Project description:Drosophila larvae and adults possess a potent innate immune response, but the response of their eggs is particularly poor. Here we show that eggs of the beetle Tribolium castaneum, in contrast, possess a full range of immune defence mechanisms, based on complete transcriptome comparisons of naïve, sterilely injured, and bacterially challenged eggs. Upon infection, we find massive upregulation of AMPs and differential regulation of 375 other genes including both IMD and Toll signalling components. Importantly, we show that this extensive response depends on the serosa, an extraembryonic epithelium enveloping yolk and embryo. When we delete the serosa using Tc-zen1 RNAi, none of the AMPs and merely 57 other genes are differentially regulated upon infection. Furthermore, unchallenged eggs reveal serosa-biased expression of several bacterial recognition genes. Thus, the serosa is an immune competent frontier epithelium, and its loss in higher flies might account for the poor immune response of Drosophila eggs. Three different types of eggs were analysed. Wildtype eggs, eggs of which the mother was injected with a control dsRNA, and eggs without a serosa of which the mothers were injected with Tc-zen1 dsRNA. These three egg-types were subjected to three treatments, untreated (naïve), pricked with a sterile needle (sterile injury) and pricked with a mix of E.coli and M.luteus. This resulted in 9 samples which were all collected three times resulting in a total of 27 samples.
Project description:Drosophila larvae and adults possess a potent innate immune response, but the response of their eggs is particularly poor. Here we show that eggs of the beetle Tribolium castaneum, in contrast, possess a full range of immune defence mechanisms, based on complete transcriptome comparisons of naïve, sterilely injured, and bacterially challenged eggs. Upon infection, we find massive upregulation of AMPs and differential regulation of 375 other genes including both IMD and Toll signalling components. Importantly, we show that this extensive response depends on the serosa, an extraembryonic epithelium enveloping yolk and embryo. When we delete the serosa using Tc-zen1 RNAi, none of the AMPs and merely 57 other genes are differentially regulated upon infection. Furthermore, unchallenged eggs reveal serosa-biased expression of several bacterial recognition genes. Thus, the serosa is an immune competent frontier epithelium, and its loss in higher flies might account for the poor immune response of Drosophila eggs.
Project description:The unparalleled success of the insects comprising more than a million species has long stood out to evolutionary biologists. A much overlooked evolutionary innovation of the insects is the serosa, an extraembryonic epithelium that covers yolk and embryo in their eggs. We have shown that this epithelium provides innate immune protection to eggs of the beetle Tribolium castaneum. It remained elusive, however, if this innate immune competence evolved in the Tribolium lineage, or is ancestral to all insects. Here, we expand our studies to the bug Oncopeltus fasciatus that belongs to the basal main group of insects, the Hemimetabola. RNA sequencing reveals an extensive transcriptional response upon infection of the egg with Gram-positive and Gram-negative bacteria. We demonstrate the antimicrobial activity of upregulated peptides using in vitro bacterial growth inhibition assays, and describe two novel families of AMPs called Serosins and Ovicins. By qPCR, we determine that eggs become immune responsive when the serosa develops. Finally, in situ hybridizations show that transcripts of upregulated peptides are located in the serosal cells and not in the underlying embryo. We conclude that the serosa protects the O. fasciatus embryo against pathogens. This first evidence from hemimetabolous insect eggs suggests that immune competence is an ancestral property of the serosa. The evolutionary origin of the serosa with its immune function might have been one of the factors that facilitated the spectacular success of the insects.
Project description:In a number of species, individuals exposed to pathogens can mount an immune response and transmit this immunological experience to their offspring, thereby protecting them against persistent threats. Such vertical transfer of immunity, named trans-generational immune priming (TGIP), has been described in both vertebrates and invertebrates. Although increasingly studied during the last decade, the mechanisms underlying TGIP in invertebrates are still elusive, especially those protecting the earliest offspring life stage, i.e. the embryo developing in the egg. In the present study, we took the mealworm beetle Tenebrio molitor as a biological model, and combined different proteomic and transcriptomic approaches to determine whether mothers transfer a “signal” (such as fragments of infecting bacteria), mRNA and/or protein/peptide effectors to protect their eggs against two natural bacterial pathogens, namely the Gram-positive Bacillus thuringiensis (Bt) and the Gram-negative Serratia entomophila (Se). We demonstrated that eggs are mainly protected by an active direct transfer of a restricted number of immune proteins and of antimicrobial peptides. In contrast, the present data clearly reject the involvement of mRNA transfer while the transmission of a “signal”, if it happens, is marginal and only occurs within 24h after maternal exposure to bacteria. This work exemplifies the power of combining global multidisciplinary approaches to disentangle the different scenarios of a complex trait, providing a comprehensive characterization of TGIP mechanisms in T. molitor. It also paves the way for future alike studies focusing on TGIP in a wide range of invertebrates and vertebrates to identify additional candidates that could be specific to TGIP and to investigate whether the TGIP mechanisms found herein are specific or common to all insect species.