527 ISSN 1990-519X, Cell and Tissue Biology, 2009, Vol. 3, No. 6, pp. 527–531. © Pleiades Publishing, Ltd., 2009. Original Russian Text © N.K. Galaktionov, O.I. Podgornaya, A.V. Fedorov, 2009, published in Tsitologiya, Vol. 51, No. 11, 2009, pp. 924–928. INTRODUCTION Mobile repeated elements compose a significant part of eukaryote genomes (Lander et al., 2001; Venter et al., 2001). The transposition of these sequences pro- duces a significant effect on the cell genome. The trans- position of mobile elements can modify gene expres- sion and lead to genome readjustments, specifically to the appearance of clonal variability (DeMarco et al., 2006). However, peculiarities of the organization and functioning of mobile elements in the genome have been poorly studied prior to now, which explains the necessity of choosing an adequate model system that includes both the transposon and the host organism, in which various actions of mobile elements in the genome would be realized. The question of the possible role of mariner trans- posons in the genetical variability of organisms also remains. The answer to this question can be obtained by studying the mariner element in the genome of a para- sitic organism that has a wide circle of hosts. The para- site host is perspective, as it enables the parallel study of the functioning of mobile elements in the parasite genome and their possible effect on genomes of host organisms. Therefore, to carry out the present study, the system represented by the parasitic flatworm Himasthla elongata (Trematoda, Echinostomatidae) and its hosts has been chosen. The life cycle of H. elongata alter- nates parthenogenetic and hermaphroditic generations in the wide circle of phylogenetically remote hosts. The free-living larva of the hermaphroditic generation, miracidium (Fig. 1(I)), enters the first intermediate host, i.e., Littorina littorea, L. obtusata, or L. saxatitis (Mollusca, Gastropoda), in which it is converted by metamorphosis into a maternal sporocyst and then to redia (Fig. 1(II)). Rediae produce free living larvae, i.e., cercariae, by parthenogenetic reproduction (Fig. 1(III)). Upon entering the second intermediate host, Mytilus edulis (Mollusca, Bivalvia), cercariae are incysted (Fig. 1(IV)) before entering the definitive host, Larus argentatus (Aves, Laridae), in which it is transformed to the hermaphroditic stage, i.e., marita (Fig. 1(V)). A necessary stage of studying the functions of mobile ele- ments in the presented system is the determination of the structural organization of transposons in the genome of H. elongata. This is of importance for both the determination of the parthenita clonal variability described for the related H. elogata species (Greveld- ing, 1999; Bayne et al., 2003) and from an evolutionary point of view. At present, the H. elongata genome is poorly studied and no mobile elements are revealed in its composition. The goal of this work is to detect and characterize the transposon of the mariner family in genome of the parasitic flatworm Himasthla elongata. The mariner mobile DNA element can serve a con- venient model for studying the functions of transposons in the genome. The mariner was first revealed in Droso- phila mauritiana (Jacobson et al., 1986) during a study of a mutation that was phenotypically accompanied by the formation of yellow-orange eye staining. DNA transposons of mariner have lengths of around 1.3 t.b.p.; are flanked by inverted repeats; and encode transposase, an enzyme that promotes the transposition of the mariner elements by the mechanism of cutting out–insertion (Miskey et al., 2005) (Fig. 2a). An analy- sis of the nucleotide and amino acid sequences of the mariner elements revealed in various species has shown that, in spite of the lack of a high (around 50%) Characterization of mariner Transposon from the Genome of Himasthla elongata Fluke N. K. Galaktionov, O. I. Podgornaya, and A. V. Fedorov Institute of Cytology, Russian Academy of Sciences, St. Petersburg, Russia e-mail: nikolai.galaktionov@gmail.com Received February 12, 2009 Abstract—A novel DNA-transposon Hemar1 has been identified and characterized in the genome of the flat- worm Himasthla elongata. This transposon is a representative of the mariner family, which is widely spread in eukaryotes; it belongs to the capitata subfamily and is highly homologous to the mariner element of the fresh- water turbellarian worm Dugesia tigrina. The Hemar1 transposon has been established as a dispersed repeat and accounts for about 0.01% of the H. elongata genome. The identified Hemar1 element is a convenient tool for the further study of the functioning of mobile elements in the H. elongata genome. Key words: DNA transposons, mariner , flatworms, parasitology. DOI: 10.1134/S1990519X09060042