The IS630/Tc1/mariner transposons in three ctenophore genomes.

Transposable elements (TEs) exert a significant effect on the structure and functioning of the genomes and also serve as a source of the new genes. The study of the TE diversity and evolution in different taxa is indispensable for the fundamental understanding of their roles in the genomes. IS630/Tc1/mariner (ITm) transposable elements represent the most prevalent and diverse group of DNA transposons. In this work, we studied the diversity, evolutionary dynamics and the phylogenetic relationships of the ITm transposons found in three ctenophore species: Mnemiopsis leidyi, Pleurobrachia bachei, Beroe ovata. We identified 29 ITm transposons, seven of which possess the terminal inverted repeats (TIRs) and an intact transposase, and, thus, are, presumably, active. Four other ITm transposons have the features of domesticated TEs. According to the results of the phylogenetic analysis, the ITm transposons of the ctenophores represent five groups - MLE/DD34D, TLE/DD34-38E, mosquito/DD37E, Visiror/DD41D and pogo/DDxD. Pogo/DDxD superfamily turnes out to be the most diverse and prevalent, since it accounts for more than 40% of the TEs identified. The data obtained in this research will fill the gap of knowledge of the diversity and evolution of the ITm transposons in the multicellular genomes and will lay the ground for the study of the TE effects on the evolution of the ctenophores.