Laboratory and field characterization of cellular and protein responses in the eastern oyster (Crassostrea virginica) under metal stress

The expression of the multitude of proteins comprising the protein complement of the genome (the proteome) of an organism varies according to internal and external conditions. Biological or toxicological stresses such as those induced by metal exposures within the environment, are among these conditions. In this dissertation research, the physiological conditions of the eastern oyster, Crassostrea virginica, exposed to the environmentally important toxicants, copper, cadmium, and zinc, were monitored and characterized using proteome analysis. The hypothesis tested in these projects was that key proteins of metal-exposed oysters are stable and persistent over time, across sites, across concentrations, across metals, and from the laboratory to the field. It was also hypothesized that these key proteins are specific to each metal and are directly related to cellular damage (measured as the breakdown of the lysosomes). To test this hypothesis, specific key proteins were characterized for each metal and were related to the duration of the exposure and each exposure concentration of each metal. These research projects were designed in three distinct yet interrelated phases. Phase I experiments demonstrated concentration-specific protein responses in the oyster exposed to metals as well as dose response and concentration effects at the cellular (lysosomal) and subcellular (protein) levels. Phase II experiments developed protein expression signatures (PESs) for each of the three metals (Cu, Cd, Zn) in the eastern oyster. The key proteins within these PESs consistently demonstrated metal specificity and provided evidence that key proteins, distinct from background variability, were specific to each individual toxicant. Key proteins were linked to biologically relevant effects, including lysosomal destabilization. Finally, Phase III experiments demonstrated the persistence of key proteins characterized in the laboratory in oysters transplanted in both contaminated and reference (control) field sites. When compared to laboratory-derived key proteins, partial persistence of key proteins for Cu, Cd, or Zn in oyster field samples from contaminated, natural environments were confirmed. Relationships therefore exist and have been demonstrated in these research projects between the presence of metal toxicants in the water and the expression of specific key proteins in the species Crassostrea virginica.