Aiptasia Pallida Research Articles

The cellular basis of feeding-dependent body size plasticity in sea anemones.

Many animals share a lifelong capacity to adapt their growth rates and body sizes to changing environmental food supplies. However, the cellular and molecular basis underlying this plasticity remains only poorly understood. We therefore studied how the sea anemones Nematostella vectensis and Aiptasia (Exaiptasia pallida) respond to feeding and starvation. Combining quantifications of body size and cell numbers with mathematical modelling, we observed that growth and shrinkage rates in Nematostella are exponential, stereotypic and accompanied by dramatic changes in cell numbers. Notably, shrinkage rates, but not growth rates, are independent of body size. In the facultatively symbiotic Aiptasia, we show that growth and cell proliferation rates are dependent on the symbiotic state. On a cellular level, we found that >7% of all cells in Nematostella juveniles reversibly shift between S/G2/M and G1/G0 cell cycle phases when fed or starved, respectively. Furthermore, we demonstrate that polyp growth and cell proliferation are dependent on TOR signalling during feeding. Altogether, we provide a benchmark and resource for further investigating the nutritional regulation of body plasticity on multiple scales using the genetic toolkit available for Nematostella.

Starvation differentially affects gene expression, immunity and pathogen susceptibility across symbiotic states in a model cnidarian.

Mutualistic symbioses between cnidarians and photosynthetic algae are modulated by complex interactions between host immunity and environmental conditions. Here, we investigate how symbiosis interacts with food limitation to influence gene expression and stress response programming in the sea anemone Exaiptasia pallida (Aiptasia). Transcriptomic responses to starvation were similar between symbiotic and aposymbiotic Aiptasia; however, aposymbiotic anemone responses were stronger. Starved Aiptasia of both symbiotic states exhibited increased protein levels of immune-related transcription factor NF-κB, its associated gene pathways, and putative target genes. However, this starvation-induced increase in NF-κB correlated with increased immunity only in symbiotic anemones. Furthermore, starvation had opposite effects on Aiptasia susceptibility to pathogen and oxidative stress challenges, suggesting distinct energetic priorities under food scarce conditions. Finally, when we compared starvation responses in Aiptasia to those of a facultative coral and non-symbiotic anemone, 'defence' responses were similarly regulated in Aiptasia and the facultative coral, but not in the non-symbiotic anemone. This pattern suggests that capacity for symbiosis influences immune responses in cnidarians. In summary, expression of certain immune pathways-including NF-κB-does not necessarily predict susceptibility to pathogens, highlighting the complexities of cnidarian immunity and the influence of symbiosis under varying energetic demands.

Opinion 2500 (Case 3790) – Proposed review of Opinion 2404 and reconsideration of Case 3633: Dysactis pallida Agassiz in Verrill, 1864 (currently Exaiptasia pallida; Cnidaria, Anthozoa, Hexacorallia, Actiniaria): proposed precedence over Exaiptasia diaphana (Rapp, 1829) not approved

Opinion 2500 (Case 3790) – Proposed review of Opinion 2404 and reconsideration of Case 3633: Dysactis pallida Agassiz in Verrill, 1864 (currently Exaiptasia pallida; Cnidaria, Anthozoa, Hexacorallia, Actiniaria): proposed precedence over Exaiptasia diaphana (Rapp, 1829) not approved

Impact of rising seawater temperature on a phagocytic cell population during V. parahaemolyticus infection in the sea anemone E. pallida.

