Time-dependent transcriptomic responses of Daphnia magna exposed to metabolic disruptors that enhanced storage lipid accumulation.

Transcriptomic profiling of Daphnia magna samples exposed to tributyltin (TBT), pyriproxyfen (PP) and bisphenol A (BPA) at 8 and 24 hours. The analysis of lipid disruptive effects in invertebrates is limited by our poor knowledge of their lipidomes and of the associated metabolic pathways. Here we analyzed the subsequent transcriptome changes, using tributyltin (TBT), pyriproxyfen (PP) and bisphenol A (BPA). Changes in the whole transcriptome were assessed after 8 and 24 h of exposure, the period showing the greatest variation in storage lipid accumulation. The three compounds affected similarly to a total of 1388 genes (965 overexpressed and 423 underexpressed transcripts), but only after 24h of exposure. In addition,225 transcripts became up-regulated only in samples exposed to tributyltin for both 8h and 24 h. Using functional annotation from D. melanogaster, we determined that upregulated genes were enriched in members of KEGG modules implicated in fatty acid, phosphoinositol, glycerophospholipid, and glycerolipid metabolic pathways, as well as in genes related to membrane constituents , and to chitin and cuticle metabolic pathways. Conversely, down-regulated genes appeared mainly related with to visual perception, and to oocyte development signalling pathways. Many tributyltin specifically upregulated genes were related to neuro-active ligand receptor interaction signalling pathway. These changes are consistent with the previous observation that exposure of D. magna to the tested compounds increases lipid accumulation and reduces egg quality. In total, 24 samples were analysed. 12 samples corresponding to juveniles of Daphnia 8h after the exposure just after the third molt, including 3 control-solvent samples, 3 exposed to 1 mg/L of tributyltin, 3 exposed to 1 mg/L of pyriproxyfen and 3 exposed to 10 mg/L for bisphenol A; and 12 samples corresponding to juveniles of daphnia 24h after the exposure, including the same treatments mentioned before.