A novel cluster of mariner-like elements belonging to mellifera subfamily from spiders and insects: implications of recent horizontal transfer on the South-West Islands of Japan

Mariner-like elements (MLEs) have been isolated from various eukaryotic genomes and they are divided into 15 subfamilies, including main five subfamilies: mauritiana, cecropia, mellifera/capitata, irritans, and elegans/briggsae. In the present study, MLEs belonging to mellifera subfamily were isolated from various spiders and insects (Hymenoptera and Lepidoptera) inhabiting the South-West Islands of Japan and neighboring regions. MLEs isolated from 15 different species formed a distinct novel cluster in mellifera subfamily. MLEs obtained from three different species [i.e., the bee Amegilla senahai subflavescens (Amsmar1), the wasp Campsomeris sp. (Casmar1), and the swallowtail butterfly Pachliopta aristolochiae (Paamar1)] contained an intact open reading frame that encoded a putative transposase. These transposases exhibited high similarity of 97.9 % among themselves. In case of Casmar1, the presence of an intact ORF was found in high frequencies (i.e., 11 out of 12 clones). In addition, these transposases also showed the presence of a terminal inverted repeat-binding motif, DD(34)D and two highly conserved amino acid motifs, (W/L)(I/L)PHQL and YSP(D/N)L(A/S)P. These two motifs differed from previously known motifs, WVPHEL and YSPDLAP. MLEs isolated from these three different species may have been inserted into their genomes by horizontal transfer. Furthermore, the presence of an intact ORF suggests that they are still active in habitats along these isolated islands.