Effects of UV-B radiation on the development and hsp 70 expression in sea urchin cleavage embryos

A number of studies aimed to assess the health of aquatic ecosystems have focused on the dangerous effects of ultraviolet B (UV-B) radiation on marine organisms, especially those living in shallow waters such as sea urchin embryos and their larvae. We studied the effects of UV-B radiation on Paracentrotus lividus embryos at early stages of development, in laboratory experiments. Embryos at the 16-cell stage were exposed to different doses of UV-B, ranging from 10 to 800 J/m(2), and the resulting morphological abnormalities were observed. In addition, putative variations in the expression of the heat shock proteins 70 (hsp70) stress marker, at the protein and mRNA levels, were evaluated. The first effective dose was 150 J/m(2), producing a significant number of abnormal embryos, scored 24 h after exposure. This number increased up to 100% when the two highest doses were used (400 and 800 J/m(2)). Besides delays in embryonic development, the most abnormal morphology (abnormal blastula) consisted of blastula-like embryos, with cells unusually filling the blastocoelic cavity. Abnormal blastulae were not able to continue development as they were found 48 h after exposure. Some embryos with less severe abnormalities showed tri-radiate spicule rudiments, but had major defects in gut elongation. A corresponding dose-dependent increase in the hsp70 protein levels was observed in embryos exposed to different UV-B doses. Conversely, slight, if any variations were detected in the hsp70 mRNA levels for any of the doses tested, claiming for a post-transcriptional regulation of UV-B-induced stress response.