RESUMO
In this study, a novel DNA fluorescence labelling technique, called triple helical COMBO-FISH (Combinatorial Oligo Fluorescence In Situ Hybridisation), was compared to the standard FISH (Fluorescence In Situ Hybridisation by means of commercially available probe kits) by quantitative evaluation of the nuclear position of the hybridisation signals of the Abelson murine leukaemia (abl) region and the breakpoint cluster region (bcr) in 3D-conserved cell nuclei of lymphocytes and CML blood cells. Two sets of 31 homopyrimidine oligonucleotides each, corresponding to co-localising sequences in the abl region of chromosome 9 and in the bcr region of chromosome 22 were synthesised. Probe types and sizes (in bases) as well as the binding mechanisms of both FISH techniques were completely different. In accordance to established findings that cell type specific radial positioning of chromosomes and sub-chromosomal elements is evolutionarily conserved, no significant difference was found between the two FISH techniques for the radial localisation of the barycentre of the analysed genomic loci. Thermal denaturation and hypotonic treatment of cell nuclei subjected to standard FISH, however, led to different absolute radii and volumes of the cell nuclei, in comparison to the quantities determined for the triple helical COMBO-FISH technique; the chromatin appears to shrink in laterally enlarged, flat nuclei. Consequently, the absolute distances of the homologous labelled sites shifted to greater values. For precise quantitative microscopic analysis of genomic loci, fluorescence labelling procedures are recommended that well maintain the native chromatin topology. Triple helical COMBO-FISH may offer such an approach.
Assuntos
Genes abl , Hibridização in Situ Fluorescente/métodos , Proteínas Proto-Oncogênicas c-bcr/genética , Sequência de Bases , Estudos de Casos e Controles , Núcleo Celular/genética , Cromossomos Artificiais Bacterianos/genética , Cromossomos Humanos Par 22/genética , Cromossomos Humanos Par 9/genética , Sondas de DNA/genética , Humanos , Leucemia Mielogênica Crônica BCR-ABL Positiva/genética , Linfócitos/ultraestruturaRESUMO
Structural analysis and nanosizing of gene domains requires not only high-resolution microscopy but also improved techniques of fluorescence labelling strongly focussed on the gene domains. To investigate the architecture of abl and bcr in blood cell nuclei forming the Philadelphia chromosome in CML, we applied COMBO-FISH using specifically colocalising combinations of triple strand forming oligonucleotide probes for abl on chromosome 9 and bcr on chromosome 22. Each probe set consisting of 31 homopyrimidine oligonucleotides was computer selected from the human genome database. Measurements by 3D microscopy were compared to results obtained after standard FISH using commercially available abl/bcr BAC probes. The relative radial fluorescence distributions in lymphocyte cell nuclei of healthy donors in comparison to cell nuclei of blood cells of CML patients showed a strong correlation in the location of abl and bcr for both labelling techniques. The absolute distances of the homologous bcr domains and the abl domain-nuclear center-abl domain angles in cell nuclei of CML donors differed significantly from those of healthy donors only when COMBO-FISH was applied. These results indicate that COMBO-FISH may be more sensitive than standard FISH in case of slight modifications in the genome architecture.
