Localization of the pentanucleotide telomeric sequence (TTAGG)n in crustacean decapods

Localization of the pentanucleotide telomeric sequence (TTAGG)n in crustacean decapods. Coluccia E., Salvadori S., Deidda F., Cannas R., Deiana A.M. Dipartimento di Biologia Animale ed Ecologia, Università di Cagliari, V.le Poetto, 1- 09126 Cagliari, Italy. Telomeres are highly specialized DNA-protein structures that cap eukaryotic chromosome ends. They have a number of functions allowing complete replication at the end of a linear DNA molecule, preventing chromosomal degradation and end-to-end fusion. Although the sequence of the telomeric repeat differs among different organisms, some sequences are conserved in whole taxonomic groups; in fact the human telomere consensus sequence (TTAGGG)n is highly conserved among vertebrates, and the (TTTAGGG)n sequence is frequently found in plants. Telomeres of most invertebrate species have yet to be isolated, although among arthropods different types of telomere sequences have been reported, and the pentanucleotide (TTAGG) motif seems to be widespread among insects and present in other artropods, including crustaceans. In this study, fluorescence in situ hybridization (FISH) technique was used to determine the telomeric sequence in some species of lobsters belonging to the Palinuridae and Nephropidae families (Crustacea, Decapoda). Mitotic and meiotic chromosomes were prepared from gonads of adult males by the air-drying technique. Both the human TTAGGG repeat and the TTAGG repeat were used as probe. No hybridization signals were detected with the TTAGGG hexanucleotide repeated sequence; whereas strong signals were observed at the end of the chromosomes with the TTAGG pentanucleotide repeated sequence. These findings are in accordance with the hypotesis that the pentanucletide TTAGG is an ancestral motif of telomeres for arthropods. In fact the TTAGG repeat is widely conserved among insect species and hybridized to DNAs from other arthropods.