Differential gene expression during thermal stress and bleaching in the Caribbean coral Montastraea faveolata.

The declining health of coral reefs worldwide is likely to intensify in response to continued anthropogenic disturbance from coastal development, pollution, and climate change. In response to these stresses, reef-building corals may exhibit bleaching, which marks the breakdown in symbiosis between coral and zooxanthellae. Mass coral bleaching due to elevated water temperature can devastate coral reefs on a large geographical scale. In order to understand the molecular and cellular basis of bleaching in corals, we have measured gene expression changes associated with thermal stress and bleaching using a complementary DNA microarray containing 1310 genes of the Caribbean coral Montastraea faveolata. In a first experiment, we identified differentially expressed genes by comparing experimentally bleached M. faveolata fragments to control non-heat-stressed fragments. In a second experiment, we identified differentially expressed genes during a time course experiment with four time points across 9 days. Results suggest that thermal stress and bleaching in M. faveolata affect the following processes: oxidative stress, Ca(2+) homeostasis, cytoskeletal organization, cell death, calcification, metabolism, protein synthesis, heat shock protein activity, and transposon activity. These results represent the first medium-scale transcriptomic study focused on revealing the cellular foundation of thermal stress-induced coral bleaching. We postulate that oxidative stress in thermal-stressed corals causes a disruption of Ca(2+) homeostasis, which in turn leads to cytoskeletal and cell adhesion changes, decreased calcification, and the initiation of cell death via apoptosis and necrosis.

The antibody response in seabather's eruption.

Thirty-six of 44 patients with seabather's eruption had specific IgG antibodies against Linuche unguilata (thimble jelly) medusae antigen. ELISA detected antibodies in serum stored for 10 years. The extent of the cutaneous eruption or sting severity was correlated with antibody titer. Antibodies were detected in patients acquiring the eruption in Florida, the Bahamas and Aruba, reflecting the habitat of these jellyfish. This serological assay can be useful to confirm the clinical diagnosis.

Brevetoxin binding: molecular pharmacology versus immunoassay.

Brevetoxin PbTx-3 isolated from Florida's red tide dinoflagellate Ptychodiscus brevis has been produced recently in tritiated form by reductive tritiation of brevetoxin PbTx-2. Tritiated PbTx-3 has been used as a specific probe in competitive radioimmunoassays developed to detect brevetoxins in food sources, and this probe has also been utilized to characterize the brevetoxin binding component in rat brain synaptosomes. Brevetoxins PbTx-2 and PbTx-3, possessing the same structural backbone (type-1) as the tritiated probe, and PbTx-1 and PbTx-7, possessing a second structural backbone (type-2), have been compared quantitatively in their individual abilities to competitively displace tritiated PbTx-3 from its specific binding site in each assay. Type-1 toxins displaced labeled probe with ED50 values of 20-22 nM and 12-17 nM in radioimmunoassay and synaptosomes, respectively. Type-2 toxins displaced labeled probe with ED50 values of 92-93 nM and 3.5-4.1 nM in RIA and synaptosomes, respectively. Synaptosome assays reflect potency of each toxin examined, while radioimmunoassay reflects structural similarities to the immunizing toxin PbTx-3.

Biosynthesis of 'essential' amino acids by scleractinian corals.

Animals rely on their diet for amino acids that they are incapable either of synthesizing or of synthesizing in sufficient quantities to meet metabolic needs. These are the so-called 'essential amino acids'. This set of amino acids is similar among the vertebrates and many of the invertebrates. Previously, no information was available for amino acid synthesis by the most primitive invertebrates, the Cnidaria. The purpose of this study was to examine amino acid synthesis by representative cnidarians within the Order Scleractinia. Three species of zooxanthellate reef coral, Montastraea faveolata, Acropora cervicornis and Porites divaricata, and two species of non-zooxanthellate coral, Tubastrea coccinea and Astrangia poculata, were incubated with 14C-labelled glucose or with the 14C-labelled amino acids glutamic acid, lysine or valine. Radiolabel tracer was followed into protein amino acids. A total of 17 amino acids, including hydroxyproline, were distinguishable by the techniques used. Of these, only threonine was not found radiolabelled in any of the samples. We could not detect tryptophan or cysteine, nor distinguish between the amino acid pairs glutamic acid and glutamine, or aspartic acid and asparagine. Eight amino acids normally considered essential for animals were made by the five corals tested, although some of them were made only in small quantities. These eight amino acids are valine, isoleucine, leucine, tyrosine, phenylalanine histidine, methionine and lysine. The ability of cnidarians to synthesize these amino acids could be yet another indicator of a separate evolutionary history of the cnidarians from the rest of the Metazoa.

Heat Shock Protein Induction in Montastraea faveolata and Aiptasia pallida Exposed to Elevated Temperatures.

Frequent widespread episodes of coral bleaching have made researchers aware of the sensitivity of reef corals to moderately elevated temperatures and led us to investigate mechanisms of temperature stress tolerance in this group. One such mechanism may be the induced synthesis of heat shock proteins (hsps), which have been shown to play a role in thermotolerance in other organisms. However, induced synthesis of hsps in scleractinian corals was not reported until recently. Experiments were conducted in which Montastraea faveolata was exposed to high temperatures (up to 35{deg}C) for short periods (2 h). Under the conditions tested, the corals produced seven different hsps with approximate molecular weights of 95, 90, 78, 74, 33, 28, and 27 kDa. Another zooxanthellate species, the sea anemone Aiptasia pallida, also synthesized hsps during temperature stress, but fewer and with different molecular weights (82, 72, 68, and 48 kDa) than those produced by Montastraea. It now remains to be determined whether hsps are involved in differences in thermotolerance and susceptibility to bleaching within and between the various species of Montastraea, and between species of reef cnidarians.

Clinical perspectives on seabather's eruption, also known as 'sea lice'.

Seabather's eruption is usually a benign clinical syndrome that resolves spontaneously, although severe symptoms and long-term sequelae have been identified. Recent research has implicated the larvae of a jellyfish, Linuche unguiculata, as the cause of this syndrome; confirmation by serological and experimental studies is pending. Clinical signs and symptoms are consistent with this etiology. Outbreaks occur when jellyfish larvae are transported to shore by ocean currents. Treatment is symptomatic and involves use of antihistamines and steroids.