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PubMed1983

Eukaryotic genome: model considerations.

The paper presents a new model of chromosome structure based on the assumption that multiple circular subunits of DNA exist. The essential difference with previously described models is the circular DNA unit forms a central chromosome axis. Chromosome configurations during various phases of the cell cycle depend on the various conformations of this central integrating unit. The described model can be generalized for all haploid set of eukaryotic nucleus. Some aspects of the chromosome structure and their functions have been discussed.

Animals↗
PubMed1995

Culture of pachytene spermatocytes for analysis of meiosis.

An impediment to the investigation of mammalian spermatogenic meiosis has been the lack of an appropriate system for experimental manipulation of meiotic prophase cells. We report here the use of a simple system for the short-term culture of pachytene spermatocytes. We have assayed parameters of cell function pertinent to meiotic prophase, namely chromosome pairing and synapsis. During the culture period of 24-48 hr, cells maintained typical pachytene morphology, chromatin condensation patterns, and chromosome pairing, as assessed by light and electron microscopy. Uridine incorporation, monitored by autoradiography, reflected the chromosomal distribution found in vivo in that the autosomal chromosomes were transcriptionally active, while the sex chromosomes were not. Thus features of chromosome pairing and sex chromatin inactivation are maintained in these cultures. We have conducted experiments to demonstrate that cultured pachytene spermatocytes can be useful for the analysis of agents, some of which may be suspected mutagens, that might affect chromosome structure and function during meiosis. Treatment of cells with actinomycin D revealed a differential effect on chromatin condensation in the autosomes versus the sex chromosomes. Camptothecin, a topoisomerase inhibitor, induced desynapsis of paired chromosomes. Okadaic acid, a phosphatase inhibitor, induced premature metaphase-I condensation of pachytene chromosomes. This last experiment suggests that these cultured cells may be useful for analysis of meiotic cell cycle controls. Taken together, these results demonstrate a culture system that can be useful for analysis of meiotic events as well as in screening for potential mutagenic agents that might affect meiotic chromosome structure and function.

Animals↗
PubMed2002

Scanning probe microscopy for chromosomal research.

The study of chromosome structure with scanning probe microscopy provides a range of information from three-dimensional topographic structures through mechanical properties to optical information, usually fluorescence. For atomic force microscopy studies, the importance of removing cell debris from the chromosome surface has been recognized. Studies in aqueous environments reveal a highy swollen and tough chromosomal structure, but the charge interaction between the probe and specimen needs to be considered if high-resolution images are to be achieved. This charge interaction can be used to extract DNA strands of about 2 kbp from the chromosome. SPM studies of chromosomes may also be of value in the identification of defective chromosomes with either duplications or deletions.

Chromosomes, Human↗
PubMedDate not supplied

Comparison of transforming, antimitotic and chromosomal aberration-inducing properties of melphalan and cyclophosphamide.

Melphalan and cyclophosphamide, cytostatics used for cancer therapy, were investigated for their ability to induce morphological transformation of embryonic cells of the golden hamster and to evoke structural chromosome aberrations. The antimitotic action of both drugs was also investigated. Cyclophosphamide, under conditions in which it did not produce either structural chromosomal aberrations or exerted cytotoxic action, induced morphological transformation of hamster cells. Under the experimental conditions melphalan induced morphological transformation of hamster cells at concentrations not inducing chromosomal aberrations.

Animals↗
PubMed2000

The expression of fragile sites in lymphocytes of patients with rectum cancer and their first-degree relatives.

Fragile sites are non-staining gaps and breaks in specific points of chromosomes. These sites also include acentric fragments, triradial figures and several rearrangements. Although this issue has been controversial recently, they may be related to structural chromosomal rearrangement in some neoplasms. In this study, the expression of fragile sites induced by aphidicolin (Apc), 5-bromodeoxyuridine (BrdU) and caffeine was investigated on prometaphase chromosomes obtained from the peripheral blood lymphocytes of 36 patients with rectum cancer, 30 first-degree relatives and 30 normal healthy controls. The results of the structural chromosome aberrations determined in patients and their first-degree relatives were significantly higher than those in control subjects (P<0.001). We determined aphidicolin type common fragile sites (1p36, 1p31, 1p21, 1q21, 1q25, 1q44, 2p24, 2q21, 2q33, 2q37, 3p14, 5q21, 5q33, 13q13, 14q24, 16q23 and 18q21). When the rates of sites such as 1p21, 1q25, 2q33, 3p14, 5q21 and 14q24 in patients and in their first-degree relatives were compared with the control group, the difference was statistically significant. Our results indicated an increased genetic instability in patients with rectum cancer and their first-degree relatives. Therefore, the increase of fragile site expression may be an important marker showing genetic predisposition to rectum cancer.

