Cellular reactions to sedimentation and temperature stress in the Caribbean coral Montastraea cavernosa

We present evidence of cellular responses to increased sedimentation and temperature in Montastraea cavernosa collected off Broward County, Florida. We sampled corals from six different sites approximately, 500-1000 m off shore, 10-15m depth. Six samples were collected from four sites adjacent to areas of underwater marine dredging (project sites), while the remaining two samples were obtained far away from the influence of the marine dredging (control sites). SSTs around collection time ranged 0.6-0.9 degrees C over the 40-year monthly mean. All specimens collected at project sites exhibited histopathological evidence of mild to moderate sedimentation stress including changes in size and number of mucocytes in epidermis and gastrodermis, attenuation of the epidermal and gastrodermal tissues, presence of cellular debris, and changes in number of zooxanthellae. These findings corroborate results of laboratory-based, sand-application experiments. In addition to the above-noted changes, one specimen exhibited multiple lesions consisting of unusual gastrodermal detachment with infiltration of amoebocytes into the adjacent mesoglea. Tissues surrounding detachment injuries exhibited marked to severe cellular changes. Accumulations of amoebocytes at lesion sites are seldom observed in wild corals. This response may be part of an organized reaction to injury and infection, as has been documented in sea anemones and gorgonians; however, further research is needed on the nature and role(s) of the scleractinian amoebocytes.     

Repopulation of Zooxanthellae in the Caribbean corals Montastraea annularis and M. faveolata following experimental and disease-associated bleaching.

Caribbean corals of the Montastraea annularis species complex associate with four taxa of symbiotic dinoflagellates (zooxanthellae; genus Symbiodinium) in ecologically predictable patterns. To investigate the resilience of these host-zooxanthella associations, we conducted field experiments in which we experimentally reduced the numbers of zooxanthellae (by transplanting to shallow water or by shading) and then allowed treated corals to recover. When depletion was not extreme, recovering corals generally contained the same types of zooxanthellae as they did prior to treatment. After severe depletion, however, recovering corals were always repopulated by zooxanthellae atypical for their habitat (and in some cases atypical for the coral species). These unusual zooxanthellar associations were often (but not always) established in experimentally bleached tissues even when adjacent tissues were untreated. Atypical zooxanthellae were also observed in bleached tissues of unmanipulated Montastraea with yellow-blotch disease. In colonies where unusual associations were established, the original taxa of zooxanthellae were not detected even 9 months after the end of treatment. These observations suggest that zooxanthellae in Montastraea range from fugitive opportunists and stress-tolerant generalists (Symbiodinium A and E) to narrowly adapted specialists (Symbiodinium B and C), and may undergo succession.     

Stable isotopic records of bleaching and endolithic algae blooms in the skeleton of the boulder forming coral Montastraea faveolata

Within boulder forming corals, fixation of dissolved inorganic carbon is performed by symbiotic dinoflagellates within the coral tissue and, to a lesser extent, endolithic algae within the coral skeleton. Endolithic algae produce distinctive green bands in the coral skeleton, and their origin may be related to periods of coral bleaching due to complete loss of dinoflagellate symbionts or “paling” in which symbiont populations are patchily reduced in coral tissue. Stable carbon isotopes were analyzed in coral skeletons across a known bleaching event and 12 blooms of endolithic algae to determine whether either of these types of changes in photosynthesis had a clear isotopic signature. Stable carbon isotopes tended to be enriched in the coral skeleton during the initiation of endolith blooms, consistent with enhanced photosynthesis by endoliths. In contrast, there were no consistent δ¹³C patterns directly associated with bleaching, suggesting that there is no unique isotopic signature of bleaching. On the other hand, isotopic values after bleaching were lighter 92% of the time when compared to the bleaching interval. This marked drop in skeletal δ¹³C may reflect increased kinetic fractionation and slow symbiont recolonization for several years after bleaching.     

