Cytological indications of the complex subtelomeric structure.

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.

Chromosomal aberrations: formation, identification and distribution.

Chromosomal aberrations (CA) are the microscopically visible part of a wide spectrum of DNA changes generated by different repair mechanisms of DNA double strand breaks (DSB). The method of fluorescence in situ hybridisation (FISH) has uncovered unexpected complexities of CA and this will lead to changes in our thinking about the origin of CA. The inter- and intrachromosomal distribution of breakpoints is generally not random.

The underlying structure of the subtelomeric region detected by microphotometrical scanning and chromosome graphic image analysis.

Previous research showed that the microphotometrical scanning of T-banded subtelomeric regions reveals the presence of specific patterns of the Giemsa stain density distributions as detected in chromosomes of normal human lymphocytes and CHO cells. Analyses with this method of the T-banded subtelomeric segments of CHO endoreduplicated chromosomes confirmed that these density patterns replicate in a similar way in sister chromosomes. Besides, the specific removal of portions of the subtelomeric segments appearing as tiny holes located where these density patterns are found suggested that both phenomena are related.

Computer graphics as a tool in cytogenetic research and education.

Scanning microscope photometry has been extensively used for image analysis of nuclei and chromosomes and for automated karyotyping. Color graphics terminals, software development and appropriate data manipulation have expanded the scope of scanning microphotometry so that it is now particularly useful for the quantitative analysis of cell components. We have developed application software for displaying nuclear and chromosome densities on a computer terminal of in the form of pixeled images and pseudo-three-dimensional graphic diagrams, as well as for image transformation, object illumination and rotation to enhance chromatin features.

Clastogenic action of a dimethyl p-benzoquinone of animal origin.

The cytogenetic action of a volatile dimethyl p-benzoquinone found in the natural secretion of an arachnid (Acanthopachylus aculeatus Kirby) was studied in cultured human peripheral leukocytes and in mouse bone-marrow cells. Continuous and pulse treatments carried out in vitro, as well as experiments performed in vivo, induced different chromatid and chromosome aberrations suggesting that this chemical has clastogenic properties. The biology of the animal and the possible role of one of the components of its secretion as a natural mutagenic agent are discussed.

Chromosome delineation induced by a combined potassium permanganate-sodium bisulfite treatment.

A cytological procedure for in vitro chromosome delineation has been studied using human and mouse (Mus musculus) chromosomes. This method, consisting of slide incubation in KMnO4 at 0--5 degrees C for 24 h followed by a short exposure to NaHSO3 (1--3 min) and Giemsa staining, induces extraction of chromatin from human and mouse interphase nuclei and chromosomes. Autoradiography after 3H-ThD incorporation in vitro and cytophotometry confirmed that DNA is removed.

BANDSCAN--a computer program for on-line linear scanning of human banded chromosomes.

BANDSCAN, an interactive program for on-line linear scanning of human G-banded chromosomes quantitative analysis is described. This program was written for a Wang 720 C programmable desk calculator associated to the Zeiss scanning photometer MP01. The system can detect up to a maximum of 24 densitometric band peaks found along banded chromosome arms or chromatids, estimate the total arm length and localize bands in terms of their relative positions.

Aanlysis of the frequency and distribution of sister chromatid exchanges in cultured human lymphocytes.

Lymphocytes from 20 notmal subjects (11 male and 9 female) were examined for the frequency and location of sister chromatid exchanges (SCE) by the BrdU--Giemsa method. The mean frequency of SCE was 6.37 with little significant variation.

Mechanisms of chromosome banding. IX. Are variations in DNA base composition adequate to account for quinacrine, Hoechst 33258 and daunomycin banding?

Prior studies on subfractions of mouse and Kangaroo rat DNA have suggested that variations in base concentration within a given genome may not be great enough to account for Q-banding. To examine this with another species, calf DNA was subfractionated by CsCl ultracentrifugation into GC-rich satellites and the main band DNA was further fractionated into AT-rich, intermediate and GC-rich portions. The effect of varying concentrations of these DNAs on quinacrine and Hoechst 33258 fluorescence was examined.

Specific banding patterns of human chromosomes.

Individual pairs of human chromosomes can be reliably identified by a new method that does not require special optical equipment and that results in permanent preparations. This method, which is based on treatment of the chromosomes in situ with NaOH, followed by incubation in sodium chloride-trisodium citrate and Giemsa staining, results in highly specific banding patterns in characteristic regions of the chromosome arms. It should prove useful for the detection of small structural changes in chromosomes.