centre. Descriptive analysis and subsequent pregnancy outcomes were tabulated and compared to historic controls. RESULTS: In 1893 RPL couples, 51 carriers of a structural chromosome rearrangement were identified (2.7%). Overall, this cohort had a total of 273 documented pregnancies. Prior to evaluation, the mean maternal age at the time of delivery or miscarriage was 29.8 years and the live birth rate was 15%. Following evaluation and treatment of concomitant factors, there were 58 monitored pregnancies, with a live birth rate of 71%. Amniocentesis was performed on 22% of the ongoing pregnancies; all were diploid or balanced structural chromosome rearrangements. Thirty-six per cent of the miscarriages were found to have an unbalanced structural chromosome rearrangement. CONCLUSIONS: Following evaluation and management of RPL, the live birth rate for carriers of a structural chromosome rearrangement is highly encouraging at 71%, without the addition of assisted reproductive technology.

Abortion, Habitual↗

PubMed1991

Meiotic chromosome structure. Kinetochores and chromatid cores in standard and B chromosomes of Arcyptera fusca (Orthoptera) revealed by silver staining.

The behaviour of two chromosome structures in silver-stained chromosomes was analyzed through the first meiotic division in spermatocytes of the acridoid species Arcyptera fusca. Results showed that at diakinesis kinetochores and chromatid cores are individualized while they associate in bivalents of metaphase I; only kinetochores and distal core spots associate in the sex chromosome. Metaphase I is characterized by morphological and localization changes of both kinetochores and cores which define the onset of anaphase I. These changes analyzed in both autosomes and in the sex chromosome allow us to distinguish among three different substages in metaphase I spermatocytes. B chromosomes may be present as univalents, bivalents, or trivalents. Metaphase I B univalents are characterized by separated cores except at their distal ends and individualized and flat sister kinetochores. At anaphase I sister kinetochores of lagging B chromatids remain connected through a silver-stained strand. The behaviour of cores and kinetochores of B bivalents is identical with that found in the autosomal bivalents. The differences in the morphology of kinetochores of every chromosome shown by B trivalents at metaphase I may be related to the balanced forces acting on the multivalent. The results show dramatic changes in chromosome organization of bivalents during metaphase I. These changes suggest that chromatid cores are not involved in the maintenance of bivalents. Moreover, the changes in morphology of kinetochores are independent of the stage of meiosis but correlate with the kind of division (amphitelic-syntelic) that chromosomes undergo.

Animals↗

PubMed1996

Structural chromosome anomalies in congenital diaphragmatic hernia.

In order to determine the outcome and associated chromosomal and structural anomalies in fetuses diagnosed in utero as having a congenital diaphragmatic hernia, we reviewed 48 consecutive cases referred to our regional Fetal Diagnostic Unit between 1988 and 1995. All babies were delivered in units with appropriate neonatal resuscitation facilities. Thirteen babies [34 per cent of those tested, confidence interval (CI) 19-49 per cent] had karyotypic abnormalities. Three had trisomies but the other nine had more complex karyotypic abnormalities including translocations, deletions, and marker chromosomes. Twenty-one fetuses (44 per cent, CI 30-58 per cent) had additional ultrasound abnormalities which affected the heart in ten cases (21 per cent). Overall, 13 babies survived (27 per cent, CI 14-40 per cent). In babies with normal chromosomes and no additional structural abnormalities the survival rate was 50 per cent (CI 25-75 per cent). Poor outcome was not predicted by early gestation at diagnosis, the hernial contents, or the presence of polyhydramnios. We conclude that parents should be counselled about prognosis with information derived from series of prenatally diagnosed diaphragmatic hernias. The investigations offered should include a detailed ultrasound examination, particularly of the heart, and karyotyping by fetal blood sampling.

Adolescent↗

PubMed2003

Instability of chromosome structure in cancer cells increases exponentially with degrees of aneuploidy.

