Sea urchin embryos as an in vivo model for the assessment of manganese toxicity: developmental and stress response effects

In the marine environment increasing concentrations of bio-available compounds often result from anthropogenic activities. Among metal ions, manganese represents a new emergent factor in environmental contamination. Here, we studied the effects of manganese on Paracentrotus lividus sea urchin embryos using biological and biochemical approaches for the analysis of impact on development, tissue accumulation and stress markers. Embryos were continuously exposed from fertilization to manganese at concentrations ranging from 1.0 to 61.6 mg l(-1), monitored for developmental abnormalities at 48 h after fertilization, and used for atomic spectrometric analysis at various times from 6 to 72 h. We found that concentration- and time-dependent increases in morphological abnormalities were directly correlated to manganese accumulation, with major defects in skeleton formation at 48 h. Concurrently, we found an upregulation of the hsc70 and hsc60 stress proteins detected by immunoblotting, whereas no induction of apoptosis or ROS production was observed by TUNEL and live tests, respectively. Taken together, our findings demonstrate that the observed manganese embryo-toxicity is related to both its intracellular accumulation and misregulated homeostasis, and confirm the importance of stress proteins as protective agents in the acquisition of tolerance and resistance to apoptosis.