Adult↗
PubMed1996

Gene structure and chromosome localization to 7q21.3 of the human rod photoreceptor transducin gamma-subunit gene (GNGT1).

The transducin gamma-subunit gene (GNGT1) encodes a member (gamma1) of the family of heterotrimeric G-protein gamma-subunits that is specific to rod photoreceptors. In this report we have determined the complete structure of the GNGT1 gene and have localized it to human chromosome 7q21.3 using somatic cell hybrid and yeast artificial chromosome analysis.

Amino Acid Sequence↗
PubMed1979

Chromosome changes and benzene exposure. A review.

Benzene exposure can induce chromosome aberrations in somatic cells (lymphocytes and bone marrow cells) of man and of experimental animals in vivo, as well as in some in vitro systems. Numerical and structural chromosome changes in bone marrow cells have been described in subjects with benzene haemopathy. Increased rates of structural chromosomal aberrations both of the "unstable" and of the "stable" type in cultured peripheral blood lymphocytes have been observed not only in subjects with chronic benzene poisoning, but also in individuals with past benzene haemopathy and in subjects with past benzene exposure without signs of poisoning; these findings persisted for years or decades after cessation of exposure. In some cases of benzene-induced leukaemias the cytogenetic pattern was variable, as it is true also for the "spontaneous" acute leukaemias. The possible implications of the finding of chromosome damage from benzene to bone marrow cells for the occurence of leukaemias are discussed. The possibilities and limitations of cytogenetic studies in the biological monitoring of subjects exposed to benzene are commented on.

Adult↗
PubMed2000

Structure and chromosomal localization of the mouse SNAP-23 gene.

SNAP-23 plays an important role in the regulation of vesicle trafficking in mammalian cells. In this report, we have determined the exon/intron organization of the mouse SNAP-23 gene. The SNAP-23 gene spans 31kb of the mouse genome and consists of eight exons interrupted by seven introns. The exon organization of the mouse SNAP-23 gene is identical to that of the related SNAP-25 gene in both chicken and Drosophila, suggesting that SNAP-23 arose by duplication of the SNAP-25 gene. Primer extension analysis revealed a major transcription start site approximately 112bp upstream of the translation start site. Like many ubiquitously expressed housekeeping genes, the proximal promoter region for the mouse SNAP-23 gene lacks consensus TATA and CAAT boxes. The SNAP-23 gene was localized to mouse chromosome 2 at band 2E5 using both fluorescence in-situ hybridization and radiation hybrid panel mapping studies. The identification of the structure of the mouse SNAP-23 gene reveals that the overall exon organization of SNAP-25 family members is conserved throughout evolution.

Amino Acid Sequence↗
PubMed1999

Genomic structure and chromosomal mapping of the human sterol regulatory element binding protein (SREBP) cleavage-activating protein (SCAP) gene.

Sterol regulatory element binding protein (SREBP) cleavage-activating protein (SCAP) is a central regulator of lipid synthesis and uptake in mammalian cells. The entire genomic structure of the human SCAP gene was cloned in a 110-kb region covered by overlapping genomic clones. The SCAP gene was localized to chromosome 3p21.3 by fluorescence in situ hybridization. The human SCAP gene is over 30 kb in length and contains 23 exons and 22 introns. The transcription initiation site within exon 1 is separate from the initiation codon coded in exon 2. Analysis of exon/intron structure revealed that the gene consists of a mosaic of exons encoding functional protein domains. Exon 1 encodes the 5' non-coding region. Exons 2, 3, 7, 8, 9, 10, 11, 13, and 15, respectively, encode each of the eight transmembrane regions. Of these, exons 7-11 encode the sterol-sensing domain. Exons 15-23 encode the hydrophilic carboxyl-terminal domains containing four copies of a motif called the Trp-Asp (WD) repeats that interact with and regulate SREBP and the site-1 protease. Sequence analysis of the 5'-flanking region showed that it comprised a high G/C-rich region and contained adipocyte determination and differentiation-dependent factor 1 (ADD1)/SREBP-1 binding sites in addition to Sp1 and AP2 sites. This suggests that SCAP gene expression is under the control of SREBP-1, a key regulator of the expression of genes essential for intracellular lipid metabolism. Our data establish the basis of investigation for molecular variants in this gene that may result in alterations in plasma lipoprotein levels and/or derangement of intracellular lipid metabolism.