Climate change is increasing ocean temperatures and consequently impacts marine life (e.g., bacterial communities). In this context, studying host-pathogen interactions in marine organisms is becoming increasingly important, not only for ecological conservation, but also to reduce economic loss due to mass mortalities in cultured species. In this study, we used Exaiptasia pallida (E. pallida), an anemone, as an emerging marine model to better understand the effect of rising temperatures on the infection induced by the pathogenic marine bacterium Vibrio parahaemolyticus. The effect of temperature on E. pallida was examined at 6, 24, or 30 h after bath inoculation with 108 CFU of V. parahaemolyticus expressing GFP (Vp-GFP) at 27°C (husbandry temperature) or 31°C (heat stress). Morphological observations of E. pallida and their Hsps expression demonstrated heat stress induced increasing damage to anemones. The kinetics of the infections revealed that Vp-GFP were localized on the surface of the ectoderm and in the mucus during the first hours of infection and in the mesenterial filaments thereafter. To better identify the E. pallida cells targeted by Vp-GFP infection, we used spectral flow cytometry. E. pallida cell types were identified based on their autofluorescent properties. corresponding to different cell types (algae and cnidocytes). We identified an AF10 population whose autofluorescent spectrum was identical to that of human monocytes/macrophage, suggesting that this spectral print could be the hallmark of phagocytic cells called "amebocytes''. AF10 autofluorescent cells had a high capacity to phagocytize Vp-GFP, suggesting their possible role in fighting infection. This was confirmed by microscopy using sorted AF10 and GFP-positive cells (AF10+/GFP+). The number of AF10+/GFP+ cells were reduced at 31°C, demonstrating that increased temperature not only damages tissue but also affects the immune response of E. pallida. In conclusion, our study provides a springboard for more comprehensive studies of immune defense in marine organisms and paves the way for future studies of the dynamics, activation patterns, and functional responses of immune cells when encountering pathogens.

Coral Disease and Ingestion: Investigating the Role of Heterotrophy in the Transmission of Pathogenic Vibrio spp. using a Sea Anemone (Exaiptasia pallida) Model System.

Understanding disease transmission in corals can be complicated given the intricacy of the holobiont and difficulties associated with ex situ coral cultivation. As a result, most of the established transmission pathways for coral disease are associated with perturbance (i.e., damage) rather than evasion of immune defenses. Here, we investigate ingestion as a potential pathway for the transmission of coral pathogens that evades the mucus membrane. Using sea anemones (Exaiptasia pallida) and brine shrimp (Artemia sp.) to model coral feeding, we tracked the acquisition of the putative pathogens, Vibrio alginolyticus, V. harveyi, and V. mediterranei using GFP-tagged strains. Vibrio sp. were provided to anemones using 3 experimental exposures (i) direct water exposure alone, (ii) water exposure in the presence of a food source (non-spiked Artemia), and (iii) through a "spiked" food source (Vibrio-colonized Artemia) created by exposing Artemia cultures to GFP-Vibrio via the ambient water overnight. Following a 3 h feeding/exposure duration, the level of acquired GFP-Vibrio was quantified from anemone tissue homogenate. Ingestion of spiked Artemia resulted in a significantly greater burden of GFP-Vibrio equating to an 830-fold, 3,108-fold, and 435-fold increase in CFU mL-1 when compared to water exposed trials and a 207-fold, 62-fold, and 27-fold increase in CFU mL-1 compared to water exposed with food trials for V. alginolyticus, V. harveyi, and V. mediterranei, respectively. These data suggest that ingestion can facilitate delivery of an elevated dose of pathogenic bacteria in cnidarians and may describe an important portal of entry for pathogens in the absence of perturbing conditions. IMPORTANCE The front line of pathogen defense in corals is the mucus membrane. This membrane coats the surface body wall creating a semi-impermeable layer that inhibits pathogen entry from the ambient water both physically and biologically through mutualistic antagonism from resident mucus microbes. To date, much of the coral disease transmission research has been focused on mechanisms associated with perturbance of this membrane such as direct contact, vector lesions (predation/biting), and waterborne exposure through preexisting lesions. The present research describes a potential transmission pathway that evades the defenses provided by this membrane allowing unencumbered entry of bacteria as in association with food. This pathway may explain an important portal of entry for emergence of idiopathic infections in otherwise healthy corals and can be used to improve management practices for coral conservation.

