Telomeres in Fishes

Abstract

In fishes, as in other vertebrate species, the DNA component of the telomeres consists of the tandemly repeated TTAGGG motif. The length of the telomeric arrays in fishes ranges from 2 to 25 kb and shortens with age in some of the species. To date, chromosomal distribution of the telomeric DNA sequences has been examined in approximately 80 fish species of which about 42% show additional telomeric hybridization signals far from the chromosomal termini. Based on the chromosomal location, such internally located telomeric repeats may be classified into 4 categories: (1) telomeric DNA sequences located at the pericentromeric regions, (2) interstitial telomeric sites observed between centromeres and the bona fide telomeres, (3) telomeric DNA sequences that scatter along the nucleolus organizer regions, and (4) telomeric DNA repeats interspersed with the entire chromosomes. Most of the pericentromeric and interstitial telomeric sequences in fish are possible relicts of chromosome fusion events. The origin of the telomeric sequences co- localizing with the major rDNA sequences or scattered along the whole chromosomes is not clear. Internally located telomeric repeats are considered as ‘hot spots' for recombination and thus may potentially increase the rates of chromosome breaks and rearrangements leading to the various chromosomal polymorphisms in fishes. FISH with telomeric probe applied to metaphase spreads of androgenetic specimens that hatched from eggs exposed to ionizing radiation before insemination enabled the detection of small radiation-induced fragments of maternal chromosomes. Remnants of the irradiated chromosomes were found to be ring chromosomes with the interstitial telomeric signals, telomerless rings, fragments with fused sister chromatids, and linear fragments with telomeres detected at both of their ends. The increasing availability of techniques enabling the study of fish telomeres and telomerase and the easy access to numerous fish species strongly confirm that these animals are promising models in research concerning the role of telomeres and telomerase in vertebrate aging, repair of ionizing radiation-induced DNA double strand breaks, and chromosomal rearrangements.

Chromosome Banding in Amphibia. XXXIV. Intrachromosomal Telomeric DNA Sequences in Anura

“…Further conspicuous ITSs have been discovered in primates [Garagna et al, 1997;Go et al, 2000;Farré et al, 2009], Carnivora [Wurster-Hill et al, 1988], Cetartiodactyla [Scherthan, 1990;Lee et al, 1993;Vermeesch et al, 1996], Perissodactyla [Santani et al, 2002], Chiroptera [Finato et al, 2000], Rodentia [Bertoni et al, 1996;Fagundes and Yonenaga-Yassuda, 1998;Castiglia et al, 2006;Ventura et al, 2006Ventura et al, , 2009Swier et al, 2012;Nagamachi et al, 2013], Marsupialia [Metcalfe et al, 1998[Metcalfe et al, , 2002[Metcalfe et al, , 2007Pagnozzi et al, 2000], birds Nanda et al, 2002Nanda et al, , 2007, reptiles [Schmid et al, , 2014aPellegrino et al, 1999Pellegrino et al, , 2009Bertolotto et al, 2001;Srikulnath et al, 2009;Rovatsos et al, 2015], amphibians ( table 1 ), and fishes [Abuín et al, 1996;Garrido-Ramos et al, 1998;Ocalewicz, 2013].…”

Cytogenetics of the Thorny Catfish <b><i>Trachydoras paraguayensis</i></b> (Eigenmann &amp; Ward, 1907), (Siluriformes, Doradidae): Evidence of Pericentric Inversions and Chromosomal Fusion

“…The chromosomal distribution of telomeric DNA sequences has been examined in ∼ 80 fish species, with 42% of them showing ITSs [Ocalewicz, 2013]. ITSs may be the result of (1) fusion of telomeres of 2 chromosomes; (2) fusion of an acentric fragment with the telomere of another chromosome; or (3) telomere-centromere rearrangements, in which telomeric sequences of one chromosome fuse with the centromere of another chromosome [Rossi et al, 1993].…”

In situ Localization of (GATA)n and (TTAGGG)n Repeated DNAs and W Sex Chromosome Differentiation in Parodontidae (Actinopterygii: Characiformes)

“…In this context, Schemberger et al [2011] inferred that chromosome variation in the family Parodontidae is mostly due to the movement of DNA satellite sequences and TEs. The presence of ITS in fusion points and/or translocations is an event relatively common in fish [Ocalewicz, 2013]. In numerous events of chromosome rearrangements, telomeres can be completely lost or in low copy numbers [Slijepcevic, 1998].…”

“…In fish, Ocalewicz [2013] reported that in 80 species the (TTAGGG)n sequence was localized in situ to the telomere, and 42% presented additional telomeric hybridization signals far from the chromosome end (internal or interstitial telomeric sites, ITS). The localization of these ITS confirmed Robertsonian fusions [Rosa et al, 2012;Traldi et al, 2013;Errero Porto et al, 2014], but ITS can also be inserted in interstitial positions by telomerase or transposed to repair the ruptures in double-stranded DNA [Nergadze et al, 2007].…”