GSE54018
The extraembryonic serosa is a frontier epithelium providing the insect egg with a full-range innate immune response
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. Overall design: 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.