Modeling food dependent symbiosis in Exaiptasia pallida

Cnidaria, marine invertebrates that include reef-building stony corals, often rely on photosynthetic endosymbionts to obtain the energy they need for growth. Increased temperatures and/or nutrient pollution can disrupt mutualistic properties of the symbiosis, leading to host mortality. However, the precise mechanism by which this dysbiosis occurs is still unclear. Sea anemones, other cnidarians that may host algal endosymbionts, are used as a model organism for the coral holobiont to understand the costs and benefits of symbionts, but the exact nature of the costs of symbionts on the hosts is still unclear. Here we developed a Dynamic Energy Budget (DEB) model and fit the model to data from the anemone Exaiptasia pallida and its endosymbiotic algae, Breviolum minutum, in order to identify the most likely mechanism of symbiont costs. In order to match the laboratory dataset, our model needed an explicit symbiont demand term, in which the symbiont can “consume” host tissue to forcibly extract nitrogen. The model demonstrates the role of the symbiont as an amplifier of the host’s state: a growing anemone grows better with symbionts, while a malnourished anemone looses biomass faster with a symbiont than without. This model allows us to project Cnidaria holobiont growth as a function of environmental conditions and adds a new framework for which to capture the direct cost a symbiont has on Cnidaria hosts.

Ni accumulation and effects on a representative Cnidaria - Exaiptasia pallida during single element exposure and in combination with Mn

Nickel (Ni) and manganese (Mn) are well known for the production of steel and alloys and are commonly found co-occurring in Ni ores. They are metals of environmental concern and contamination in the marine environment is problematic single exposures and in combination. Several studies have documented the effects of single metal exposure on the model anemone E. pallida, but research on the effects of metal mixtures is far less common. This novel study assesses the accumulation and stress effects of Ni and Mn over a 12-d exposure period. E. pallida were exposed in two separate experiments; Ni alone and Ni in combination with Mn, to assess accumulation, along with any effect on the density of symbionts and anemone tentacle length. Anemones were transferred to ambient seawater to assess depuration and recovery over 6 d. Anemone tissue accumulated Ni at a magnitude of five times higher in a mixture of 0.5 mg Ni/L with 2.5 mg Mn/L compared to the same concentration in a single Ni exposure experiment. In both experiments, Ni and Mn preferentially accumulated in the Symbiodinium spp. compared to the anemone tissue, but Ni depuration was more rapid in the mixture than Ni alone exposure. This study reveals a significant reduction in anemone Symbiodinium spp. density after exposure to Ni and Mn mixtures, but not with Ni exposure alone. A significant dose-dependent reduction in tentacle length was observed in anemones after 12 d of the Ni exposure both with and without Mn. The estimated sublethal concentration that causes tentacle retraction in 50% of test anemones (EC50) by Ni was 0.51 (0.25–0.73) mg/L, while in combination with Mn the EC50 was 0.30 mg Ni/L (confidence limits not calculatable). The present data reveals the importance of testing metal effects in combination before establishing safe limits for marine invertebrates.

Genome of the sea anemone Exaiptasia pallida and transcriptome profiles during tentacle regeneration.

Cnidarians including sea anemones, corals, hydra, and jellyfishes are a group of animals well known for their regeneration capacity. However, how non-coding RNAs such as microRNAs (also known as miRNAs) contribute to cnidarian tissue regeneration is poorly understood. Here, we sequenced and assembled the genome of the sea anemone Exaiptasia pallida collected in Hong Kong waters. The assembled genome size of E. pallida is 229.21 Mb with a scaffold N50 of 10.58 Mb and BUSCO completeness of 91.1%, representing a significantly improved genome assembly of this species. The organization of ANTP-class homeobox genes in this anthozoan further supported the previous findings in jellyfishes, where most of these genes are mainly located on three scaffolds. Tentacles of E. pallida were excised, and both mRNA and miRNA were sequenced at 9 time points (0 h, 6 h, 12 h, 18 h, 1 day, 2, 3, 6, and 8 days) from regenerating tentacles. In addition to the Wnt signaling pathway and homeobox genes that are shown to be likely involved in tissue regeneration as in other cnidarians, we have shown that GLWamide neuropeptides, and for the first time sesquiterpenoid pathway genes could potentially be involved in the late phase of cnidarian tissue regeneration. The established sea anemone model will be useful for further investigation of biology and evolution in, and the effect of climate change on this important group of animals.