Differential protein abundance during the first month of regeneration of the Caribbean star coral Montastraea cavernosa

It is critical to determine the methods by which coral colonies regenerate tissue lost to physical injury as they provide the physical structure of coral reef systems. To explore regeneration, circular lesions (12 mm diameter × 3 mm depth) were created in the fall of 2014 on 124 Montastraea cavernosa colonies located in the coastal waters of Grenada and Carriacou (10–12 m depth). Coral regeneration was documented at weekly intervals for 28 days. Repeated measures ANOVA on estimated weekly coral regeneration rates showed that island (p = 0.024) and colony colour (p = 0.024) were the only factors significantly affecting lesion regeneration. Mean rate of lesion closure during the first 28 days was approximately 2.8 mm² d⁻¹. Four identical circular lesions were created on 30 M. cavernosa colonies (Carriacou, 10–12 m depth) in the fall of 2015. One representative lesion created on each coral colony was re-sampled at each of 14, 21, and 32 or 33 days following injury, and coral tissue was flash-frozen. Tissues from 10 normally pigmented brown colonies were selected for proteomic analysis using tandem mass tags. The initial polyp sample, the day 14, and the final samples were used to quantify the difference in protein abundance as the lesions healed. In the tissue samples 6419 peptides were reliably identified, which corresponded to 906 unique proteins. During the first month of regeneration, 111 proteins were differentially abundant (p < 0.05) on at least one timepoint and of these, 11 were associated with regeneration. An additional 14 proteins were also identified that were differentially abundant (p < 0.05) and were associated with inflammation or antioxidant activity. This work demonstrates, for the first time, the differential abundance of proteins associated with regeneration in a scleractinian coral.

     

Interpreting the sign of coral bleaching as friend vs. foe

Coral bleaching is a major concern to researchers, conservationists and the general public worldwide. To date, much of the high profile attention for bleaching has coincided with major environmental impacts and for many the term coral bleaching is synonymously associated with coral mortality (so‐called ‘lethal’ bleaching episodes). While this synonymous association has undoubtedly been key in raising public support, it carries unfair representation: nonlethal bleaching is, and always has been, a phenomenon that effectively occurs regularly in nature as corals acclimatize to regular periodic changes in growth environment (days, seasons etc). In addition, corals can exhibit sublethal bleaching during extreme environmental conditions whereby mortality does not occur and corals can potentially subsequently recover once ambient environmental conditions return. Perhaps not surprisingly it is the frequency and extent of these non and sublethal processes that yield key evidence as to how coral species and reef systems will likely withstand environmental and thus climatic change. Observations of non and sublethal bleaching (and subsequent recovery) are arguably not as readily reported as those of lethal bleaching since (1) the convenient tools used to quantify bleaching yield major ambiguity (and hence high potential for misidentification) as to the severity of bleaching; and (2) lethal bleaching events inevitably receive higher profile (media) attention and so are more readily reported. Under‐representation of non and sublethal bleaching signs may over‐classify the severity of bleaching, under‐estimate the potential resilience of reefs against environmental change, and thus ultimately limit (if not depreciate) the validity and effectiveness of reef management policies and practices. While bleaching induced coral mortality must remain our key concern it must be better placed within the context of bleaching signs that do not result in a long‐term loss of reef viability.     

A Molecular Biomarker System for Assessing the Health of Coral (Montastraea faveolata) During Heat Stress

Using a novel molecular biomaker system (MBS), we assessed the physiological status of coral (Montastraea faveolata) challenged by heat stress by assaying specific cellular and molecular parameters. This technology is particularly relevant for corals because heat stress is thought to be an essential component of coral bleaching. This phenomenon is widely believed to be responsible for coral mortality worldwide, particularly during 1997–1998. Specific parameters of coral cellular physiology were assayed using the MBS that are indicative of a nonstressed or stressed condition. The MBS distinguished the separate and combined effects of heat and light on the 2 coral symbionts, a scleractinian coral and a dinoflagellate algae (zooxanthellae). This technology aids in the accurate diagnosis of coral condition because each parameter is physiologically well understood. Finally, the MBS technology is relatively inexpensive, easy to implement, and precise, and it can be quickly adapted to a high-throughout robotic system for mass sample analysis. Accepted May 25, 2000.     

