Transpositionally active episomal hAT elements

<p>Abstract</p> <p>Background</p> <p><it>hAT </it>elements and V(D)J recombination may have evolved from a common ancestral transposable element system. Extrachromosomal, circular forms of transposable elements (referred to here as episomal forms) have been reported yet their biological significance remains unknown. V(D)J signal joints, which resemble episomal transposable elements, have been considered non-recombinogenic products of V(D)J recombination and a safe way to dispose of excised chromosomal sequences. V(D)J signal joints can, however, participate in recombination reactions and the purpose of this study was to determine if <it>hobo </it>and <it>Hermes </it>episomal elements are also recombinogenic.</p> <p>Results</p> <p>Up to 50% of <it>hobo/Hermes </it>episomes contained two intact, inverted-terminal repeats and 86% of these contained from 1-1000 bp of intercalary DNA. Episomal <it>hobo/Hermes </it>elements were recovered from <it>Musca domestica </it>(a natural host of <it>Hermes</it>), <it>Drosophila melanogaster </it>(a natural host of <it>hobo</it>) and transgenic <it>Drosophila melanogaster </it>and <it>Aedes aegypti </it>(with autonomous <it>Hermes </it>elements). Episomal <it>Hermes </it>elements were recovered from unfertilized eggs of <it>M. domestica </it>and <it>D. melanogaster </it>demonstrating their potential for extrachromosomal, maternal transmission. Reintegration of episomal <it>Hermes </it>elements was observed <it>in vitro </it>and <it>in vivo </it>and the presence of <it>Hermes </it>episomes resulted in lower rates of canonical <it>Hermes </it>transposition <it>in vivo</it>.</p> <p>Conclusion</p> <p>Episomal <it>hobo</it>/<it>Hermes </it>elements are common products of element excision and can be maternally transmitted. Episomal forms of <it>Hermes </it>are capable of integration and also of influencing the transposition of canonical elements suggesting biological roles for these extrachromosomal elements in element transmission and regulation.</p

DNA binding activities of the Herves transposase from the mosquito Anopheles gambiae

Determining the mechanisms by which transposable elements move within a genome increases our understanding of how they can shape genome evolution. Class 2 transposable elements transpose via a 'cut-and-paste' mechanism mediated by a transposase that binds to sites at or near the ends of the transposon. Herves is a member of the hAT superfamily of class 2 transposons and was isolated from Anopheles gambiae, a medically important mosquito species that is the major vector of malaria in sub-Saharan Africa. Herves is transpositionally active and intact copies of it are found in field populations of A gambiae. In this study we report the binding activities of the Herves transposase to the sequences at the ends of the Herves transposon and compare these to other sequences recognized by hAT transposases isolated from other organisms. We identified the specific DNA-binding sites of the Herves transposase. Active Herves transposase was purified using an Escherichia coli expression system and bound in a site-specific manner to the subterminal and terminal sequences of the left and right ends of the element, respectively, and also interacted with the right but not the left terminal inverted repeat. We identified a common subterminal DNA-binding motif (CG/AATTCAT) that is critical and sufficient for Herves transposase binding. The Herves transposase binds specifically to a short motif located at both ends of the transposon but shows differential binding with respect to the left and right terminal inverted repeats. Despite similarities in the overall structures of hAT transposases, the regions to which they bind in their respective transposons differ in sequence ensuring the specificity of these enzymes to their respective transposon. The asymmetry with which the Herves terminal inverted repeats are bound by the transposase may indicate that these differ in their interactions with the enzyme.https://doi.org/10.1186/1759-8753-2-

The mosquito <it>Aedes aegypti </it>has a large genome size and high transposable element load but contains a low proportion of transposon-specific piRNAs

<p>Abstract</p> <p>Background</p> <p>The piRNA pathway has been shown in model organisms to be involved in silencing of transposons thereby providing genome stability. In <it>D. melanogaster </it>the majority of piRNAs map to these sequences. The medically important mosquito species <it>Aedes aegypti </it>has a large genome size, a high transposon load which includes Miniature Inverted repeat Transposable Elements (MITES) and an expansion of the piRNA biogenesis genes. Studies of transgenic lines of <it>Ae. aegypti </it>have indicated that introduced transposons are poorly remobilized and we sought to explore the basis of this. We wished to analyze the piRNA profile of <it>Ae. aegypti </it>and thereby determine if it is responsible for transposon silencing in this mosquito.</p> <p>Results</p> <p>Estimated piRNA sequence diversity was comparable between <it>Ae. aegypti </it>and <it>D. melanogaster</it>, but surprisingly only 19% of mosquito piRNAs mapped to transposons compared to 51% for <it>D. melanogaster</it>. <it>Ae. aegypti </it>piRNA clusters made up a larger percentage of the total genome than those of <it>D. melanogaster </it>but did not contain significantly higher percentages of transposon derived sequences than other regions of the genome. <it>Ae. aegypti </it>contains a number of protein coding genes that may be sources of piRNA biogenesis with two, <it>traffic jam </it>and <it>maelstrom</it>, implicated in this process in model organisms. Several genes of viral origin were also targeted by piRNAs. Examination of six mosquito libraries that had previously been transformed with transposon derived sequence revealed that new piRNA sequences had been generated to the transformed sequences, suggesting that they may have stimulated a transposon inactivation mechanism.</p> <p>Conclusions</p> <p><it>Ae. aegypti </it>has a large piRNA complement that maps to transposons but primarily gene sequences, including many viral-derived sequences. This, together the more uniform distribution of piRNA clusters throughout its genome, suggest that some aspects of the piRNA system differ between <it>Ae. aegypti </it>and <it>D. melanogaster</it>.</p

