Colocalization of (TTAGGG)n telomeric sequences and ribosomal genes in Atlantic eels

Abstract

The distribution of (TTAGGG)n telomeric repeats was studied in chromosomes of two Atlantic eels, Anguilla anguilla and A. rostrata. We found that these sequences hybridize to all the telomeres but also to the entire nucleolar organizer region (NOR) localized in both species at the short arm of chromosome 8. This was considered to be due to the interspersion of telomeric sequences within the NOR ones. Whatever the significance of this interspersion may be, it seems to be limited to A. anguilla and A. rostrata since in Muraena helena (family muraenidae), which also belongs to the Anguilliformes, no telomeric hybridization signals were found along the NOR regions.

Genomic Organization Under Different Environmental Conditions:Hoplosternum Littoraleas a Model

“…81 This accumulation could explain the heteromorphism observed in the 5S rDNA and 18S rDNA sites in tamoatás, as previously observed in other fish and mammals. [82][83][84] Association between 18S rDNA and Rex3 are observed in the present study and can be related to dispersion of ribosomal sites, as have previously been observed in other Amazonian fish species. 12,85 Thus, probably 5S rDNA sites were duplicated and dispersed in the genome, since TEs are able to remove and insert themselves at other sites in the genome and are often duplicated during this process.…”

Localization of the (TTAGGG)n telomeric repeat in the chromosomes of the pufferfish Tetraodon fluviatilis (Hamilton Buchanan) (Osteichthyes)

“…In the at-lantic eels, Anguilla anguilla and A. rostrata (SALVADORI et al 1995) has been observed the presence of telomeric repeats interspersed within rDNA arrays and it has been hypothesised that such sequences could act as hotspot of recombination (ASHLEY and WARD 1993;SALVADORI et al 1995).…”

Interindividual size heteromorphism of NOR and chromosomal location of 5S rRNA genes in Iheringichthys labrosus

“…However, the visualization of 5S rDNA sites requires more specific techniques, such as fluorescence in situ hybridization (FISH). The fluorochromes that preferentially stain GCrich regions, such as mithramycin and chromomcyin A 3 (CMA 3 ), have also been widely used in chromosome preparations of fish to demonstrate the location of NORs, because according to Salvadori et al (1995), these regions are associated with DNA families rich in GC bases. More recently, FISH with rDNA probes has been utilized with precision to determine the exact location and number of ribosomal cístrons.…”