Identification, expression, and endocrine-disruption of three ecdysone-responsive genes in the sentinel species Gammarus fossarum

Taking advantage of a large transcriptomic dataset recently obtained in the sentinel crustacean amphipod Gammarus fossarum, we developed an approach based on sequence similarity and phylogenetic reconstruction to identify key players involved in the endocrine regulation of G. fossarum. Our work identified three genes of interest: the nuclear receptors RXR and E75, and the regulator broad-complex (BR). Their involvement in the regulation of molting and reproduction, along with their sensitivity to chemical contamination were experimentally assessed by studying gene expression during the female reproductive cycle, and after laboratory exposure to model endocrine disrupting compounds (EDCs): pyriproxyfen, tebufenozide and piperonyl butoxide. RXR expression suggested a role of this gene in ecdysis and post-molting processes. E75 presented two expression peaks that suggested a role in vitellogenesis, and molting. BR expression showed no variation during molting/reproductive cycle. After exposure to the three EDCs, a strong inhibition of the inter-molt E75 peak was observed with tebufenozide, and an induction of RXR after exposure to pyriproxyfen and piperonyl butoxide. These results confirm the implication of RXR and E75 in hormonal regulation of female reproductive cycles in G. fossarum and their sensitivity towards EDCs opens the possibility of using them as specific endocrine disruption biomarkers.

Assessing the relevance of a multiplexed methodology for proteomic biomarker measurement in the invertebrate species Gammarus fossarum: A physiological and ecotoxicological study

Recently, a protein sequence database was built specifically for the sentinel non-model species Gammarus fossarum using a proteogenomics approach. A quantitative multiplexed targeted proteomics assay (using Selected Reaction Monitoring mass spectrometry) was then developed for a fast and simultaneous quantification of dozens of biomarker peptides specific of this freshwater sentinel crustacean species. In order to assess the relevance of this breakthrough methodology in ecotoxicology, the response patterns of a panel of 26 peptides reporting for 20 proteins from the Gammarus fossarum proteome with putative key functional roles (homeostasis, osmoregulation, nutrition, reproduction, molting,…) were recorded through male and female reproductive cycles and after exposure to environmental concentrations of cadmium and lead in laboratory-controlled conditions. Based on these results, we validated the implication of annotated vtg-like peptides in the oogenesis process, and the implication of Na⁺/K⁺ ATPase proteins in the molt cycle of organisms. Upon metal (cadmium and lead) contamination, peptides belonging to proteins annotated as involved in antioxidant and detoxification functions, immunity and molting were significantly down-regulated. Overall, this multiplex assay allowed gaining relevant insights upon disruption of different main functions in the sentinel species Gammarus fossarum. This breakthrough methodology in ecotoxicology offers a valid and high throughput alternative to currently used protocols, paving the way for future practical applications of proteogenomics-derived protein biomarkers in chemical risk assessment and environmental monitoring.