Insights into the structure of the subtelomeric chromosome segments

Drets, Máximo E.

doi:10.1590/s1415-47572000000400056

Cited by 4 publications

(3 citation statements)

References 45 publications

(38 reference statements)

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“…Summarizing, even though the information presently available on the molecular analysis of the telomeric/subtelomeric DNA and associated protein complexes is considerable, a clear picture of the eukaryotic metaphase chromosome at the high level organization is still missing (Drets, 2000). The metaphase subtelomeric segments proved not to be a simple association of DNA and protein molecules linearly aligned but an intricate and compact structure with functional roles not completely understood and awaiting definition.…”

Section: Cytogenetic and Molecular Perspectivesmentioning

confidence: 99%

Cytological indications of the complex subtelomeric structure

2004

Cytogenet Genome Res

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Research on the subtelomeric region has considerably increased because this chromosome segment (1) keeps the chromosome number constant, (2) intervenes in cancer and cell senescence processes, (3) presents more crossovers than other regions of the genome and, (4) is the site of cryptic chromosome aberrations associated with mental retardation and congenital malformations. Quantitative microphotometrical scanning and computer graphic image analysis enables the detection of differentially distributed Giemsa-stained structures in T-banded subtelomeric segments of human and Chinese hamster ovary (CHO) chromosomes. The presence of high density stain patterns in the subtelomeric region was confirmed using endoreduplicated chromosomes as a model. Besides, prolonging the incubation in the T-buffer, specific holes were induced in subtelomeric segments. Hole specificity was confirmed inducing them in complex CHO chromosome aberrations obtained by AluI. The method was also used to detect minute sister chromatid exchanges in the T-banded subtelomeric area (t-SCEs). The presence of t-SCEs was suspected to reflect, at the microscope level, the high crossover activity prevailing in the region. Due to the fact that the fluorescent signals obtained with subtelomeric probes seem to be colocalized with subtelomeric high density areas, measurements on the position of both structures with respect to the diffraction and chromosome edges were carried out. Data obtained showed comparable values suggesting that the high density segments were located where telomeric probes usually fluoresce. The possible relationship of the high density patterns, the production of specific holes, the localization of fluorescent areas and the detection of minute SCEs in the subtelomeric segment observed in T-banded CHO and human chromosomes is briefly reviewed.

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Section: Cytogenetic and Molecular Perspectivesmentioning

confidence: 99%

Cytological indications of the complex subtelomeric structure

2004

Cytogenet Genome Res

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“…The detection of similar patterns in endoreduplicated T-banded CHO chromosomes through microdensitometric scanning and computer graphic image analysis indicated that the differential distribution of HD chromatin was not due to a methodological artifact since it replicated in the same manner in the terminal region of both sister chromosomes (Drets, 2000). Moreover, T-banded segments of human and CHO chromosomes sometimes exhibited HD chromatin areas distributed like minute sister chromatid exchanges (Drets et al, 1992), what we recently called ter-SCE (Drets et al, 2006).…”

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Non-random distribution of high density chromatin detected at opposite ends of T-banded human metaphase chromosomes

Santiñaque

Drets

2007

Genet. Mol. Biol.

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Previous research using microdensitometric scanning and computer graphic image analysis showed that T-banded segments of human metaphase chromosomes usually exhibit an asymmetrical distribution of high density (HD) chromatin between sister chromatids. Here, we employed the same methods to analyze HD chromatin distribution at opposite ends of T-banded human lymphocyte chromosomes. This study revealed that in most chromosomes with an asymmetrical distribution of HD chromatin at both ends, the highest densities of each arm were located in opposite chromatids. The frequency of this configuration was 0.792 per chromosome, indicating that the highest chromatin densities of the terminal segments of T-banded human chromosomes were non-randomly distributed at opposite chromosome arms. The possible relationship of this observation to the mode of replication of the terminal chromosome region is briefly discussed.Key words: human chromosomes, T-banding, chromatin structure, telomere, microdensitometry. It is well known that the usual banding procedures (C-, G-, R-and T-) reveal the underlying structure and composition of DNA and associated proteins in mitotic chromosomes (Therman and Susman, 1993). The specialized chromatin structure and the GC-richness of the telomeric/ subtelomeric DNA (de Lange, 2005;Riethman et al., 2004) confer high resistance to heat denaturation to the terminal regions of metaphase chromosomes which results in selective staining after T-banding (Dutrillaux, 1973). T-banding is a modification of R-banding procedure and is obtained through the incubation of chromosomes in a buffer at a high temperature followed by Giemsa staining. This procedure results in T-bands as darkly stained segments in lightly stained chromosomes. Scanning electron microscopy showed that T-bands are areas of highly aggregated chromatin fibres (Jack et al., 1986;Allen et al., 1988).Microdensitometric scanning and computer graphic image analysis of high-resolution microphotographs of Tbanded segments of human and Chinese Hamster Ovary (CHO) chromosomes allowed the detection of a differential distribution of HD sub-telomeric chromatin between sister chromatids. The different patterns observed were arbitrarily classified in three kinds of HD chromatin distribution, namely: Type I, HD segments were of similar size in both sister chromatids; Type II, HD predominated in one of the chromatids; and Type III, HD was detected in only one chromatid (Drets et al., 1992). Alternatively, the distribution of HD chromatin could be classified in a simplified way as symmetrical (pattern type I) or asymmetrical (patterns type II and III). These patterns were confirmed by scanning T-banded endoreduplicated CHO chromosomes in which the same interchromatid distribution of HD chromatin appeared in both sister chromosomes (Drets and Mendizábal, 1998). Nevertheless, quantitative computerized microdensitometrical analyses on the distribution of HD chromatin at opposite ends of T-banded chromosomes have not yet been reported. Therefore, we perform...

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“…Particularly, human chromosomes termini display elevated rates of mitotic recombination (Cornforth and Eberle, 2001). ter SCE as well as subtelomeric cryptic aberrations associated with severe clinical conditions could reflect a high functional activity of this chromosome region (Obe et al, 2002;Drets 2000 and2004).…”

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A proposal of a standardised nomenclature for terminal minute sister chromatid exchanges

Drets¹,

Santiñaque²,

Obe³

2006

Genet. Mol. Biol.

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We described spontaneous minute sister chromatid exchanges (SCE) in telomeric regions of human and Chinese hamster ovary (CHO) chromosomes more than 10 years ago. These structures, which we called t-SCE, were detected by means of highly precise quantitative microphotometrical scanning and computer graphic image analysis. Recently, several authors using the CO-FISH method also found small SCEs in telomeric regions and called them T-SCE. The use of different terms for designating the same phenomenon should be avoided. We propose ter SCE as a uniform nomenclature for minute telomeric SCEs.

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Insights into the structure of the subtelomeric chromosome segments

Cited by 4 publications

References 45 publications

Cytological indications of the complex subtelomeric structure

Cytological indications of the complex subtelomeric structure

Non-random distribution of high density chromatin detected at opposite ends of T-banded human metaphase chromosomes

A proposal of a standardised nomenclature for terminal minute sister chromatid exchanges

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