Cloning of molluscan telomere DNA with (TTAGGG)n repeat and its chromosomal location in the freshwater snail Biwamelania habei

In the present study, we have cloned and determined the nucleotide sequence of telomeric DNA of a freshwater gastropod Biwamelania habei. The sequence was comprised of (TTAGGG)n tandem repeat, which is identical with the sequ ence of vertebrate telomere. The characteristic sequences, together with th e chromosomal localization revealed by FISH analysis and the Bal 31 exonucl ease sensitivity of the hybridization signal, support the sequences to be l ocated at chromosomal ends. This is the first report for identification of molluscan telomere DNA and is also the first report of invertebrate telomer e with (TTAGGG)n sequence. Although the telomere sequence of B. habei is di fferent from that of any other invertebrates reported to date, the sequence universally occurs among various eukaryotes including some metazoans. It i s thus evident that a. habei retains ancestral sequence for invertebrate te lomeres. Interstitial telomeric signals were observed in some chromosomes. Some of such interstitial telomeric sites coincide with the presumed fusion point of Robertsonian rearrangement.