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Russian Journal of Theriology

The distributions of telomeric and ribosomal DNA on the chromosomes of two closely related species, Sorex araneus and Sorex granarius (Soricidae, Eulipotyphla) // Russian J. Theriol. Vol.6. No.1: 713 [in English].

ABSTRACT. It is widely believed that Robertsonian rearrangements have played a key role in the chromosome evolution of species of the Sorex araneus group. We present FISH data relating to the distribution of telomeric repeats and 18S rDNA on the chromosomes of Sorex araneus and Sorex granarius, which have karyotypes with almost identical chromosome arms. All chromosomes in S. araneus (Novosibirsk race) are metacentrics, whereas S. granarius has an acrocentric karyotype with two metacentric exceptions. In FISH experiments we revealed telomeric repeats at the ends of all S. araneus chromosomes but only on the short arms of S. granarius acrocentrics, which, as we have shown earlier, amount up to 300 kb in length. FISH signals of the (TTAGGG)n probe and the probe derived by microdissection of the pericentric regions of S. granarius acrocentrics a and b were co-localised or sequentially localised on distinct chromatin fibres of S. granarius. 18S rDNA clusters were found at the ends of short arms of 12 out of 16 S. granarius acrocentric pairs. In S. araneus primary cell culture fibroblasts rDNA was found at the ends of the q, t and u arms. However, after long cultivation of these cells an additional FISH signal of rDNA was found at the distal end of the o arm of chromosome go. In some regions the FISH signal of rDNA coincided with the signal of the telomeric probe. We suppose that rapid concerted evolution of telomeric and rDNA led to the repatterning of these repetitive DNA fractions in the sibling species S. araneus and S. granarius as well as the formation of large telomeres with unusual structure at the ends of the S. granarius chromosomes. KEY WORDS: Shrew chromosomes, FISH, large telomeres, ribosomal DNA.