Extended in vivo transcriptomes of two ascoviruses with different tissue tropisms reveal alternative mechanisms for enhancing virus reproduction in hemolymph.

Ascoviruses are large dsDNA viruses characterized by the extraordinary changes they induce in cellular pathogenesis and architecture whereby after nuclear lysis and extensive hypertrophy, each cell is cleaved into numerous vesicles for virion reproduction. However, the level of viral replication and transcription in vesicles compared to other host tissues remains uncertain. Therefore, we applied RNA-Sequencing to compare the temporal transcriptome of Spodoptera frugiperda ascovirus (SfAV) and Trichoplusia ni ascovirus (TnAV) at 7, 14, and 21&nbsp;days post-infection (dpi). We found most transcription occurred in viral vesicles, not in initial tissues infected, a remarkably novel reproduction mechanism compared to all other viruses and most other intracellular pathogens. Specifically, the highest level of viral gene expression occurred in hemolymph, for TnAV at 7 dpi, and SfAV at 14 dpi. Moreover, we found that host immune genes were partially down-regulated in hemolymph, where most viral replication occurred in highly dense accumulations of vesicles

Highly Effective Broad Spectrum Chimeric Larvicide That Targets Vector Mosquitoes Using a Lipophilic Protein.

Two mosquitocidal bacteria, Bacillus thuringiensis subsp. israelensis (Bti) and Lysinibacillus sphaericus (Ls) are the active ingredients of commercial larvicides used widely to control vector mosquitoes. Bti's efficacy is due to synergistic interactions among four proteins, Cry4Aa, Cry4Ba, Cry11Aa, and Cyt1Aa, whereas Ls's activity is caused by Bin, a heterodimer consisting of BinA, the toxin, and BinB, a midgut-binding protein. Cyt1Aa is lipophilic and synergizes Bti Cry proteins by increasing midgut binding. We fused Bti's Cyt1Aa to Ls's BinA yielding a broad-spectrum chimeric protein highly mosquitocidal to important vector species including Anopheles gambiae, Culex quinquefasciatus, and Aedes aegypti, the latter an important Zika and Dengue virus vector insensitive to Ls Bin. Aside from its vector control potential, our bioassay data, in contrast to numerous other reports, provide strong evidence that BinA does not require conformational interactions with BinB or microvillar membrane lipids to bind to its intracellular target and kill mosquitoes

The mosquito Aedes aegypti has a large genome size and a high transposable element load but contains a low proportion of transposon-specific piRNAs.

Abstract Background The piRNA pathway has been shown in model organisms to be involved in silencing of transposons thereby providing genome stability. In D. melanogaster the majority of piRNAs map to these sequences. The medically important mosquito species Aedes aegypti has a large genome size, a high transposon load which includes Miniature Inverted repeat Transposable Elements (MITES) and an expansion of the piRNA biogenesis genes. Studies of transgenic lines of Ae. aegypti have indicated that introduced transposons are poorly remobilized and we sought to explore the basis of this. We wished to analyze the piRNA profile of Ae. aegypti and thereby determine if it is responsible for transposon silencing in this mosquito. Results Estimated piRNA sequence diversity was comparable between Ae. aegypti and D. melanogaster, but surprisingly only 19% of mosquito piRNAs mapped to transposons compared to 51% for D. melanogaster. Ae. aegypti piRNA clusters made up a larger percentage of the total genome than those of D. melanogaster but did not contain significantly higher percentages of transposon derived sequences than other regions of the genome. Ae. aegypti contains a number of protein coding genes that may be sources of piRNA biogenesis with two, traffic jam and maelstrom, implicated in this process in model organisms. Several genes of viral origin were also targeted by piRNAs. Examination of six mosquito libraries that had previously been transformed with transposon derived sequence revealed that new piRNA sequences had been generated to the transformed sequences, suggesting that they may have stimulated a transposon inactivation mechanism. Conclusions Ae. aegypti has a large piRNA complement that maps to transposons but primarily gene sequences, including many viral-derived sequences. This, together the more uniform distribution of piRNA clusters throughout its genome, suggest that some aspects of the piRNA system differ between Ae. aegypti and D. melanogaster