Somatic S-phase pairing of homologous chromosome 3 in interphase nuclei of human peripheral blood lymphocytes

Distances of homologous centromeres and telomeres of human chromosomes were interactively measure din relation to the nuclear diameter. In total about 2000 cell nuclei were acquired by fluorescence microscopy. Here the results are presented for two color fluorescence in situ hybridization (FISH) applied to lymphocyte cell nuclei using commercially available DNA probes for chromosome 3 centromere and 3p- telomere. In 89 cell nuclei (66%) of the homologous centromeres had a distance Dc smaller than 15 percent of the nuclear diameter (dn). For these per definition classified 'paired' centromeres an increased frequency of small distances of homologous telomeres (Dt) was found. Stimulated S-phase cell nuclei were identified by incorporation of bromodeoxyuridine and simultaneous fluorescence labeling by anti-BrdU antibodies. In this case only the centromeres were FISH labeled. Of 301 cell nuclei about 187 (62%) were stimulated and among them 77 (41%) were paired according to the above mentioned criterion (Dc<0,15 dn). These results indicate that proliferating blood lymphocytes show a considerable tendency to centromere pairing. Assuming that the chromosome arm is probably localized between centromere and telomere with a homologous chromatin density, it may be concluded from the data that somatic pairing of whole chromosomes occurs preferentially during S-phase of the cell nucleus.