Project description:This SuperSeries is composed of the following subset Series: GSE27022: Microarray studies of darkness stress and bleaching in the Caribbean coral Acropora palmata GSE27024: Microarray studies of darkness stress and bleaching in the Caribbean coral Montastraea faveolata Refer to individual Series
Project description:Projected elevation of seawater temperatures poses a threat to the reproductive success of Caribbean reef-building corals that have planktonic development during the warmest months of the year. This study examined the transcriptomic changes that occurred during embryonic and larval development of the elkhorn coral, Acropora palmata, at a non-stressful temperature (28°C) and further assessed the effects of two elevated temperatures (30°C and 31.5°C) on these expression patterns. Using cDNA microarrays, we compared expression levels of 2,051 genes from early embryos and larvae at multiple developmental stages (including pre-blastula, blastula, gastrula, and planula stages) at each of the three temperatures. At 12 hours post-fertilization in 28°C treatments, genes involved in cell replication/cell division and transcription were up-regulated in A. palmata embryos, followed by a reduction in expression of these genes during later growth stages. From 24.5 to 131 hours post-fertilization at 28°C, A. palmata altered its transcriptome by up-regulating genes involved in protein synthesis and metabolism. Temperatures of 30°C and 31.5°C caused major changes to the A. palmata embryonic transcriptomes, particularly in the samples from 24.5 hpf post-fertilization, characterized by down-regulation of numerous genes involved in cell replication/cell division, metabolism, cytoskeleton, and transcription, while heat shock genes were up-regulated compared to 28°C treatments. These results suggest that increased temperature may cause a breakdown in proper gene expression during development in A. palmata by down-regulation of genes involved in essential cellular processes, which may lead to the abnormal development and reduced survivorship documented in other studies.
Project description:Coral bleaching occurs in response to numerous abiotic stressors, the ecologically most relevant of which is hyperthermic stress due to increasing seawater temperatures. Bleaching events can span large geographic areas and are currently a potent threat to coral reefs worldwide. Much effort has been focused on understanding the molecular and cellular events underlying bleaching, and these studies have mainly utilized heat and light stress regimes. In an effort to determine whether different stressors share common bleaching mechanisms, we used cDNA microarrays for the corals Acropora palmata and Montastraea faveolata (containing > 10,000 features) to measure differential gene expression during darkness stress. This is the first coral microarray experiment aimed at darkness stress, and the first for these species to interrogate gene expression at such a large scale. Our results reveal a striking transcriptomic response to darkness in A. palmata involving chaperone and antioxidant up-regulation, growth arrest, and metabolic modifications. As these responses were also measured during thermal stress, our results suggest that different stressors may share common bleaching mechanisms. Furthermore, our results point to ER stress as a critical cellular event involved in darkness-specific (and possibly more general) molecular bleaching mechanisms. On the other hand, we identified a meager transcriptomic response to darkness in M. faveolata, where gene expression differences between host colonies and/or sampling locations were greater than differences between control and stressed fragments. To this end, we discuss the importance of factors related to host genotype, Symbiodinium genotype, and the abiotic environment that influence host gene expression and thereby can hinder an investigator’s ability to measure gene expression during a condition of interest.
Project description:The emergence of genomic tools for reef-building corals and symbiotic anemones comes at a time when alarming losses in coral cover are being observed worldwide. These tools hold great promise in elucidating novel and unforeseen cellular processes underlying the successful mutualism between corals and their algal endosymbionts (Symbiodinium spp.). Since thermal stress triggers a breakdown in the symbiosis (coral bleaching), measuring the transcriptomic response to thermal stress-induced bleaching offers an extraordinary view of the cellular processes specific to coral-algal symbioses. In the present study, we utilized a cDNA microarray containing 2,059 genes of the Caribbean Elkhorn coral Acropora palmata to identify genes differentially expressed upon thermal stress. Fragments from four separate colonies were exposed to elevated temperature (3˚C increase) for two days, and samples were frozen for microarray analysis after 24 and 48 hours. Fragments experienced a 60% reduction in algal cell density after two days. 204 genes were differentially expressed in samples collected one day after thermal stress; in samples collected after two days, 104 genes. Annotations of the differentially expressed genes indicate a conserved cellular stress response in A. palmata involving: 1) growth arrest; 2) chaperone activity; 3) nucleic acid stabilization and repair; and 4) the removal of damaged macromolecules. Other differentially expressed processes include sensory perception, metabolite transfer between host and symbiont, nitric oxide signaling, and modifications to the actin cytoskeleton and extracellular matrix. The results are also compared to those from a previous coral microarray study of thermal stress in Montastraea faveolata.
