Abstract
We explored the topology of 18S and 28S rDNA units by fluorescence in situ hybridization (FISH) in the karyotypes of thirteen species representatives from major groups of Primates and Tupaia minor (Günther, 1876) (Scandentia), in order to expand our knowledge of Primate genome reshuffling and to identify the possible dispersion mechanisms of rDNA sequences. We documented that rDNA probe signals were identified on one to six pairs of chromosomes, both acrocentric and metacentric ones. In addition, we examined the potential homology of chromosomes bearing rDNA genes across different species and in a wide phylogenetic perspective, based on the DAPI-inverted pattern and their synteny to human. Our analysis revealed an extensive variability in the topology of the rDNA signals across studied species. In some cases, closely related species show signals on homologous chromosomes, thus representing synapomorphies, while in other cases, signal was detected on distinct chromosomes, leading to species specific patterns. These results led us to support the hypothesis that different mechanisms are responsible for the distribution of the ribosomal DNA cluster in Primates.
Highlights
Repetitive DNA elements make up a large portion of eukaryotic genomes and include tandem arrays and dispersed repeats
Discussion ribosomal DNA (rDNA) mapping has been previously performed in a number of Primate species (Table 2), but in pioneering studies, the cross-species homology of chromosomes with rDNA could not be reliably identified due to limitations of G-banding and the lack of advanced molecular cytogenetic methods, such as chromosome painting
The topology of rDNA loci was previously studied in Hylobates lar, Lemur catta and Symphalangus syndactylus (Warburton et al 1975, Henderson et al 1977, Hirai et al 1999), but at that time, it was not always possible to identify the hybridized chromosomes nor their homology with human chromosomes
Summary
Repetitive DNA elements make up a large portion of eukaryotic genomes and include tandem arrays and dispersed repeats. These genomic components are able to change the molecular composition of chromosomes and their study will contribute to the knowledge of karyotype differentiation (Cioffi et al 2010, Dumas et al 2017). The variation in number and topology of rDNA genes has been shown at inter- and intra-species levels, explained as consequence of chromosomal rearrangements, ectopic recombination through association of rDNA with other chromosomal segments during meiotic division or transposition events (Hirai et al 1996, Eickbush and Eickbush 2007, Baicharoen et al 2016)
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