Interactive computer-assisted analysis of chromosome 1 colocalization with nucleoli.

The applications of DNA cloning and fluorescent in situ hybridization (FISH) techniques have strengthened the hypothesis of an ordered chromatin structure in interphase nuclei, strongly suspected to vary with functional state. The nonrandom distribution of the centromeres and their dynamic rearrangement during the cell cycle have been well documented. A close proximity of specific centromeres to nucleoli has also been reported, but the functional meaning of this association is still unknown. In order to investigate whether the chromosome 1 centromere region to nucleolus association depends on the cell cycle and chromosome status, we combined FISH of probes specific for the 1q12 region with Ki-67 nucleolar antigen fluorescent immunocytochemical (FICC) detection on the MCF-7 human breast cancer cell line and on the MRC-5 normal fibroblastic cell line. Both FISH and FICC signals were interactively localized in a one-step fluorescent microscopic observation and further analyzed using the Highly Optimized Microscope Environment (HOME) graphics microscope workstation, which provided computerized interactive marking of 1q12 to nucleolus associations (1q12-nu) at the individual nucleus and nucleolus levels. This study confirms that centromeric regions, other than those adjacent to the major ribosomal cistrons, contribute to the perinucleolar chromatin and demonstrate that, during the cell cycle, the heterochromatic band 1q12 is dynamically rearranged with regard to both the nuclear volume and the nucleoli. A relationship between the association of the chromosome 1 pericentromeric region with nucleoli and the nucleolar transcriptional activity is also strongly suggested.