Abstract
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.
Highlights
Endocrine disrupting compounds (EDCs) are exogenous substances that interfere with hormone-regulated physiological processes and provoke adverse health effects in exposed organisms and/or their progeny[1]
In the present study, based on the GFOSS RNAseq-derived transcriptome database, we aimed to identify G. fossarum specific sequences homologue to key genes known to be involved in endocrine regulation of arthropods
As nuclear receptors are paralog genes with a highly evolutionary conserved domain called DNA-binding domain (DBD) and other conserved amino-acyl sequences in functional areas in the ligand-binding domain (LBD), the BLAST searches for RXR and EcR sequences yielded common results (Table 1)
Summary
Endocrine disrupting compounds (EDCs) are exogenous substances that interfere with hormone-regulated physiological processes and provoke adverse health effects in exposed organisms and/or their progeny[1]. Few proteins involved in hormonal regulation could be recognized from this database, and potential key candidates for ED biomarkers were not identified Such proteins are expected to be present at very low levels and are probably lost in the “background noise” of the proteome. Taking this context into account, we hypothesized that a gene candidate approach considering a thorough bioinformatics mining of the transcriptomic database obtained in G. fossarum could be used to identify candidate biomarkers of endocrine disruptor effects in this species. Early response genes are thought to be similar to those of insects[3,28,29]
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