English: SEA URCHIN EMBRYO AS A MODEL TO EVALUATE THE STRESS RESPONSE ELICITED BY IONIZING RADIATION French: L'OURSIN COMME UN MODÈLE POUR ÉVALUER LA RÉPONSE AU STRESS INDUIT PAR LES RAYONNEMENTS IONISANTS

Introduction: The sea urchin embryo is a well - established model system used for classical embryology and for molecular eco-toxicological studies, to evaluate the effects of many harmful environmental chemicals (metals and physical stimuli (X-rays and UV radiation) as well as their combined action. Indeed, many studies have focused on the mechanisms adopted by sea urchin embryos to deal with UVR. Here, we used Paracentrotus lividus embryos to evaluate the stress response induced by X-rays at molecular level. Methods: Embryos were exposed to X-rays at doses ranging from 0.1 to 5Gray (Gy). Development was monitored at 24 and 48 hours post irradiation (hpi), when unexposed embryos were at gastrula and pluteus stages respectively. We also collected embryos exposed to the highest dose (5Gy) in order to analyze the accumulation levels of stress/anti -apoptotic proteins, such as HSP60, HSP70, BAG3 and p63, and to evaluate the mRNA levels of Pl-SM30 and Pl-msp130, two skeleton-specific genes. Results: We observed a dose-dependent increase of developmental delays and morphological defects in exposed embryos. In parallel, we measured a reduction in the mRNA levels of the two skeleton -specific genes, Pl-SM30 and Pl-msp130 and an increase in the HSP70, BAG3, and p63 protein levels only at 48hpi. No increase was detected in HSP60 protein levels. The levels of the mRNA coding for HSP70 and p63 were also investigated by relative RT-PCR and were found to increase at 24hpi, returning to their initial levels at 48hpi. These results suggest the presence of an adaptive regulatory mechanism operating at transcriptional (24hpi) and at translational (48hpi) levels. Conclusion: In conclusion, we propose the sea urchin embryo as a suitable ethical model for monitoring the effects of ionizing radiations such as X-rays for studying the protective pathways operating after irradiation. We acknowledge M.Biondo for technical assistance. Dedicated to the memory of V. Matranga