Origin Of Chromosome Abnormalities Research Articles

Cascade of chromosomal rearrangements caused by a heterogeneous T-DNA integration supports the double-stranded break repair model for T-DNA integration.

Transferred DNA (T-DNA) from Agrobacterium tumefaciens can be integrated into the plant genome. The double-stranded break repair (DSBR) pathway is a major model for T-DNA integration. From this model, we expect that two ends of a T-DNA molecule would invade into a single DNA double-stranded break (DSB) or independent DSBs in the plant genome. We call the later phenomenon a heterogeneous T-DNA integration, which has never been observed. In this work, we demonstrated it in an Arabidopsis T-DNA insertion mutant seb19. To resolve the chromosomal structural changes caused by T-DNA integration at both the nucleotide and chromosome levels, we performed inverse PCR, genome resequencing, fluorescence insitu hybridization and linkage analysis. We found, in seb19, a single T-DNA connected two different chromosomal loci and caused complex chromosomal rearrangements. The specific break-junction pattern in seb19 is consistent with the result of heterogeneous T-DNA integration but not of recombination between two T-DNA insertions. We demonstrated that, in seb19, heterogeneous T-DNA integration evoked a cascade of incorrect repair of seven DSBs on chromosomes 4 and 5, and then produced translocation, inversion, duplication and deletion. Heterogeneous T-DNA integration supports the DSBR model and suggests that two ends of a T-DNA molecule could be integrated into the plant genome independently. Our results also show a new origin of chromosomal abnormalities.

A high incidence of chromosome abnormalities in two-cell stage porcine IVP embryos.

In pigs, in vitro production is difficult with a high occurrence of polyspermy and low blastocyst formation rates. To test the hypothesis that this may, at least in part, be due to chromosomal errors, we employed whole genome amplification and comparative genomic hybridization, performing comprehensive chromosome analysis to assess both cells of the two-cell stage in vitro porcine embryos. We thus described the incidence, nature and origin of chromosome abnormalities, i.e. whether they derived from incorrect meiotic division during gametogenesis or aberrant mitotic division in the zygote. We observed that 19 out of 51 (37%) of two-cell stage early pig IVP embryos had a chromosome abnormality, mostly originating from an abnormal division in the zygote. Moreover, we frequently encountered multiple aneuploidies and segmental chromosome aberrations. These results indicate that the pig may be particularly sensitive to in vitro production, which may, in turn, be due to incorrect chromosome segregations during meiosis and early cleavage divisions. We thus accept our hypothesis that chromosome abnormality could explain poor IVP outcomes in pigs.

Human molecular cytogenetics: From cells to nucleotides.

The field of cytogenetics has focused on studying the number, structure, function and origin of chromosomal abnormalities and the evolution of chromosomes. The development of fluorescent molecules that either directly or via an intermediate molecule bind to DNA has led to the development of fluorescent in situ hybridization (FISH), a technology linking cytogenetics to molecular genetics. This technique has a wide range of applications that increased the dimension of chromosome analysis. The field of cytogenetics is particularly important for medical diagnostics and research as well as for gene ordering and mapping. Furthermore, the increased application of molecular biology techniques, such as array-based technologies, has led to improved resolution, extending the recognized range of microdeletion/microduplication syndromes and genomic disorders. In adopting these newly expanded methods, cytogeneticists have used a range of technologies to study the association between visible chromosome rearrangements and defects at the single nucleotide level. Overall, molecular cytogenetic techniques offer a remarkable number of potential applications, ranging from physical mapping to clinical and evolutionary studies, making a powerful and informative complement to other molecular and genomic approaches. This manuscript does not present a detailed history of the development of molecular cytogenetics; however, references to historical reviews and experiments have been provided whenever possible. Herein, the basic principles of molecular cytogenetics, the technologies used to identify chromosomal rearrangements and copy number changes, and the applications for cytogenetics in biomedical diagnosis and research are presented and discussed.

Influence of thyroid hormones on satellite association in man and the origin of chromosome abnormalities.

The satellite association pattern was studied in cells from six hyperthyroid patients before and after antithyroid treatment. The same phenomenon was studied in cells from four healthy control individuals, without any history of thyroid dysfunction. The control cells were cultured in the following media: 1. medium with foetal calf serum and 2–3. media with serum from each of two patients with hyperthyroidism. All analyses were blind studies and were based on 1200 cells (50 cells in each individual sample). Chromosomes No. 21 and 14 (the latter to a lower extent) had a significantly higher association tendency, when the patients were hyperthyroid. The increase in association tendency of No. 21 and 14 was also found when cells from the control individuals were cultured in medium with serum from hyperthyroid patients. Also, chromosome No. 21 and 14 formed association pairs with each other more frequently when the cells were cultured in medium with excess of the thyroid hormones: thyroxin and triiodothyronin. It was concluded that these hormones increase the tendency to satellite association of chromosomes 21 and 14, and may therefore also increase the risk of nondisjunction and of translocation between these chromosomes.

