Identification of a telomere sequence type in three sponge species (Porifera) by fluorescence in situ hybridization analysis

The telomere sequence type (TTAGGG)(n) is known to be distributed in various phyla in the Animalia and in Mastigophora (Protista). However, the telomere type of Porifera (sponges), a phylum comprising the lowest multicellular animals, has not been reported. In this study, we examined the three sponge species Leucetta chagosensis, Halichondria japonica, and Halichondria panicea for the presence of the telomere type (TTAGGG)(n) by fluorescence in situ hybridization (FISH). The oligonucleotide probe (TTAGGG)(7) clearly displayed signals on the interphase nuclei of all three sponges. In contrast, the (TTAGG)(7) probe, which has one base fewer than (TTAGGG)(7), did not display the signals. These results suggest that the telomeres of the three sponges consist of (TTAGGG)(n), which is identical to the sequence type found in many higher multicellular animals and in Mastigophora. Additionally, this is the first study to reveal a telomere sequence type for Porifera. Moreover, these results suggest that Porifera are phylogenetically related to Mastigophora, and supports the general theory that Porifera evolved from Mastigophora. Further, this study strongly suggests that the origin of the (TTAGGG)(n) telomere sequence is to be found in a common ancestor of either the Bilateria and Porifera, or the Protista.