Heat Shock Protein 70 Expression in Juvenile Eastern Oysters, Crassostrea virginica (Gmelin, 1791), Exposed to Anoxic Conditions

Anoxic water events in conjunction with summer high temperatures are thought to be one of the causes of declines in natural oyster reefs on the eastern shore of Mobile Bay. Work is underway to determine whether tolerance to low oxygen can be selected for in hatchery-produced oysters. As a component of this work, the expression of heat shock protein 70 (HSP 70) was examined in control (normoxia) and anoxia-challenged juvenile oysters. Parental Eastern oysters, Crassostrea virginica were collected from 2 sites, Cedar Point Reef (CP), an area considered to have normoxic conditions, and White House Reef (WH), an area suspected to experience periodic anoxia. F1 generation oysters were produced from CP and WH parents that survived an anoxic exposure of 96 h. Control F1 generation oysters from both parental stocks not exposed to anoxia were also produced. The F1 generation oysters were subsequently exposed to anoxia or control normoxic conditions, and differences in expression of HSP 70 were examined. Nitrogen was used to create the anoxic conditions for both the parental and F1 generations. Three HSP 70 isoforms—2 constitutive forms (HSC 77 and HSC 72) and 1 inducible form (HSP 69)—were expressed in both anoxia- and normoxia-exposed oysters from all groups. Although there were differences among groups of oysters from the 2 sites, there were no differences in the expression of HSC 77 and HSC 72 between the control and anoxia-treated oysters within a group. Interestingly, the expression of HSP 69 was higher in oysters exposed to normoxia than the ones from anoxia treatments. These differences are thought to reflect a combination of responses to nutritional stress in the controls and facultative anaerobiosis and metabolic arrest in the anoxia groups