Species-specific interactions between algal endosymbionts and coral hosts define their bleaching response to heat and light stress

The impacts of warming seas on the frequency and severity of bleaching events are well documented, but the potential for different Symbiodinium types to enhance the physiological tolerance of reef corals is not well understood. Here we compare the functionality and physiological properties of juvenile corals when experimentally infected with one of two homologous Symbiodinium types and exposed to combined heat and light stress. A suite of physiological indicators including chlorophyll a fluorescence, oxygen production and respiration, as well as pigment concentration consistently demonstrated lower metabolic costs and enhanced physiological tolerance of Acropora tenuis juveniles when hosting Symbiodinium type C1 compared with type D. In other studies, the same D-type has been shown to confer higher thermal tolerance than both C2 in adults and C1 in juveniles of the closely related species Acropora millepora. Our results challenge speculations that associations with type D are universally most robust to thermal stress. Although the heat tolerance of corals may be contingent on the Symbiodinium strain in hospite, our results highlight the complexity of interactions between symbiotic partners and a potential role for host factors in determining the physiological performance of reef corals.     

Global warming, regional trends and inshore environmental conditions influence coral bleaching in Hawaii

Hawaiian waters show a trend of increasing temperature over the past several decades that are consistent with observations in other coral reef areas of the world. The first documented large‐scale coral bleaching occurred in the Hawaii region during late summer of 1996, with a second in 2002. The bleaching events in Hawaii were triggered by a prolonged regional positive oceanic sea surface temperature (SST) anomaly greater than 1°C that developed offshore during the time of annual summer temperature maximum. High solar energy input and low winds further elevated inshore water temperature by 1–2°C in reef areas with restricted water circulation (bays, reef flats and lagoons) and in areas where mesoscale eddies often retain water masses close to shore for prolonged periods of time. Data and observations taken during these events illustrate problems in predicting the phenomena of large‐scale bleaching. Forecasts and hind‐casts of these events are based largely on offshore oceanic SST records, which are only a first approximation of inshore reef conditions. The observed oceanic warming trend is the ultimate cause of the increase in the frequency and severity of bleaching events. However, coral reefs occur in shallow inshore areas where conditions are influenced by winds, orographic cloud cover, complex bathymetry, waves and inshore currents. These factors alter local temperature, irradiance, water motion and other physical and biological variables known to influence bleaching.     

Comprehensive expression analysis of rice phospholipase D gene family during abiotic stresses and development

Phospholipase D is one of the crucial enzymes involved in lipid mediated signaling, triggered during various developmental and physiological processes. Different members of PLD gene family have been known to be induced under different abiotic stresses and during developmental processes in various plant species. In this report, we are presenting a detailed microarray based expression analysis and expression profiles of entire set of PLD genes in rice genome, under three abiotic stresses (salt, cold and drought) and different developmental stages (3-vegetative stages and 11-reproductive stages). Seven and nine PLD genes were identified, which were expressed differentially under abiotic stresses and during reproductive developmental stages, respectively. PLD genes, which were expressed significantly under abiotic stresses exhibited an overlapping expression pattern and were also differentially expressed during developmental stages. Moreover, expression pattern for a set of stress induced genes was validated by real time PCR and it supported the microarray expression data. These findings emphasize the role of PLDs in abiotic stress signaling and development in rice. In addition, expression profiling for duplicated PLD genes revealed a functional divergence between the duplicated genes and signify the role of gene duplication in the evolution of this gene family in rice. This expressional study will provide an important platform in future for the functional characterization of PLDs in crop plants.     

Corals escape bleaching in regions that recently and historically experienced frequent thermal stress

The response of coral-reef ecosystems to contemporary thermal stress may be in part a consequence of recent or historical sea-surface temperature (SST) variability. To test this hypothesis, we examined whether: (i) there was a relationship between the historical frequency of SST variability and stress experienced during the most recent thermal-stress events (in 1998 and 2005–2006) and (ii) coral reefs that historically experienced frequent thermal anomalies were less likely to experience coral bleaching during these recent thermal-stress events. Examination of nine detrended coral δ¹⁸O and Sr/Ca anomaly records revealed a high- (5.7-year) and low-frequency (>54-year) mode of SST variability. There was a positive relationship between the historical frequency of SST anomalies and recent thermal stress; sites historically dominated by the high-frequency mode experienced greater thermal stress than other sites during both events, and showed extensive coral bleaching in 1998. Nonetheless, in 2005–2006, corals at sites dominated by high-frequency variability showed reduced bleaching, despite experiencing high thermal stress. This bleaching resistance was most likely a consequence of rapid directional selection that followed the extreme thermal event of 1998. However, the benefits of regional resistance could come at the considerable cost of shifts in coral species composition.     

