Developmental abnormalities induced by Gadolinium causes a time-dependent miss-expression of regulative and structural genes in P. lividus sea urchin embryos

Abstract

Gadolinium (Gd) is a metal of the lanthanide series of the elements whose chelates are commonly used as contrast agents for magnetic resonance imaging. Its release into the aquatic milieu has posed serious concerns regarding its noxious effects, and therefore Gd is now considered an emerging environmental pollutant. The sea urchin embryo is an excellent model used in both toxicological and developmental research. We analysed the consequences of embryo exposure to sublethal concentrations of Gd on embryo development, focusing on skeletogenesis and developmental symmetry. We observed a strong inhibition of skeleton growth, frequently displayed by an asymmetrical pattern. Continuous exposure to Gd of sea urchin embryos caused autophagy, but not apoptosis. Results showed an increase of the LC3 protein at 24 and 48h, confirmed by the increased number of autophagosomes and autophagolysosomes observed by confocal microscopy. RT-PCR gene expression analysis showed the misregulation of several genes acting at different functional and hierarchical levels of both the skeletogenic and the left-right axis specification networks. These included: transcription factors (Alx-1, Nodal), signaling molecules (univin, VEGF, VEGF-R, FGF) and skeletal matrix proteins (p16, p19 and msp130). Embryos were exposed to the same Gd concetrantion and harvested at 6, 24 and 48 hrs post fertilization (hpf). After 24 hpf, Alx-1 and Nodal showed respectively 40% and 60% reduction of their relative transcriptional levels, while only Alx-1 was reduced by 60% at 48 hpf. A 50% reduction of univin, msp130 and p16 was found at 48 hpf, while FGF was reduced by 60%. Taken together, the results pose serious questions on the hazard of Gd in the marine environment and indicate that Gd is able to affect three different levels of the stress response in sea urchin embryos: morphogenesis, survival strategies such as autophagy, and gene expression.