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The relative importance of DNA methylation and Dnmt2-mediated epigenetic regulation on Wolbachia densities and cytoplasmic incompatibility

ABSTRACT: Wolbachia pipientis is a worldwide bacterial parasite of arthropods that infects host germline cells and manipulates host reproduction to increase the ratio of infected females, the transmitting sex of the bacteria. The most common reproductive manipulation, cytoplasmic incompatibility (CI), is expressed as embryonic death in crosses between infected males and uninfected females. Specifically, Wolbachia modify developing sperm in the testes by unknown means to cause a post-fertilization disruption of the sperm chromatin that incapacitates the first mitosis of the embryo. As these Wolbachia-induced changes are stable, reversible, and affect the host cell cycle machinery including DNA replication and chromosome segregation, we hypothesized that the host methylation pathway is targeted for modulation during cytoplasmic incompatibility because it accounts for all of these traits. Here we show that infection of the testes is associated with a 55% increase of host DNA methylation in Drosophila melanogaster, but methylation of the paternal genome does not correlate with penetrance of CI. Overexpression and knock out of the Drosophila DNA methyltransferase Dnmt2 neither induces nor increases cytoplasmic incompatibility. Instead, overexpression decreases Wolbachia titers in host testes by approximately 17%, leading to a similar reduction in CI levels. Finally, strength of CI induced by several different strains of Wolbachia does not correlate with levels of DNA methylation in the host testes. We conclude that DNA methylation mediated by Drosophila's only known methyltransferase is not required for the transgenerational sperm modification that causes CI.

ORGANISM(S): Drosophila melanogaster

PROVIDER: GSE63795 | GEO | 2014/12/03

SECONDARY ACCESSION(S): PRJNA269080

REPOSITORIES: GEO

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Project description:The Drosophila-Wolbachia system is being used to study the molecular nature of the interactions between a host and a symbiont. This system offers a unique opportunity for such a study since the Drosophila genome sequence is available, several Wolbachi genomes will also be available soon and there are at least three known Wolbachia strains infecting Drosophila: a) mod+ strain that induces cytoplasmic incompatibility, b) mod- strain that cannot induce cytoplasmic incompatibility, and c) popcorn strain, a virulent strain which reduces in half the adult lifespan of Drosophila due to its massive proliferation in adult brain. The Drosophila-Wolbachia interaction manifests itself in 3 main ways; first, destruction of the CNS in infected adults, second, induction of some kind of modification or imprinting in the male germ-line resulting in an early failure in embryonic development, (cytoplasmic incompatability (CI)) and third, modification of the female germ-line resulting in resistance to modified sperm. We are interested in identifying Drosophila genes with changes in expression due to Wolbachia infection. We have generated a series of isogenic fly lines (those being used in the IGF P-element project) which we have infected with Wolbachia strains, infection is readily cured by growth on medium containing tetracycline. Thus, we have equivalent genetic background with and without the parasite. We have tested all of the transgenic lines for the level of CI and find strain-specific levels ranging from 0-50%. We also have a strain of D. simulans that shows over 95% CI. Plan: For our initial experiments we wish to make 4 comparisons, in all cases 2 day old males will be collected and for each comparison we will isolate 3 independent biological replicates: Melanogaster no CI [tet] x Melanogaster no CI [+wol] Melanogaster high CI [tet] x Melanogaster high CI [+wol] We will therefore identify genes with changed expression levels in the male upon Wolbachia infection by comparing the melanogaster strains with high or no CI in the presence of tetracycline and Wolbachia. We also hope to identify similar genes in simulans (where we expect the magnitude of the effect to be larger), differences between melanogaster and simulans are controlled for in the mel v sim comparison.

Project description:Globally invasive Aedes aegypti mosquitoes disseminate numerous arboviruses that impact human health. One promising method to control Ae. aegypti populations is transinfection with the intracellular bacterium Wolbachia pipientis, a symbiont that naturally infects ~40-52% of insects but is normally absent from Ae. aegypti. Transinfection of Ae. aegypti with the wMel Wolbachia strain induces cytoplasmic incompatibility (CI), allowing infected individuals to rapidly invade native populations. Further, wMel Wolbachia-infected females display refractoriness to medically relevant arboviruses. Thus, wMel Wolbachia-infected Ae. aegypti are being released in several areas to replace native populations, thereby suppressing disease transmission by this species. Wolbachia is reported to have minimal effects on Ae. aegypti fertility, but its influence on other reproductive processes is unknown. Female insects undergo several post-mating physiological and behavioral changes required for optimal fertility. Post-mating responses (PMRs) in female insects are typically elicited by receipt of male seminal fluid proteins (SFPs) transferred with sperm during mating, but can be modified by other factors, such as adult age, nutritional status, and microbiome composition. To assess how Wolbachia infection influences Ae. aegypti female PMRs, we collected wMel Wolbachia-infected Ae. aegypti from the field in Medellín, Colombia and introduced the bacterium into our laboratory strain. We found that Wolbachia influences female fecundity, fertility, and re-mating incidence. Further, we observed that Wolbachia significantly extends longevity of virgin females. Changes in female PMRs are not due to defects in sperm transfer by infected males, or sperm storage by infected females. Using proteomic methods to examine the seminal proteome of infected males, we found that Wolbachia infection has a moderate effect on SFP composition. However, we identified 125 Wolbachia proteins that are paternally transferred to females by infected males. Surprisingly, the CI factor proteins (Cifs), were not detected in the ejaculates of Wolbachia-infected males. Our findings indicate that Wolbachia infection of Ae. aegypti alters female post-mating responses, potentially influencing control programs that utilize Wolbachia-infected individuals.

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The relative importance of DNA methylation and Dnmt2-mediated epigenetic regulation on Wolbachia densities and cytoplasmic incompatibility

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