Asymmetric skeleton patterns induced by gadolinium ions in sea urchin embryos: focus on mechanisms regulating skeletogenesis and comparison among phylogenetically distant species

Gadolinium (Gd) is a metal of the lanthanide series of the elements whose chelates are commonly employed as contrast agents for magnetic resonance imaging, and subsequently released into the aquatic environment. We analysed the consequences of embryo exposure to sublethal concentrations of Gd on development, focusing on skeletogenesis and developmental symmetry. We observed a strong inhibition of skeleton growth, frequently displayed by an asymmetrical pattern. Removal of Gd after 24 hours cause partial recovery of embryo development 48 hours post fertilization, demonstrating a reversible effect. Autophagy was investigated by Western blot analysis, showing an increase of the LC3 protein marker at 24h and 48h. Confocal microscopy studies confirmed the increased number of autophagosomes and autophagolysosomes, suggesting that the autophagic process is acting as a cell survival strategy. RT-PCR gene expression analysis showed the misregulation of several genes implicated in different functional levels of both the skeletogenic and the left-right axis specification networks. These included early expressed genes and signaling molecules acting upstream, as well as downstream skeletal structural genes. The comparison of the effects on phylogenetically distant sea urchin species confirmed that Gd highly perturbs skeletogenesis, with species- specific threshold levels of sensitivity. These results pose serious questions on the hazard of Gd in the marine environment.