Unknown,Transcriptomics,Genomics,Proteomics

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The extraembryonic serosa is a frontier epithelium providing the insect egg with a full-range innate immune response

ABSTRACT: 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 naÃ¯ve, 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 (naÃ¯ve), 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.

ORGANISM(S): Tribolium castaneum

SUBMITTER: Chris Jacobs

PROVIDER: E-GEOD-54018 | biostudies-arrayexpress |

REPOSITORIES: biostudies-arrayexpress

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Project description:We found that assassin bugs from the earliest-diverging subfamily of higher Reduviidae (Peiratinae), as well as a subfamily closely related to Triatominae (Stenopodainae) have venom that is highly similar in composition to that produced by previously examined reduviids from Harpactorinae and Reduviinae. This finding suggests that venom composition has been largely stable due to purifying selection among the higher Reduviidae, which is consistent with the ancient origin of venom in the ancestors of Heteroptera 250–300 million years ago (Sunagar and Moran 2015; Walker et al. 2018a). This near homogeneity of venom composition is perhaps surprising considering that reduviid predators have evolved numerous instances of prey specialization and specialized hunting strategies that might be expected to co-evolve with venom. Possibly, further studies focussing on species with more specialized hunting strategies, or different kinds of venom bioactivities, will uncover more nuanced venom adaptations. Alternatively, it is possible that the protease-rich venoms of predatory reduviids are simply well-suited to myriad different hunting strategies. These data are consistent with other examples where venoms are surprisingly similar despite great differences in biology, for example between solitary and eusocial bees. A more detailed picture of venom evolution in Reduviidae would examine venom produced by the early-diverging Phymatine complex as well as venoms of non-reduviid cimicomorphs, prey specialists such as the arachnophagous Emesinae and the myrmecophagous Holoptilinae, and some of the many groups that employ hunting specializations, such as the use of plant resins to catch prey (Hwang and Weirauch 2012). Within Triatominae, examination of saliva produced by additional species from multiple lineages (especially those that switched to blood-feeding independently, if the subfamily is shown to be polyphyletic) and including generalists and specialists on different host taxa and species associated especially with nests and burrows will be informative. The venoms of predatory reduviids such as Zelurus spp. and Opisthacidius spp. that are most closely related to Triatominae, and share some behaviours such as habitation of bird nests by Opisthacidius spp. may also provide more information about the evolution of triatomine saliva.

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The extraembryonic serosa is a frontier epithelium providing the insect egg with a full-range innate immune response

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