Localization of the repetitive telomeric sequence (TTAGGG)_nin four salmonid species

Abstract

We have analyzed the localization of the highly conserved telomeric sequence (TTAGGG)n in four salmonid species, two of the genus Salmo (Salmo trutta and Salmo salar) and two of the genus Oncorhynchus (Onchorhynchus mykiss and Onchorhynchus kisutch), by fluorescent in situ hybridization. As expected, the hybridization signal was mostly localized at the telomeres of all chromosomes in the four species. Two species evidenced special hybridization sites with the telomeric probe: (i) interstitial heterochromatic blocks in particular long chromosomes in S. salar; this observation supports tandem fusions as the karyotypic evolutionary mechanism leading to the formation of the long acrocentric and submetacentric chromosomes in the karyotype of S. salar; (ii) the whole NOR region in O mykiss; this observation suggests that the (TTAGGG)n sequence is scattered all along this chromosome region.

Genomic Distribution of Telomeric DNA Sequences – What Do We Learn from Fish About Telomere Evolution?

“…Consequently, too short internally located telomeric repeats may be below the resolution of the techniques enabling chromosomal location of DNA sequences. On the other hand, interstitial telomeric DNA sequences located far from the centromeric region have been detected in the Atlantic salmon large subtelocentric chromosomes, which supported hypothesis concerning tandem fusions as the mechanism leading to the formation of some of the chromosomes in this species (Abuin et al, 1996).…”

“…Robertsonian fusions, paracentric and pericentric inversions were suggested to be involved in changes leading to the establishment of the present karyotypes of three Coregonus species: European whitefish (Coregonus lavaraetus), vendace (Coregonus lavaretus) and peled (Coregonus peled) (Jankun et al, 2007). Unexpectedly, none of the cytogenetically studied salmonid fish species with fused meta-and submetacentric chromosomes showed pericentromeric locations of the telomeric repeats (Abuin et al, 1996;Jankun et al, 2007;Ocalewicz et al, 2008). The lack of ITS at the putative fusion sites in the bi-armed salmonid chromosomes may suggest p-arm telomeres were lost in the course of the chromosome breakage that preceded chromosome fusions.…”

“…Telomeric DNA sequences are observed to scatter along the heterochromatic NORs in the Atlantic eels (Anguilla anguilla) (Salvadori et al 1995), rainbow trout (Abuin et al, 1996), straight-nosed pipefish (Nerophis ophidion) (Libertini et al, 2006) and three mullet species (Mugilidae) (Sola et al, 2007). Such unusual distribution of TTAGGG repeats suggests telomeric sequences are interspersed with rDNA sequences.…”

Application of primed in situ DNA synthesis (PRINS) with telomere human commercial kit in molecular cytogenetics of Equus caballus and Sus scrofa scrofa.

“…The intrachromosomal telomeric repeats have been described in a variety of vertebrates ranging from mammals [24,35], birds [28], amphibian [36] to fishes [1]. The (TTAGGG)n sequence located between centromere and telomere can be the result of tandem chromosome fusion during evolution as well as the insertion of telomereic DNA within unstable sites during the repair of interstitial double-strand breaks [3,6,11,13].…”

In situ hybridization of bat chromosomes with human (TTAGGG)n probe, after previous digestion with Alu I

“…This repeated sequence has been detected not only in telomeres, but also in interstitial and centromeric chromosomal regions, in a variety of vertebrate species; in almost all of them, it is coincident with positive C-bands (Meyne et al, 1989(Meyne et al, , 1990Abuín et al, 1996;Vermeesch et al, 1996;Garagna et al, 1995;Ono and Yoshida 1997;Sharma and Sharma, 1998;Go et al, 2000;Pagnozzi et al, 2000). Although this association has not yet been clarified, there are suggestions that it might indicate that the sequence (T 2 AG 3 ) n is a component of the centromeric repeats (Metcalf et al, 1997(Metcalf et al, , 1998.…”