Project description:Coral bleaching occurs in response to numerous abiotic stressors, the ecologically most relevant of which is hyperthermic stress due to increasing seawater temperatures. Bleaching events can span large geographic areas and are currently a potent threat to coral reefs worldwide. Much effort has been focused on understanding the molecular and cellular events underlying bleaching, and these studies have mainly utilized heat and light stress regimes. In an effort to determine whether different stressors share common bleaching mechanisms, we used cDNA microarrays for the corals Acropora palmata and Montastraea faveolata (containing > 10,000 features) to measure differential gene expression during darkness stress. This is the first coral microarray experiment aimed at darkness stress, and the first for these species to interrogate gene expression at such a large scale. Our results reveal a striking transcriptomic response to darkness in A. palmata involving chaperone and antioxidant up-regulation, growth arrest, and metabolic modifications. As these responses were also measured during thermal stress, our results suggest that different stressors may share common bleaching mechanisms. Furthermore, our results point to ER stress as a critical cellular event involved in darkness-specific (and possibly more general) molecular bleaching mechanisms. On the other hand, we identified a meager transcriptomic response to darkness in M. faveolata, where gene expression differences between host colonies and/or sampling locations were greater than differences between control and stressed fragments. To this end, we discuss the importance of factors related to host genotype, Symbiodinium genotype, and the abiotic environment that influence host gene expression and thereby can hinder an investigator’s ability to measure gene expression during a condition of interest. We employed a reference design where all control and dark-stressed samples were compared to a pooled reference aRNA sample composed of aRNA from all fragments. Since all RNA samples were compared to the reference sample, direct comparisons of gene expression across all time points and conditions can be performed.
Project description:Projected elevation of seawater temperatures poses a threat to the reproductive success of Caribbean reef-building corals that have planktonic development during the warmest months of the year. This study examined the transcriptomic changes that occurred during embryonic and larval development of the elkhorn coral, Acropora palmata, at a non-stressful temperature (28°C) and further assessed the effects of two elevated temperatures (30°C and 31.5°C) on these expression patterns. Using cDNA microarrays, we compared expression levels of 2,051 genes from early embryos and larvae at multiple developmental stages (including pre-blastula, blastula, gastrula, and planula stages) at each of the three temperatures. At 12 hours post-fertilization in 28°C treatments, genes involved in cell replication/cell division and transcription were up-regulated in A. palmata embryos, followed by a reduction in expression of these genes during later growth stages. From 24.5 to 131 hours post-fertilization at 28°C, A. palmata altered its transcriptome by up-regulating genes involved in protein synthesis and metabolism. Temperatures of 30°C and 31.5°C caused major changes to the A. palmata embryonic transcriptomes, particularly in the samples from 24.5 hpf post-fertilization, characterized by down-regulation of numerous genes involved in cell replication/cell division, metabolism, cytoskeleton, and transcription, while heat shock genes were up-regulated compared to 28°C treatments. These results suggest that increased temperature may cause a breakdown in proper gene expression during development in A. palmata by down-regulation of genes involved in essential cellular processes, which may lead to the abnormal development and reduced survivorship documented in other studies. Our experimental setup followed a reference design where all samples were hybridized against the same pool made up of equal amounts of RNA from all samples in the experiment. Biological duplicate samples were used for each temperature at each developmental time period. Common reference samples were labeled with Cy3 dye, while temperature samples were labeled with Cy5 dye. Microarrays for A. palmata contained 2,051 coding sequences, of which 54.3% had functional annotations as determined by homology to known genes.