High-throughput gene expression in soil invertebrate embryos – mechanisms of Cd toxicity in Enchytraeus crypticus

Gene expression can vary with the organisms' life stage. It is known that embryos can be more sensitive to toxicant exposure, as previously demonstrated for Enchytraeus crypticus (Oligochaeta) exposed to cadmium (Cd), known to cause embryotoxicity and hatching delay. It was shown that Ca enters embryos via the L-type Ca channels in the cocoon membrane, this being affected in Cd exposed embryos (Cd-Ca competition is well-known). In the present study, the embryotoxic mechanisms of Cd were studied via high-throughput gene expression for E. crypticus. Cocoons (1e2 days old), instead of the adult organism, were exposed in Cd spiked LUFA 2.2 soil during 1 day. Results showed that Cd affected Ca homeostasis which is implicated in several other molecular processes. Several of the major modulators of Cd toxicity (e.g., impaired gene expression, cell cycle arrest, DNA and mitochondrial damage) were identified in the embryos showing its relevancy as a model in ecotoxicogenomics. The draft Adverse Outcome Pathway was improved. Previously was hypothesized that gene regulation mechanisms were activated to synthesize more Ca channel proteins e this was confirmed here. Further, novel evidences were that, besides the extracellular competition, Cd competes intracellularly which causes a reduction in Ca efflux, and potentiates Cd embryotoxicity. Gene expression profile of Enchytraeus crypticus cocoons was analysed after 1 day of exposure to 5 and 16 mg Cadmium/kg soil, cadmium concentrations known to affect the embryonic development of E. crypticus. Three biological replicates per test treatment and control (un-spiked LUFA 2.2 soil) were used.