Base Sequence↗
PubMed2000

Structure and chromosome location of Smtn, the mouse smoothelin gene.

Smoothelins are cytoskeleton-associated proteins that are found in contractile smooth muscle. Two isoforms have been identified: smoothelin-A, expressed in visceral tissues and smoothelin-B, found in vascular tissues. The mouse smoothelin gene (Smtn) was isolated and characterized. It was assigned to chromosome 11 band A2-A3 by fluorescence in situ hybridization. The gene consists of 20 exons and spans 23 kb. Its structure is conserved between mouse and human. The proximal promoter of both smoothelin-A and smoothelin-B contains several transcription factor-binding sites but lacks a consensus TATA box.

Animals↗
PubMed1998

No induction of chromosome aberrations in human spermatozoa exposed to extremely low frequency electromagnetic fields.

Clastogenic effects of extremely low frequency electromagnetic fields (ELF-EMFs) on human sperm chromosomes were studied using an interspecific in vitro fertilization system with zona-free golden hamster oocytes. Semen samples from healthy men were exposed to ELF-EMFs (50 Hz, 20 mT) for 2 h at 37 degreesC under 5% CO2 in air. The samples were then cryopreserved in liquid nitrogen for shipment to a cytogenetic laboratory. After thawing the samples, motile spermatozoa were collected using a continuous Percoll density gradient centrifugation and then capacitated for in vitro fertilization with hamster oocytes. Sperm-derived chromosomes were analyzed at first cleavage metaphase. The present experiment was performed twice using semen samples from two different donors. In test-1, incidence of spermatozoa that displayed structural chromosome aberrations was 17.0% (35/206) in the exposed group and 20.8% (55/264) in the control group. In test-2, structural chromosome aberrations were observed in 11.1% (13/117) of exposed spermatozoa and 13.8% (13/94) of spermatozoa in the control group. In both tests, there was no significant difference in the incidence of chromosomally abnormal spermatozoa between the exposed group and the control group. Types of aberrations observed and their incidences per spermatozoon in the exposed group were similar to those of the control group. Despite the small sample size, the present results suggest that ELF-EMFs have no clastogenic effect on human sperm chromosomes.

Animals↗
PubMed2000

Genomic structure and chromosome location of the mouse RelA p65 gene (Rela).

The RelA (p65) subunit of transcription factor NF-kappaB plays a critical role in development, and rela(-/-) knockout mice die in utero from massive liver apoptosis. Only partial sequences of the mouse Rela gene are available. We have determined the genomic structure of mouse Rela and promoter, and have mapped the gene to chromosome 19B1-3.

Animals↗
PubMed1995

Cloning, structure, and chromosome localization of the mouse glutaryl-CoA dehydrogenase gene.

Glutaryl-CoA dehydrogenase (GCDH) is a nuclear-encoded, mitochondrial matrix enzyme. In humans, deficiency of GCDH leads to glutaric acidemia type I, an inherited disorder of amino acid metabolism characterized by a progressive neurodegenerative disease. In this report we describe the cloning and structure of the mouse GCDH (Gcdh) gene and cDNA and its chromosomal localization. The mouse Gcdh cDNA is 1.75 kb long and contains an open reading frame of 438 amino acids. The amino acid sequences of mouse, human, and pig GCDH are highly conserved. The mouse Gcdh gene contains 11 exons and spans 7 kb of genomic DNA. Gcdh was mapped by backcross analysis to mouse chromosome 8 within a region that is homologous to a region of human chromosome 19, where the human gene was previously mapped.

Amino Acid Sequence↗
PubMed2003

Associations between inverted repeats and the structural evolution of bacterial genomes.

The stability of the structure of bacterial genomes is challenged by recombination events. Since major rearrangements (i.e., inversions) are thought to frequently operate by homologous recombination between inverted repeats, we analyzed the presence and distribution of such repeats in bacterial genomes and their relation to the conservation of chromosomal structure. First, we show that there is a strong under-representation of inverted repeats, relative to direct repeats, in most chromosomes, especially among the ones regarded as most stable. Second, we show that the avoidance of repeats is frequently associated with the stability of the genomes. Closely related genomes reported to differ in terms of stability are also found to differ in the number of inverted repeats. Third, when using replication strand bias as a proxy for genome stability, we find a significant negative correlation between this strand bias and the abundance of inverted repeats. Fourth, when measuring the recombining potential of inverted repeats and their eventual impact on different features of the chromosomal structure, we observe a tendency of repeats to be located in the chromosome in such a way that rearrangements produce a smaller strand switch and smaller asymmetries than expected by chance. Finally, we discuss the limitations of our analysis and the influence of factors such as the nature of repeats, e.g., transposases, or the differences in the recombination machinery among bacteria. These results shed light on the challenges imposed on the genome structure by the presence of inverted repeats.

