Combined Effects of Cadmium and UVB Radiation on Sea Urchin Embryos: Skeleton Impairment Parallels p38 MAPK Activation and Stress Genes Overexpression

Abstract

Human and natural activities release many pollutants in the marine environment. The mixture of pollutants can affect many organisms concurrently. We used Paracentrotus lividus as a model to analyze the effects on signal transduction pathways and stress gene expression in embryos exposed continuously to double stress, i.e., cadmium (Cd) from fertilization and UVB at cleavage (Cd/UVB-embryos). By microscopical inspection, we evaluated embryonic morphology after 72 h of development. Tissue-specific markers were used to assess mesoderm differentiation by immunofluorescence. We analyzed p38MAPK, ERK1/2, and JNK activation by Western blot and mRNA profiles of Pl-MT, Pl-14-3-3epsilon, and Pl-jun genes by real-time quantitative polymerase chain reaction (qPCR) and the localization of their transcripts by whole mount in situ hybridization (WMISH). We found that the Cd/UVB combined exposure induced morphological malformations in 76% of pluteus embryos, mainly affecting the development of the skeleton, including the normal branching of skeletal roads. In Cd/UVB-embryos, p38MAPK was activated 1 h after UVB exposure and a remarkable overexpression of the Pl-MT, Pl-14.3.3epsilon, and Pl-jun genes 24 h after UVB exposure. Pl-MT and Pl-14.3.3epsilon mRNAs were misexpressed as they were localized in a position different from that observed in wild-type embryos, i.e., the intestine. On the contrary, Pl-jun mRNA has remained localized in the skeletogenic cells despite their displacement in exposed embryos. In conclusion, Cd/UVB exposure affected skeletal patterning producing alternative morphologies in which p38MAPK activation and Pl-MT, Pl-14.3.3epsilon, and Pl-jun gene overexpression seem linked to a protective role against the stress response induced by Cd/UVB.