Cytogénétique des ovocytes humains : 40 ans de progrès

Chromosomal abnormalities account for the majority of pre- and post- implantation embryo wastage in humans. Most of these abnormalities result from maternal meiotic errors, which preferentially occur during the first meiotic division. Consequently, the cytogenetic analysis of human oocytes has then been considered as a highly valuable source of data for the investigation of both the occurrence and the origin of chromosomal abnormalities in human. During the last 4 decades, the cytogenetic analysis of human oocytes has never stopped progressing, according to the advents of new technologies. Both karyotyping and molecular cytogenetic studies have been reported to date, providing a large body of data on the incidence and the distribution of chromosomal abnormalities in human female gametes. However, these studies display a great variability in results, which may be essentially attributable to the limitations of these techniques when applied to human oocytes. The most relevant analysis have led to the estimate that 15-20% of human oocytes present chromosome abnormalities, and they have emphasized the implication of both whole chromosome non-disjunction and chromatid separation in the occurrence of aneuploidy in human oocytes. The effect of advanced maternal age on the incidence of aneuploidy in human oocytes has also been clearly evidenced by recent reports based on large sample of oocytes or polar bodies.

The cytogenetics of preimplantation human development: insights provided by traditional and novel techniques

Our understanding of the incidence and origin of chromosome abnormalities in human preimplantation embryos is very limited due to the necessary ethical constraints involved in studying such material and the limited data ultimately produced. Several studies have addressed this issue, however, using techniques such as interphase fluorescence in situ hybridisation, modified G-banding preparation and the use of single-cell comparative genomic hybridisation (CGH). This review discusses the use of these techniques in assessing chromosome abnormalities in this, the earliest of human developmental stages. In addition, the prospects for the clinical use of CGH are discussed.

Cytogenetic analysis of human zygotes displaying three pronuclei and one polar body after intracytoplasmic sperm injection.

Digynic zygotes with three pronuclei and one polar body obtained after intracytoplasmic sperm injection (ICSI) were studied cytogenetically to elucidate the frequency and origin of chromosomal abnormalities at the earliest stage of conception. Uncleaved, single-cell zygotes were incubated with podophyllotoxin and vinblastine and fixed by a gradual fixation air drying method. The chromosomes were stained with Giemsa. Twenty-two (50%) out of 44 informative zygotes revealed cytogenetic alterations, including aneuploidy (six cells, 13.6%), structural aberrations (10 cells, 22.7%) and combinations of numerical and structural abnormalities (two cells, 4.5%). In one case (2.3%), double aneuploidy or an effect of chromosomal translocation could not be distinguished and one zygote (2.3%) turned out tetraploid due to injection of a diploid spermatozoon. Two zygotes (4.5%) showed an irregular chromatid segregation between the two maternal complements. In completely analysable cells, the sex chromosome ratio XXX:XXY was 17:15. Digynic ICSI zygotes carry a high rate of cytogenetic abnormalities that obviously have been transmitted by the participating oocytes and spermatozoa. We also confirmed the previously reported, possibly ICSI-induced irregular oocyte chromatid segregation. The results suggest that aneuploidy in the oocytes must have been caused by predivision instead of non-disjunction.

Origin of Chromosomal Abnormalities: Evidence for Delayed Fertilization in Meiotic Nondisjunction

Department of Medical Genetics, Children's Medical Center, Dayton; and Department of Pediatrics, Wright State University, Dayton, Ohio

Origin of chromosomal abnormalities in nuclear transplants—A reevaluation of nuclear differentiation and nuclear equivalence in amphibians

Previous transplantation tests of amphibian nuclei derived from advanced somatic and germinal cell types have demonstrated that most of these nuclei have acquired developmental restrictions during embryogenesis. The nature of these restrictions has been revealed in part through chromosomal studies of abnormal nuclear transplants. In these studies, it has been found that the developmental restrictions in the nuclear transplants are accompanied in most cases by karyotypic alterations. In order to determine the origin of these chromosomal aberrations and thereby gain some understanding of the chromosomal changes accompanying normal embryogenesis, we have studied the nuclear and chromosomal morphology of nuclear transplants within the first 8 hours after nuclear transplantation. These studies carried out on nuclei of determined endodermal cells demonstrate that in most cases the origin of these chromosomal aberrations is traceable to the initial responses of the transplanted nucleus to the cytoplasm of the recipient egg. Many transplanted endodermal nuclei fail to undergo sufficient nuclear enlargement and chromatin decondensation. As a result of these events, chromatid bridges arise during the first mitotic cleavage and subsequent to chromatid breakage at late anaphase, variable deletions in chromosomes occur. These different amounts of genetic losses then lead to variable abnormal development in nuclear transplants and ultimately are the cause of developmental arrest. The results of these studies indicate that during embryogenesis the chromosomes of many endodermal nuclei have acquired restrictions in the form of condensed or compact chromatin (heterochromatin). Furthermore, these restrictions are not reversed completely by transplantation into young egg cytoplasm; and consequently, the complete expression of the transplanted nucleus is prevented. The significance of these findings is discussed in relation to our current understanding of nuclear differentiation in amphibians.