Chromosome Inversion↗
PubMed2004

Chromosome analysis of mouse zygotes after injecting oocytes with spermatozoa treated in vitro with green tea catechin, (-)-epigallocatechin gallate (EGCG).

The cytogenetic effects of (-)-epigallocatechin gallate (EGCG) on mouse spermatozoa were studied in vitro using an intracytoplasmic sperm injection (ICSI) technique. Spermatozoa were collected by the swim-up method and treated with EGCG at 1 microM and 10 microM. When motile, EGCG-treated spermatozoa were injected into oocytes, structural chromosome aberrations (SCAs) at the first cleavage metaphase did not increase significantly. However, a majority of immotile spermatozoa treated with 10 microM EGCG had the following abnormalities: pronuclear arrest (11% of activated oocytes), degenerated sperm chromatin (chromosome) mass (30% of activated oocytes) and occurrence of structural chromosome aberrations (57% of analyzed metaphases). The incidence of these abnormalities suggests that immotile spermatozoa were susceptible to EGCG, and that the damage of sperm chromatin was accelerated in immotile spermatozoa by 10 microM EGCG treatment.

Animals↗
PubMed1999

Genomic structure and chromosomal localization of the mouse persyn gene.

Synucleins are a family of small intracellular proteins expressed mainly in the nervous system. The involvement of synucleins in neurodegeneration and malignancy has been demonstrated, but the physiological functions of these proteins remain elusive. Further studies including generation of animals with modified persyn expression are necessary to clarify the functions of these proteins and the mechanisms of their involvement in human diseases. We cloned and determined the organization and chromosomal localization of the mouse gene coding for persyn, a member of the synuclein family. The gene is composed of five exons, and its general structure is very similar to that of the human persyn gene. Using fluorescence in situ hybridization, we assigned the persyn gene to the boundary of bands B and C on mouse chromosome 14. We found a fragment of the gene that directs expression of the persyn protein in sensory neurons and could be used for generation of transgenic animals.

3T3 Cells↗
PubMed1975

X-ray and UV-induced chromatid aberrations: evidence for polynemic chromosomes?

Ikushima and Wolff have recently interpreted both their observation of chromatid aberrations in second and third mitoses following X-irradiation and the production of chromatid type chromosomal aberrations by UV light administered during the G1 phase of the cell cycle in terms of a polyneme model of eukaryote chromosome structure. They were led to do so, however, largely because of their X-ray data, which the interpreted as evidence for the induction of sub-chromosomal lesions (by G1 irradiation; sub-chromatid for G2 irradiation) which appear as chromatid type aberrations only in later divisions. We here report data from similar X-ray experiments in which synchronized Chinese hamster tissue culture cells were irradiated in either G1 or G2 and then scored for chromatid aberrations in their first, second and third post-irradiation mitoses. Our results do not show the effect reported by Ikushima and Wolff. We conclude that all of the data available of aberration production is compatible with a simple mononeme model of eukaryote chromosome structure.

Animals↗
PubMed2002

Genome restructuring in rye affects the expression, organization and disposition of homologous rDNA loci.

The standard rye cultivar 'Imperial' and a structural variant carrying an intact 1R chromosome and two telocentric 1R chromosomes (short and long arms) were used to investigate expression patterns of homologous rDNA loci, and the influence of chromosome structural change on their interphase organisation and relative disposition. Sequential silver staining and in situ hybridization with the rDNA probe pTa71, established a correspondence between the expression and organization patterns of rDNA domains in metaphase and interphase cells. In most cells of the cultivar Imperial, nucleolar organizer region (NOR) silver staining on metaphase chromosomes with equivalent numbers of rDNA genes revealed a size heteromorphism between homologous rDNA loci, resulting from their differential expression. NOR heteromorphism in the structural variant line was significantly reduced. The preferential activity of one NOR over its homologue was found to be random within cells and independent of parental origin. Nucleotypic modifications mediated by changes in the 1R chromosome structure include increased proximity between homologous rDNA loci in interphase, and an increase in the frequency of cells with intra-nucleolar ribosomal condensed chromatin. These results seem to indicate a 'sequence recognition' process for the regulation of homologous loci.

Cell Cycle↗