Arachidonic acid and lysophosphatidylcholine inhibit multiple late steps of regulated exocytosis.

The canonical Phospholipase A2 (PLA2) metabolites lysophosphatidylcholine (LPC) and arachidonic acid (ARA) affect regulated exocytosis in a wide variety of cells and are proposed to directly influence membrane merger owing to their respective spontaneous curvatures. According to the Stalk-pore hypothesis, negative curvature ARA inhibits and promotes bilayer merger upon introduction into the distal or proximal monolayers, respectively; in contrast, with positive curvature, LPC has the opposite effects. Using fully primed, release-ready native cortical secretory vesicles (CV), well-established fusion assays and standardized lipid analyses, we show that exogenous ARA and LPC, as well as their non-metabolizable analogous, ETYA and ET-18-OCH3, inhibit the docking/priming and membrane merger steps, respectively, of regulated exocytosis.

Development of the sea urchin Heliocidaris crassispina from Hong Kong is robust to ocean acidification and copper contamination.

Metallic pollution is of particular concern in coastal cities. In the Asian megacity of Hong Kong, despite water qualities have improved over the past decade, some local zones are still particularly affected and could represent sinks for remobilization of labile toxic species such as copper. Ocean acidification is expected to increase the fraction of the most toxic form of copper (Cu2+) by 2.3-folds by 2100 (pH ≈7.7), increasing its bioavailability to marine organisms. Additionally, multiple stressors are likely to exert concomitant effects (additive, synergic or antagonist) on the organisms living in the sea. Here, we tested the hypothesis that copper-contaminated waters are more toxic to sea urchin larvae under future pH conditions. We exposed sea urchin embryos and larvae to two low-pH and two copper treatments (0.1 and 1.0 µM) in three separate experiments. Over the short time typically used for toxicity tests (up to 4-arm plutei, i.e. 3 days), larvae of the sea urchin Heliocidaris crassispina were robust and survived the copper levels present in Hong Kong waters today (≤0.19 µM) as well as the average pH projected for 2100. We, however, observed significant mortality with lowering pH in the longer, single-stressor experiment (Expt A: 8-arm plutei, i.e. 9 days). Abnormality and arm asymmetry were significantly increased by pH or/and by copper presence (depending on the experiment and copper level). Body size (d3; but not body growth rates in Expt A) was significantly reduced by both lowered pH and added copper. Larval respiration (Expt A) was doubled by a decrease at pHT from 8.0 to 7.3 on d6. In Expt B1.0 and B0.1, larval morphology (relative arm lengths and stomach volume) were affected by at least one of the two investigated factors. Although the larvae appeared robust, these sub-lethal effects may have indirect consequences on feeding, swimming and ultimately survival. The complex relationship between pH and metal speciation/uptake is not well-characterized and further investigations are urgently needed to detangle the mechanisms involved and to identify possible caveats in routinely used toxicity tests.

Gadolinium perturbs expression of skeletogenic genes, calcium uptake and larval development in phylogenetically distant sea urchin species.

Chelates of Gadolinium (Gd), a lanthanide metal, are employed as contrast agents for magnetic resonance imaging and are released into the aquatic environment where they are an emerging contaminant. We studied the effects of environmentally relevant Gd concentrations on the development of two phylogenetically and geographically distant sea urchin species: the Mediterranean Paracentrotus lividus and the Australian Heliocidaris tuberculata. We found a general delay of embryo development at 24h post-fertilization, and a strong inhibition of skeleton growth at 48h. Total Gd and Ca content in the larvae showed a time- and concentration-dependent increase in Gd, in parallel with a reduction in Ca. To investigate the impact of Gd on the expression of genes involved in the regulation of skeletogenesis, we performed comparative RT-PCR analysis and found a misregulation of several genes involved in the skeletogenic and left-right axis specification gene regulatory networks. Species-specific differences in the biomineralization response were evident, likely due to differences in the skeletal framework of the larvae and the amount of biomineral produced. Our results highlight the hazard of Gd for marine organisms.