Cloning and characterization of Acmar1, a mariner-like element in the asiatic honey bee, Apis cerana japonica (Hymenoptera, Apocrita)

Diversity and Evolution of pogo and Tc1/mariner Transposons in the Apoidea Genomes

Bees (Apoidea), the largest and most crucial radiation of pollinators, play a vital role in the ecosystem balance. Transposons are widely distributed in nature and are important drivers of species diversity. However, transposons are rarely reported in important pollinators such as bees. Here, we surveyed 37 bee genomesin Apoidea, annotated the pogo and Tc1/mariner transposons in the genome of each species, and performed a phylogenetic analysis and determined their overall distribution. The pogo and Tc1/mariner families showed high diversity and low abundance in the 37 species, and their proportion was significantly higher in solitary bees than in social bees. DD34D/mariner was found to be distributed in almost all species and was found in Apis mellifera, Apis mellifera carnica, Apis mellifera caucasia, and Apis mellifera mellifera, and Euglossa dilemma may still be active. Using horizontal transfer analysis, we found that DD29-30D/Tigger may have experienced horizontal transfer (HT) events. The current study displayed the evolution profiles (including diversity, activity, and abundance) of the pogo and Tc1/mariner transposons across 37 species of Apoidea. Our data revealed their contributions to the genomic variations across these species and facilitated in understanding of the genome evolution of this lineage.

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.

Molecular characterization of mariner-like elements in emerald ash borer, Agrilus planipennis (Coleoptera, Polyphaga)

Emerald ash borer (EAB, Agrilus planipennis), an exotic invasive pest, has killed millions of ash trees (Fraxinus spp.) in North America and continues to threaten the very survival of the entire Fraxinus genus. Despite its high-impact status, to date very little knowledge exists for this devastating insect pest at the molecular level. Mariner-like elements (MLEs) are transposable elements, which are ubiquitous in occurrence in insects and other invertebrates. Because of their low specificity and broad host range, they can be used for epitope-tagging, gene mapping, and in vitro mutagenesis. The majority of the known MLEs are inactive due to in-frame shifts and stop codons within the open reading frame (ORF). We report on the cloning and characterization of two MLEs in A. planipennis genome (Apmar1 and Apmar2). Southern analysis indicated a very high copy number for Apmar1 and a moderate copy number for Apmar2. Phylogenetic analysis revealed that both elements belong to the irritans subfamily. Based on the high copy number for Apmar1, the full-length sequence was obtained using degenerate primers designed to the inverted terminal repeat (ITR) sequences of irritans MLEs. The recovered nucleotide sequence for Apmar1 consisted of 1,292 bases with perfect ITRs, and an ORF of 1,050 bases encoding a putative transposase of 349 amino acids. The deduced amino acid sequence of Apmar1 contained the conserved regions of mariner transposases including WVPHEL and YSPDLAP, and the D,D(34)D motif. Both Apmar1 and Apmar2 could represent useful genetic tools and provide insights on EAB adaptation.

Species sympatry and horizontal transfers of Mariner transposons in marine crustacean genomes

Mariner-like elements (MLEs) have been widely detected in terrestrial species. The first complete MLE isolated from a marine invertebrate was detected in the genome of the hydrothermal crab Bythograea thermydron by Halaimia-Toumi et al. [Halaimia-Toumi, N., Casse, N., Demattei, M.V., Renault, S., Pradier, E., Bigot, Y., Laulier, M., 2004. The GC-rich transposon Bytmar1 from the deep-sea hydrothermal crab, Bythograea thermydron, may encode three transposase isoforms from a single ORF. J. Mol. Evol. 59, 747-760] and called Bytmar1. Here, we report the isolation of three new Bytmar1 relatives from the genomes of one hydrothermal amphipod Ventiella sulfuris (Vensmar1) and two coastal crustacea, Maia brachydactila (Maibmar1) and Cancer pagurus (Canpmar1). Like Bytmar1, these MLEs have an unusually high GC content, a high CpG ratio, and a low TpA ratio. Their consensus sequence encodes a transposase that is preceded by an N-flag, as in Bytmar1, which could be a marine feature. Only one of the 19 clones obtained, Vensmar1.3, encoded for a full-length transposase. The phylogenetic analyses revealed that all these Bytmar1-related elements can be differentiated into two clusters, corresponding to the coastal or hydrothermal origin of their hosts. They also confirmed that the irritans sub-family comprises at least four lineages that seem to depend on the taxonomical position and habitat of their hosts. Finally, we observed that elements coding for two potentially complete transposases exhibiting 99.5% similarity, Bytmar1.11 and Vensmar1.3, were present in the genome of two distantly related hydrothermal crustacea, one Amphipod and one Decapod. The hypothesis of horizontal transfers is discussed in the light of the sequence similarities observed.

