Assessing coral stress responses using molecular biomarkers of gene transcription

We present a method for detecting rapid changes in coral gene expression at the messenger ribonucleic acid (mRNA) level. The staghorn coral Acropora cervicornis was exposed to 1 and 10 microg/L permethrin and 25 and 50 microg/L copper for 4 h. Using differential display polymerase chain reaction (PCR), mRNA associated with each toxicant exposure were reverse transcribed into complementary DNA (cDNA) fragments that were subsequently amplified and isolated. Six differentially expressed cDNA fragments were further developed into molecular probes that were used in Northern dot blots to determine the change in transcription levels of target transcripts. Changes in mRNA abundance were quantified by densitometry of chemiluminescence of digoxigenin-labeled probes hybridizing to target mRNA transcripts. The six gene probes showed varying degrees of sensitivity to the toxicants as well as specificity between toxicants. These probes were hybridized in Southern blots to genomic DNA from A. formosa sperm, which lacks zooxanthellae, to demonstrate that the genes coding for the mRNA transcripts produced are found within the coral genome. The gene probes developed in this study provide coral biologists with a new tool for coral assessment. Gene probes are sensitive, toxicant-specific biomarkers of coral stress responses with which gene sequence information can be obtained, providing a mechanism for identifying the stressor altering the gene expression.