Ionizing radiation and stress response in sea urchin embryos used as model system

Classical embryology took advantage in the use of sea urchin embryo since 1900. More advanced molecular approachs defined the gene regulatory networks (GRNs) operating in early development. Nowadays, it is a well-established model system used for molecular eco-toxicological studies, to evaluate the effects of many harmful environmental chemical (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 cope with these agents using also high throughput molecular approachs. Here, we used Paracentrotus lividus embryos to evaluate the stress response induced by X-rays at molecular level. At early stage of development, embryos were exposed to X-rays at doses ranging from 0.1 to 5 Gray (Gy). Development was monitored at the endpoints of gastrula and pluteus stages, i.e. 24- and 48-hours post irradiation (hpi). We observed a dose-dependent increase of developmental delays and morphological defects in exposed embryos at both 24 and 48hpi. As skeleton was greatly impacted, by in situ hybridization and immunofluorescence we analyzed Pl-SM30 and Pl-msp130, two skeleton-specific genes. In addition, we found an increase in stress/anti-apoptotic proteins, such as the HSP70, BAG3, and p63 protein levels only at 48 hpi. No increase was detected in HSP60 protein levels. By relative RT-PCR, we found an increase in HSP70 and p63 mRNAs at 24hpi with a following decrease to their initial levels at 48hpi. These results demonstrate the presence of an adaptive regulatory mechanism operating at the transcriptional level at 24hpi, followed by a translational activation at 48hpi. 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. Dedicated to the memory of V. Matranga. MoMA Project (ASI, Contract 1/014/06/0) fully supported this work. Authors acknowledge the technical assistance of Mr. M. Biondo.