Wolbachia Endosymbionts Modify Drosophila Ovary Protein Levels in a Context-Dependent Manner

ABSTRACT Endosymbiosis is a unique form of interaction between organisms, with one organism dwelling inside the other. One of the most widespread endosymbionts is Wolbachia pipientis, a maternally transmitted bacterium carried by insects, crustaceans, mites, and filarial nematodes. Although candidate proteins that contribute to maternal transmission have been identified, the molecular basis for maternal Wolbachia transmission remains largely unknown. To investigate transmission-related processes in response to Wolbachia infection, ovarian proteomes were analyzed from Wolbachia-infected Drosophila melanogaster and D. simulans. Endogenous and variant host-strain combinations were investigated. Significant and differentially abundant ovarian proteins were detected, indicating substantial regulatory changes in response to Wolbachia. Variant Wolbachia strains were associated with a broader impact on the ovary proteome than endogenous Wolbachia strains. The D. melanogaster ovarian environment also exhibited a higher level of diversity of proteomic responses to Wolbachia than D. simulans. Overall, many Wolbachia-responsive ovarian proteins detected in this study were consistent with expectations from the experimental literature. This suggests that context-specific changes in protein abundance contribute to Wolbachia manipulation of transmission-related mechanisms in oogenesis. IMPORTANCE Millions of insect species naturally carry bacterial endosymbionts called Wolbachia. Wolbachia bacteria are transmitted by females to their offspring through a robust egg-loading mechanism. The molecular basis for Wolbachia transmission remains poorly understood at this time, however. This proteomic study identified specific fruit fly ovarian proteins as being upregulated or downregulated in response to Wolbachia infection. The majority of these protein responses correlated specifically with the type of host and Wolbachia strain involved. This work corroborates previously identified factors and mechanisms while also framing the broader context of ovarian manipulation by Wolbachia

Host Modulation of Cytoplasmic Incompatibility in Drosophila simulans

Wolbachia are one of the most widespread bacterial endosymbionts, infecting mites, crustaceans and filarial nematodes as well as about half of all insect species. The prevalence of Wolbachia in nature results from its ability to manipulate the host reproduction to favor the success of infected females. The best-known reproductive modification induced by Wolbachia is sperm-egg cytoplasmic incompatibility (CI). In CI, the sperm of Wolbachia-infected males cause embryonic lethality in crosses with uninfected females, which is attributed by paternal chromatin segregation defect in early mitotic divisions. The embryos of Wolbachia-infected females can “rescue” CI lethality, bringing the egg hatch rate similar to uninfected crosses. The underlying mechanism for rescue of CI remains largely untested. In this study we used a chemical feeding approach to test host cellular capacity to induce rescue of CI in Drosophila simulans. Chemical inhibitors were fed to uninfected females, and the resulting egg hatch rate was scored from CI crosses, associated with native (wRi) and transinfected (wMel) Wolbachia strains. We found that treatment with seven chemicals were able to significantly increase CI egg hatch rates associated with paternal wRi Wolbachia infection. These chemicals reputedly affect DNA integrity, cell cycle control and protein turnover, implicating these functions in CI suppression. Three of these chemical treatments, associated with DNA integrity and protein turnover, were also able to significantly increase CI egg hatch rates associated with paternal wMel Wolbachia infection. These results implicate DNA integrity as a focal aspect of rescue induction/ CI suppression across Wolbachia strains. The framework presented here can be applied to diverse, genetically intractable CI models. Further studies will enrich our knowledge about the underlying mechanisms of host reproductive manipulation by insect endosymbionts