Detection of interstitial telomeric sequences in the Arctic charr (Salvelinus alpinus) (Teleostei: Salmonidae)

Abstract

Highly polymorphic Arctic charr ( Salvelinus alpinus Linnaeus, 1758) chromosomes were studied using conventional and molecular methods. The diploid chromosome number in the studied individuals was 2n = 81 or 2n = 82, with a fundamental arm number (NF) = 100. These differences are due to Robertsonian fusions. Interindividual variation in the number and size of DAPI and CMA(3) positively stained chromatin sites was observed in studied specimens. In the case of two individuals, the subtelomeric region of the long arm (q) of the largest acrocentric chromosome (chromosome number 10) was positively stained by CMA(3) fluorochrome. Both primed in situ labelling (PRINS) and fluorescence in situ hybridization (FISH) revealed that this CMA(3)-positive region was flanked by telomeric sequences. Previously, the subterminal position of interstitial telomeric sequences located in the vicinity of the CMA(3)-positive guanine-rich chromatin have been described in two other Salvelinus species, brook trout ( Salvelinus fontinalis ) and lake trout ( Salvelinus namaycush ). Moreover, multichromosomal location and variation in size of CMA(3) bands have been observed in various Salvelinus taxa, including fishes with internally located telomeric sequences. These results suggest that relocation of CMA(3)-positive chromatin segments in these species may be facilitated by flanking interstitial telomeric sequences (ITSs).

Cytogenetic and histological studies of the brook trout, Salvelinus fontinalis (Mitchill), and the Arctic char, S. alpinus (L.) hybrids

“…Individuals from the brook trout broodstock are characterized by a diploid chromosome number (2n) and a chromosome arm number, FN (Fundamental Number), which are 84 and 100, respectively (Ocalewicz et al 2004). In the Arctic char individuals from Rutki broodstock, diploid chromosome number varies from 81 to 82 (FN = 100) (Pomianowski et al 2012). Brook trout eggs collected from four females were inseminated with the spermatozoa from one Arctic char male.…”

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

“…Other mechanisms leading to the ITS formation have been suggested in three Salvelinus species: lake trout (Salvelinus namaycush), brook trout (Salvelinus fontinalis) and the Arctic charr (Salvelinus alpinus) showing subterminal position of the interstitial telomeric sequences (Figure 1c-d) assigned to the vicinity of the CMA 3 positive GC-rich heterochromatin (Reed and Phillips, 1995;Ocalewicz et al, 2004b;Pomianowski et al, 2012). Guanine-rich chromosomal regions are involved in several rearrangements like transpositions, duplications and (or) translocations resulted in multichromosomal location and variation in size of CMA 3 positively stained chromatin in Salvelinus species (Phillips et al, 1988;Phillips and Ráb, 2001).…”

“…In the case of the Arctic char metaphase spreads showing extended chromatin, the non-telomeric fluorescent hybridization signal covered a longer stretch of the chromosome than the signal from the telomere position, however the interstitial signal was less intense. This observation suggested that telomeric regions and ITS might have different structures (Pomianowski et al, 2012). It is possible that telomeric DNA sequences were not the only component of the ITS region.…”

“…This could partially explain the high level of size and location polymorphisms of the heterochromatic regions in Salvelinus species (Phillips et al, 1988;Phillips and Ráb, 2001;Pomianowski et al, 2012). Moreover, chromosomes with unusual distribution of telomeric DNA sequences may be useful cytogenetic markers enabling identification of parental chromosomes in hybrid organisms.…”

“…Application of PRINS using (CCTAAA) 7 primer and PNA-FISH using telomeric probes revealed different intensity of the hybridization foci on fish chromosomes (Ocalewicz and Dobosz, 2008;Pomianowski et al, 2012). As the fluorescence intensity of the telomere hybridization focus reflects the length of the telomeric repeat sequence , the differences in the telomere hybridization signal intensity observed on different chromosomes are likely related to variations in their respective telomere lengths.…”