Cytological indications of the complex subtelomeric structure

Abstract

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.

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

“…This may indicate that the highly heat-resistant HD areas could interfere with DNA accessibility to telomere probes. In human metaphase chromosomes, HD chromatin T-banded areas co-localize with fluorescent signals of FITC-labeled telomere PNA probes (CCCTAA), which are non-strictly localized at the end of the chromatids (Drets, 2004;Moyzis et al, 1988;Steinmüller et al, 1993). Interestingly, the TRANS and CIS configurations frequencies found here are comparable to those obtained in normal human mitotic chromosomes using telomeric CO-FISH, a method that allows to differentiate between telomeres that replicated through lagging-or leading-strand synthesis (Cornforth and Eberle, 2001).…”

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

“…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).…”