Detection of a mariner-like element and a miniature inverted-repeat transposable element (MITE) associated with the heterochromatin from ants of the genus Messor and their possible involvement for satellite DNA evolution

The satellite DNA of ants Messor bouvieri, M. barbarus and M. structor, studied in a previous paper, is organized as tandemly repeated 79-bp monomers in the three species showing high sequence similarity. In the present paper, a mariner-like element (Mboumar) and a new MITE (miniature inverted-repeat transposable element) called IRE-130, inserted into satellite DNA from M. bouvieri, are analyzed. The study of Mboumar element, of its transcription and the putative transposase that it would encode, suggests that it could be an active element. Mboumar elements inserted into IRE-130 elements have also been detected. It is the first time, to our knowledge, that a MITE has been described in Hymenoptera and it is also the first time that a mariner-like element inserted into a MITE has been detected. A mariner-like element, inserted into satellite DNA from M. structor and in M. barbarus, also has been found. The results seem to indicate that transposition events have participated in the satellite DNA mobilization and evolution.

The GC-rich transposon Bytmar1 from the deep-sea hydrothermal crab, Bythograea thermydron, may encode three transposase isoforms from a single ORF

Mariner-like elements (MLEs) are classII transposons with highly conserved sequence properties and are widespread in the genome of animal species living in continental environments. We describe here the first full-length MLE found in the genome of a marine crustacean species, the deep-sea hydrothermal crab Bythograea thermydron (Crustacea), named Bytmar1. A comparison of its sequence features with those of the MLEs contained in the genomes of continental species reveals several distinctive characteristics. First, Bytmar1 elements contains an ORF that may encode three transposase isoforms 349, 379, and 398 amino acids (aa) in long. The two biggest proteins are due to the presence of a 30- and 49-aa flag, respectively, at the N-terminal end of the 349-aa cardinal MLE transposase. Their GC contents are also significantly higher than those found in continental MLEs. This feature is mainly due to codon usage in the transposase ORF and directly interferes with the curvature propensities of the Bytmar1 nucleic acid sequence. Such an elevated GC content may interfere with the ability of Bytmar 1 to form an excision complex and, in consequence, with its efficiency to transpose. Finally, the origin of these characteristics and their possible consequences on transposition efficiency are discussed.

Germline transformation of the sawfly, Athalia rosae (Hymenoptera: Symphyta), mediated by a piggyBac-derived vector

A piggyBac construct carrying two green fluorescent protein (GFP)-coding sequences one driven by Bombyx mori actin gene promoter and the other by Drosophila melanogaster heat-shock protein 70 (hsp70) promoter were injected together with a nonautonomous helper plasmid containing an active piggyBac transposase gene into the posterior end of mature unfertilized eggs dissected from the ovaries of Athalia rosae (Hymenoptera: Symphyta). These injected eggs, which developed as haploid male embryos upon artificial activation, were cultured to adulthood. Of 278 injected eggs, 61 grew to G(0) haploid adult males. These G(0) haploid males were individually mated to diploid females. The progeny embryos (G(1) generation) were examined for GFP expression. Four GFP-positive embryos (from three independent G(0) matings) were obtained. Two eclosed as diploid adult G(1) females. Mature unfertilized eggs dissected from the GFP-positive G(1) diploid females were activated artificially, and the resultant embryos were examined for GFP expression, separated and cultured to adulthood (G(2) generation). The G(2) haploid embryos segregated to GFP-positive and -negative individuals. By mating the G(2) adult haploid males individually to diploid females, stocks were established in which the piggyBac construct was stably integrated into the genome, as evidenced by GFP expression and Southern blot hybridization. The piggyBac transposition occurred at its canonical target TTAA sequence. These results, which demonstrate the first successful stable transposon-mediated germline transformation in Hymenoptera, will expand the usefulness of the piggyBac vector.