Autophagy as defence strategy against cadmium stress in Paracentrotus lividus embryos.

Sea urchin embryo is a developmental model that offers an excellent opportunity to investigate the possible adaptive response of cells exposed to different stress during differentiation. These embryos are able to respond to many stress by synthesizing a set of highly conserved proteins, the hsps and/or by activation of apoptosis. The exposure to cadmium trigger the accumulation of metal in embryo cells and the activation of both defence mechanisms depending on concentration and exposure time [1-4]. Recent experimental evidences demonstrate that by autophagy, a highly regulated mechanism that enhances cell survival under various environmental and cellular stress, the breakdown and recycling of macromolecules and organelles, in different cell types is possible [5]. Here we report that also in P. lividus embryos autophagic process occur, at lesser extent during physiological development and at greater levels after cadmium treatment. By Acridine Orange staining, we found that embryonic cells exposed to cadmium display green fluorescence in cytoplasm and nucleus, and show considerable red fluorescent dots in cytoplasm. This evidence suggests formation of acidic auto-phagolysosomal vacuoles. By Neutral Red vital staining, specific for acid compartments, including lysosomes, we obtained analogous results (see figure). These data have been sustained by anti- LC3 antibody detection, a specific marker of autophagy. Our results show the existence of autophagy in P. lividus embryos, suggesting that this process could be an additional defence strategy activated against cadmium stress.