Response of holosymbiont pigments from the scleractinian coral Montipora monasteriata to short-term heat stress

Heating the scleractinian coral, Montipora monasteriata (Forskal 1775) to 32 degrees C under < 650 mu mol quanta m(-2) s(-1) led to bleaching in the form of a reduction in Peridinin, xanthophyll pool, chlorophyll c(2) and chlorophyll a, but areal dinoflagellates densities did not decline. Associated with this bleaching, chlorophyll (Chl) allomerization and dinoflagellate xanthophyll cycling increased. Chl allomerization is believed to result from the interaction of Chl with singlet oxygen (O-1(2)) or other reactive oxygen species. Thermally induced increases in Chl allomerization are consistent with other studies that have demonstrated that thermal stress generates reactive oxygen species in symbiotic dinoflagellates. Xanthophyll cycling requires the establishment of a pH gradient across the thylakoid membrane. Our results indicate that, during the early stages of thermal stress, thylakoid membranes are intact. Different morphs of M. monasteriata responded differently to the heat stress applied: heavily pigmented coral hosts taken from a high-light environment showed significant reductions in green fluorescent protein (GFP)-like homologues, whereas nonhost pigmented high-light morphs experienced a significant reduction in water-soluble protein content. Paradoxically, the more shade acclimated cave morph were, based on Chl fluorescence data, less thermally stressed than either of the high-light morphs. These results Support the importance of coral pigments for the regulation of the light environment within the host tissue.

Thapsigargin modulates osteoclastogenesis through the regulation of RANKL-induced signaling pathways and reactive oxygen species production

Introduction: Apoptosis and differentiation are among the consequences of changes in intracellular Ca2+ levels. In this study, we investigated the effects of the endoplasmic reticular Ca2+-ATPase inhibitor, thapsigargin (TG), on osteoclast apoptosis and differentiation. Materials and Methods: Both RAW264.7 cells and primary spleen cells were used to examine the effect of TG on RANKL-induced osteoclastogenesis. To determine the action of TG on signaling pathways, we used reporter gene assays for NF-kappa B and activator protein-1 (AP-1) activity, Western blotting for phosphoextracellular signal-related kinase (ERK), and fluorescent probes to measure changes in levels of intracellular calcium and reactive oxygen species (ROS). To assess rates of apoptosis, we measured changes in annexin staining, caspase-3 activity, and chromatin and F-actin microfilament structure. Results: At concentrations that caused a rapid rise in intracellular Ca2+, TG increased caspase-3 activity and promoted apoptosis in osteoclast-like cells (OLCs). Low concentrations of TG, which were insufficient to measurably alter intracellular Ca2+, unexpectedly suppressed caspase-3 activity and enhanced RANKL-induced osteoclastogenesis. At these lower concentrations, TG potentiated ROS production and RANKL-induced NF-kappa B activity, but suppressed RANKL-induced AP-1 activity and had little effect on ERK phosphorylation. Conclusion: Our novel findings of a biphasic effect of TG are incompletely explained by our current understanding of TG action, but raise the possibility that low intensity or local changes in subcellular Ca2+ levels may regulate intracellular differentiation signaling. The extent of cross-talk between Ca2+ and RANKL-mediated intracellular signaling pathways might be important in determining whether cells undergo apoptosis or differentiate into OLCs.