Effects of Hg(II) exposure on MAPK phosphorylation and antioxidant system in D. melanogaster.

The heavy metal mercury is a known toxin, but while the mechanisms involved in mercury toxicity have been well demonstrated in vertebrates, little is known about toxicological effects of this metal in invertebrates. Here, we present the results of our study investigating the effects associated with exposure of fruit fly Drosophila melanogaster to inorganic mercury (HgCl2 ). We quantify survival and locomotor performance as well as a variety of biochemical parameters including antioxidant status, MAPK phosphorylation and gene expression following mercury treatment. Our results demonstrate that exposure to Hg(II) through diet induced mortality and affected locomotor performance as evaluated by negative geotaxis, in D. melanogaster. We also saw a significant impact on the antioxidant system including an inhibition of acetylcholinesterase (Ache), glutathione S-transferase (GST) and superoxide dismutase (SOD) activities. We found no significant alteration in the levels of mRNA of antioxidant enzymes or NRF-2 transcriptional factor, but did detect a significant up regulation of the HSP83 gene. Mercury exposure also induced the phosphorylation of JNK and ERK, without altering p38(MAPK) and the concentration of these kinases. In parallel, Hg(II) induced PARP cleavage in a 89 kDa fragment, suggesting the triggering of apoptotic cell death in response to the treatment. Taken together, this data clarifies and extends our understanding of the molecular mechanisms mediating Hg(II) toxicity in an invertebrate model.

Paraquat administration in Drosophila for use in metabolic studies of oxidative stress.

Paraquat (PQ) is widely used in the laboratory to induce in vivo oxidative stress, particularly in the fruit fly, Drosophila melanogaster. PQ administration to the fly traditionally involves feeding in a 1% sucrose solution; however, a diet high in sucrose can itself be stressful. We examined a novel method of PQ administration: incorporation into the fly's standard cornmeal-sucrose-yeast diet. This method successfully delivers PQ to the fly at concentrations similar to those of the traditional method but with fewer possibly confounding complications.

Negative charge correlates with neural expression in vertebrate aldolase isozymes.

Electrophoretic studies suggest that negatively charged neural proteins are a general feature of jawed vertebrates. In an apparent example of this, teleost fish express three aldolase isozymes, one of which is expressed predominantly in neural tissues and is more negatively charged than its more generally expressed paralogues. We characterized three aldolase isozymes from a single species of teleost fish, zebrafish (Danio rerio). These sequences indicated that the correlation of net negative charge and neural expression suggested in other species by gel electrophoresis was supported by sequence analysis. When aldolase sequences from the databases were included in phylogenetic analyses, the negative charge/neural expression phenomenon was observed across the gnathostome vertebrate sequences examined. We found no evidence for a period of positive Darwinian selection resulting in an accumulation of negatively charged amino acids during the evolution of the neural aldolase isozymes. This is likely attributable, however, to limitations associated with the age of the duplication responsible for the neural isozyme and the reconstruction of ancestral sequences.