Sea urchin embryos as a model system for studying autophagy induced by cadmium stress

It is well known that sea urchin embryos are able to activate different defense strategies against stress. We previously demonstrated that cadmium treatment triggers the accumulation of metal in embryonic cells and the activation of defense systems depending on concentration and exposure time, through the synthesis of heat shock proteins and/or the initiation of apoptosis. Here we show that Paracentrotus lividus embryos exposed to Cd adopt autophagy as an additional stratagem to safeguard the developmental program. At present, there are no data focusing on the role of this process in embryo development of marine organisms. In this paper we utilized different techniques to detect autophagy in sea urchin embryos. Using neutral red (NR) and acridine orange (AO) vital staining, we found that embryos exposed to Cd display massive punctiform spots in the cytoplasm, indicative of acidic vesicular organelles (AVOs). These results have been confirmed using bafilomycin A1, a known inhibitor of this process. Furthermore these data were validated through both protein gel blotting and immunofluorescence in situ analysis of LC3-II, a specific marker of autophagy. We found that in P. lividus embryos autophagic processes occur in lesser amounts during physiological development and in greater amounts after Cd exposure