Genomic architecture and evolutionary organization by three-dimensional nuclear positioning of chromosome territories in mammalian species especially in primates

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Chromosome territories (CTs) in mammalian cell nuclei are highly compartmentalized as distinct domains and visualized by three-dimensional fluorescence in situ hybridization (3D-FISH) technique. The radial distribution of CTs is highly correlated with their gene densities and physical sizes. As an example, human 18 and 19 CTs show discrete difference in their positioning in lymphocyte nuclei; the gene-poor human 18 CTs are preferentially located at the nuclear periphery, while the gene-dense human 19 CTs are found in the nuclear interior. Here we investigated by 3D-FISH technique, 1) how radial distribution of CTs is evolutionarily conserved in primates, 2) how degree of relative positioning of CTs is involved in the evolutionary chromosomal translocations? First, we performed 3D-FISH analyses using the human 18 and 19 painting probes on the primate lymphocytes derived from various species, from chimpanzees, gibbons, Old World monkeys (6 species), and New World monkeys (5 species). The results showed that the topology of human 18 and 19 homologous CTs was highly conserved among those primate species. To study within the whole nuclear space, we developed the pooled chromosome paints specific for detecting the peripheral (P) or interior (I) nuclear space. The results by these probes also showed highly evolutionarily conserved even within the gibbon nuclei with highly evolutionary chromosomal rearrangements. Second, we used human chromosome 2p and 2q paints which is considered to be formed after fusing two separate acrocentric chromosomes, present in the great apes and Old World monkeys. Relative positioning of human 2p and 2q homologous CTs in primates showed the frequency with one pair chromosome kissing between 2p and 2q homologs is lower among the Old World monkeys but is higher among the great apes, suggesting that it has tendency with higher frequency of the chromosome kissing between 2p and 2q homologs among the evolutionary closed species from human.