Large-amplitude internal waves benefit corals during thermal stress

Tropical scleractinian corals are particularly vulnerable to global warming as elevated sea surface temperatures (SSTs) disrupt the delicate balance between the coral host and their algal endosymbionts, leading to symbiont expulsion, mass bleaching and mortality. While satellite sensing of SST has proved a reliable predictor of coral bleaching at the regional scale, there are large deviations in bleaching severity and mortality on the local scale that are poorly understood. Here, we show that internal waves play a major role in explaining local coral bleaching and mortality patterns in the Andaman Sea. Despite a severe region-wide SST anomaly in May 2010, frequent upslope intrusions of cold sub-pycnocline waters due to breaking large-amplitude internal waves (LAIW) mitigated coral bleaching and mortality in shallow waters. In LAIW-sheltered waters, by contrast, bleaching-susceptible species suffered severe bleaching and total mortality. These findings suggest that LAIW benefit coral reefs during thermal stress and provide local refugia for bleaching-susceptible corals. LAIW are ubiquitous in tropical stratified waters and their swash zones may thus be important conservation areas for the maintenance of coral diversity in a warming climate. Taking LAIW into account can significantly improve coral bleaching predictions and provide a valuable tool for coral reef conservation and management.     

The RNA binding protein Musashi1 regulates apoptosis,gene expression and stress granule formation in urothelial carcinoma cells

The RNA‐binding protein Musashi1 (MSI1) is a marker of progenitor cells in the nervous system functioning as a translational repressor. We detected MSI1 mRNA in several bladder carcinoma cell lines, but not in cultured normal uroepithelial cells, whereas the paralogous MSI2 gene was broadly expressed. Knockdown of MSI1 expression by siRNA induced apoptosis and a severe decline in cell numbers in 5637 bladder carcinoma cells. Microarray analysis of gene expression changes after MSI1 knockdown significantly up‐regulated 735 genes, but down‐regulated only 31. Up‐regulated mRNAs contained a highly significantly greater number and density of Musashi binding sites. Therefore, a much larger set of mRNAs may be regulated by Musashi1, which may affect not only their translation, but also their turnover. The study confirmed p21^CIP1 and Numb proteins as targets of Musashi1, suggesting additionally p27^KIP1 in cell‐cycle regulation and Jagged‐1 in Notch signalling. A significant number of up‐regulated genes encoded components of stress granules (SGs), an organelle involved in translational regulation and mRNA turnover, and impacting on apoptosis. Accordingly, heat shock induced SG formation was augmented by Musashi1 down‐regulation. Our data show that ectopic MSI1 expression may contribute to tumorigenesis in selected bladder cancers through multiple mechanisms and reveal a previously unrecognized function of Musashi1 in the regulation of SG formation.     

大鼠成长期左心室基因表达谱的变化

为观察大鼠发育成熟过程中心脏生长与其基因表达谱变化的关系 ,应用超声心动术检测 8、10、12周龄Wistar大鼠的心脏结构和功能指标 ,应用cDNA基因芯片技术观察心脏基因表达水平的变化。大鼠从 8周龄生长至12周龄 ,体重增加约 45 7% ( 2 87± 13 gvs 197± 10g) ,前 2周和后 2周增加幅度相近。心脏左心室重量和室壁厚度分别增加约 2 7 7% ( 0 60± 0 0 3 gvs 0 47± 0 0 2 g)和 2 3 6% ( 2 0 4± 0 0 4mmvs 1 65± 0 13mm) ,前 2周增加幅度明显大于后 2周。基因表达谱的改变涉及细胞结构、代谢、氧化应激及信号转导等多方面的基因。 10周龄和 8周龄大鼠比较 ,变化的基因多数上调 ;12周龄和 10周龄大鼠比较 ,基因表达谱基本又返转至 8周龄水平。结果表明 ,大鼠在成长期的 4周内 ( 8- 12周龄 ) ,左心室基因表达谱发生的变化适应生理性心肌生长需要