Potential Indicators of Stress Response Identified by Expressed Sequence Tag Analysis of Hemocytes and Embryos from the American Oyster, Crassostrea virginica

A pilot program was initiated to identify genes from the American oyster, Crassostrea virginica, that are potentially involved in the stress response for use as bioindicators of exposure to environmental pollutants and to toxic and infectious agents. A PCR-based method was used to construct cDNA libraries from pooled embryos and the hemocytes of a single individual. A total of 998 randomly selected clones (expressed sequence tags, ESTs) were sequenced. Approximately 40% of the ESTs are novel sequences. Several potential biomarkers identified include an antimicrobial peptide, recognition molecules (lectin receptors), proteinases and proteinase inhibitors, and a novel metallothionein. Diversity analysis shows that 363 and 286 unique genes were identified from the hemocyte and embryo libraries, respectively, indicating that full-scale EST collection is a valuable approach for the discovery of new genes of potential significance in the molluscan stress response. Received May 11, 2001; accepted July 16, 2001