Structurally altered or marker chromosomes are the cytogenetic hallmarks of cancer cells, but their origins are still debated. Here we propose that aneuploidy, which is ubiquitous in cancer and inevitably unbalances thousands of synergistic genes, destabilizes the structure of chromosomes by catalyzing DNA breaks. Aneuploidy catalyzes such breaks by unbalancing teams of enzymes, which synthesize and maintain DNA and nucleotide pools, and even unbalancing histones via the corresponding genes. DNA breaks then initiate deletions, amplifications, and intra- and interchromosomal rearrangements. Our hypothesis predicts that the rate at which chromosomes are altered is proportional to the degree of aneuploidy: the more abnormal the number and balance of chromosomes, the higher the rate of structural alterations. To test this prediction, we have determined the rates at which clonal cultures of diploid and aneuploid Chinese hamster cells generate new, and thus nonclonal, structurally altered chromosomes per mitosis. Based on about 20 metaphases, the number of new, structurally altered chromosomes was 0 per diploid, 0-0.23 per near-diploid, 0.2-1.4 per hypotriploid, 3.25-4.8 per hypertriploid, and 0.4 per near-tetraploid cell. Thus, instability of chromosome structure increases exponentially with the deviation of ploidy from the normal diploid and tetraploid balances. The particular chromosomes engaged in aneuploidy also affected the rates of chromosome alteration, particularly at low aneuploidy indices. We conclude that aneuploidy is sufficient to cause structural instability of chromosomes. Further, we suggest that certain structurally altered chromosomes encode cancer-specific phenotypes that cannot be generated by unbalancing intact chromosomes. We also extend the evidence for aneuploidy causing numerical instability of chromosomes autocatalytically, and adduce evidence that aneuploidy can cause the many gene mutations of cancer cells that have been attributed to various mutator genes.

Aneuploidy↗

PubMed1981

Alpha-Globin-gene switching during the development of chicken embryos: expression and chromosome structure.

We have analyzed the chromosome structure and expression of the alpha-gene cluster in developing chicken embryos. Using recombinant lambda clones (Dodgson and Engel, 1980), we show a striking relationship between chromosomal regions that are unmethylated, regions that are DNAase I-sensitive and regions that are transcribed. Adjacent regions at both the 5' and 3' sides of the active alpha genes are methylated and relatively insensitive to DNAase I. The active alpha subdomain defined by these assays begins right at the 5' side of the first alpha gene (alpha D) in the active cluster in definitive red cells and extends through a 1.5 kb spacer, into the second alpha gene (alpha A), and 1.5 kb beyond the 3' side of that gene. The sharp boundaries of this subdomain suggest that specific DNA sequences may establish its borders. The extension of the active chromosomal domain beyond the most stable nuclear transcript suggests that transcription may proceed beyond the 3' ends of both alpha A and alpha D. This has been verified by in vitro runoff nuclear transcription. Presumably, poly(A) addition occurs before transcription is terminated. During the switch from the primitive to definitive lineage of erythroblasts, the so-called U gene becomes inactive. This inactivity is reflected in its assembly into a more DNAase-resistant structure. The associated DNA also becomes methylated, and no transcription is detectable by endogenous RNA polymerases. A DNAase I-hypersensitive region at the gene becomes inactivated after the switch to the definitive lineage.

Animals↗

PubMed2003

A unique clone involving multiple structural chromosome rearrangements in a myelodysplastic syndrome case.

In a young female patient presenting with a myelodysplastic syndrome (MDS), a unique clone involving six structural chromosome rearrangements was identified using G-banding and molecular cytogenetic techniques. Fifty GTG-banded metaphases from bone marrow were initially analyzed and all metaphases contained all of the six structural chromosome rearrangements. To further define the GTG-banded karyotype, a series of fluorescence in situ hybridization and primed in situ labeling experiments were performed and the karyotype was then characterized as: 46,XX,r(5)(p13q13),der(20)t(5;20),dup(11)(p11.2p15), r(11)(p15q25),del(13)(q14),idic(22)(p11). The patient quickly progressed to acute nonlymphocytic leukemia three months after the diagnosis and died of a hemorrhage in the brain parenchyma two months later. In this case, the multiple structural chromosome rearrangements conferred an obvious cellular proliferative advantage and indicated a very poor prognosis. Considering that multiple chromosome abnormalities associated with MDS transformation are often polyclonal, this unique clone involving six structural chromosome rearrangements make our case highly unusual.

Adult↗

PubMed1979

Variability between and within laboratories in the analysis of structural chromosomal abnormalities.

The frequency of structural chromosomal aberrations in two samples (AM and PM of the same day) from each of nine normal subjects, cultured in two different laboratories, was studied by six observers. The results were analyzed in order to determine the relative importance of inter- and intralaboratory factors in the variability of chromosomal abnormalities. In addition to the difference in the frequency of the abnormalities between the subjects studied, there were differences due to observers from different laboratories (P less than 0.01), as well as between laboratories (P less than 0.01). These results could be explained in part by insufficient agreement between observers from different laboratories and by differences in the quality of the method used.

Adult↗