INTERSTITIAL TELOMERIC SITES IN NATIVE AND INVASIVE SPECIES OF CRUSTACEA DECAPODA

By definition, telomeric sequences are located at the chromosomal ends. Several eukaryotic species also show telomeric repeats in non-terminal regions, called interstitial telomeric sequences (ITSs). They might originate from ancestral intrachromosomal rearrangements, differential crossing-over or from the repair of double-strand break during evolution. ITSs could play a significant role in genome instability and evolution, they also might be hotspots of chromosome breakage, rearrangement and amplification sites. Crustacea Decapoda includes species of highly economical value, like lobsters, and of ecological interest such as the Louisiana crayfish, species became invasive in European freshwaters. Although a lot of genetic studies are available on this taxon, many phylogenetic and taxonomic aspects are still unclear. Cytogenetics, and in particular the localization of the telomeric sequence, could provide useful cytotaxonomic data, but very few species have been studied. Here, we examine the chromosomal location of telomeric repeats in 10 species of decapods belonging to different families in order to analyze the extent of ITSs occurrence in the chromosomes of representatives of this taxon. TTAGG telomeric repeat and 45S rDNA have been mapped by fluorescence in situ hybridization (FISH) on mitotic and meiotic chromosomes obtained from gonads and hepatopancreas of males by the air-drying technique. Beside terminal signals, detected in all species, in four of them several interstitial telomeric sites were present. These ITSs varied among different species in number and position and in some case were coincident with major ribosomal genes. Additionally, the invasive Louisiana crayfish Procambarus clarkii (Girard, 1852) presented two conspicuous and adjacent ITSs in one chromosome pair. It is remarkable the presence of ITs in almost 40% of the decapods studied, that suggests a intense chromosome dymanism in this group. In fact, ITs could be the remnant of chromosomal rearrangements, like tandem chromosome fusions, or might be associated with rDNA, satellite DNAs or transpsons, which could explain the interstitial distribution. Our results give new insights both for karyological comparative and cytogenomic analyses in crustacean decapods, underlying the relevance of this approach within this taxon. Study supported by the Fondazione di Sardegna (year 2016) and Regione Sardegna (LR 7/2007) for the project: Impact of Invasive Alien Species on Sardinian ecosystems.