Whole-arm chromosome rearrangements and telomeric signal displays: current cytogenetic updates on the examples of mammalian karyotype integrative variation.

Abstract

Introduction: Here we compare differences in the presence of telomeric signals (tDNA-FISH) among karyotypes of taxa having different whole-arm chromosomal rearrangements under the assumption of their participation in differentiation/integration processes during karyotype evolution. We analyzed cytogenetic peculiarities of Robertsonian-like (centromeric) and tandem (telomere-involving) rearrangements using examples of the authors' recent research on comparative cytogenetics of mammals. New data on intra- and interspecific karyotype variation helped to understand the nature of chromosomal rearrangements and their molecular features within and between species in two mammalian taxa: representatives of two genera from two orders (insectivores and rodents).

Methods: To detect telomeric repeats in karyotypes of representatives of the Eurasian genus Sorex and Ethiopian endemic Stenocephalemys, G-banded metaphase chromosomes were hybridized in situ with a fluorescein-conjugated peptide nucleic acid probe and 5-TAMRA-labeled (CCCTAA)4 oligonucleotides.

Results: We compared the location of a molecular chromosomal trait-telomeric sequences-among karyotypes of taxonomically distinct individuals having different types of whole-arm chromosomal rearrangements. Along with the regular terminal location of the telomeric signal on all chromosomes, displays of interstitial telomeric sequences (ITSs) were detectable. This pattern was typical for a studied shrew specimen whose karyotype corresponded to a natural interracial F1 hybrid. This finding doubles the number (known to date) of S. araneus race-specific metacentrics having an identified telomeric signal. In karyotypes of Stenocephalemys specimens, we revealed individual differences in autosomes corresponding to tandem fusion rearrangements, possibly species-specific, for the first time. No intrachromosomal telomeric signal expected in this case was detectable in autosomes, whereas we registered ITSs in pericentromeric regions on X chromosomes near a short, completely heterochromatic (additional) arm.

Conclusion: The new data indicates a heterogeneous distribution of the telomeric signal (tDNA-FISH) on mitotic chromosomes that are involved in (typical for mammals) whole-arm chromosomal variation, thus representing two models of karyotype evolution: Robertsonian polymorphism and tandem fusions. In the analyzed examples of whole-arm chromosomal rearrangements, displays of the centromeric ITS signal more likely represent an integral feature of cytogenetic relatedness within a species (chromosomal races) or between species (in a genus or group of genera) than differentiation of taxa.