Thermal Stress and Antioxidant Activity in Sea Anemones, Exaiptasia pallida

When exposed to stress, coral reefs undergo bleaching, a process in which the host‐symbiont relationship is disrupted. Stressors can be environmental including ocean acidification, exposure to ultraviolet radiation, or rising ocean temperatures due to global warming. The sea anemone, Exaiptasia pallida, serves as a model organism of coral reef biology since both species share symbiotic relationships with their algal symbionts and can undergo bleaching resulting in the expulsion of algal symbionts. This is the ultimate phenotypic result of high levels of stress experienced by the coral reef. Stress factors can lead to an increase in free radicals, like reactive oxygen species (ROS), that will adversely alter lipids, proteins, and DNA and trigger bleaching events. Although oxygen free radicals are natural by‐products of metabolic processes in most organisms, they are closely regulated through endogenous systems, such as antioxidants like superoxide dismutase (SOD). We hypothesized that as temperatures increase, the levels of SOD activity in the sea anemone will increase over time. We used commercially available E. pallida to establish a ‘stock’ aquaria to rear anemones under optimal conditions for at least two weeks before use. The stock aquaria were maintained at 28‐30% salinity at 22℃ during a 12‐hour light/dark period, at a pH of approximately 8.4, with low levels nitrate, nitrite, and ammonia (checked weekly). E. pallida were moved from the stock tank and placed into one of three identical tanks, maintained at increasing temperatures of 22℃ (control), 24℃, and 29℃. We sampled 5 anemones from each tank at two‐week intervals for 8 weeks. Seawater was removed by aspiration, anemones were weighed, flash‐frozen in liquid nitrogen, and stored at ‐80℃. We extracted proteins from each sample by homogenization on ice. For each sample, total protein concentrations were established with a Bradford assay and SOD concentration in units of activity was established with a commercially available SOD assay. By observation, the anemones reared at in the higher range of thermal stress appeared smaller and individuals tended to die faster during the trial. E. pallida reared under increased temperatures of 24℃ and 29℃ showed an increase in SOD activity from week 6 to week 8 compared to the control tank at 22℃. These data are based on two replicates and further trials are currently in progress. Our findings describe the outcome of elevated temperature on levels of metabolism and increased levels of superoxide dismutase activity as a byproduct of stress. In addition, disruption of a host‐symbiont relationship was suggested by the decrease in size and death of anemones at higher temperatures. Additional evidence is necessary to support our hypothesis and future experiments will focus on increasing the rearing time, increased temperatures, and other antioxidant defenses like xanthine oxidase or cyclooxygenases

Manganese uptake and partitioning between the tissue of the anemone host Exaiptasia pallida and Symbiodinium spp., including assessment of stress and recovery

Manganese (Mn) is essential for global steel and Mn-iron (Fe) alloy production. The human health effects of elevated Mn concentrations have been well established, but studies on its impact on marine invertebrates are limited. This study is the first to investigate Mn uptake in the sea anemone Exaiptasia pallida after chronic exposure (0.5, 1, 10, and 100 mg/L) for 24-d. Following exposure, E. pallida were transferred to ambient seawater for 6-d to assess Mn depuration. Mn accumulation and partitioning in host tissue and symbionts (Symbiodinium spp.), tentacle retraction, and symbiont cell density were measured during exposure and depuration. Mn concentrations were substantially higher in symbionts than tissue in all treatments after 24-d. No significant difference was observed for symbiont cell density after Mn exposure. Tentacle retractions were significantly higher in all Mn exposed treatments than controls at all time points. Mn depuration was observed for both tissue and symbionts but was more rapid in symbionts. This study reveals that Symbiodinium spp. can play a role in Mn uptake and depuration in anemones, but Mn loading does not affect cell density. These results help understand metal uptake and depuration in complex relationships between Symbiodinium spp. and other host taxa like corals.

Ni Uptake and Effects on a Representative Cnidaria - Exaiptasia Pallida During Single Element Exposure and in Combination with Mn

Ni Uptake and Effects on a Representative Cnidaria - Exaiptasia Pallida During Single Element Exposure and in Combination with Mn

Symbiosis maintenance in the facultative coral, Oculina arbuscula, relies on nitrogen cycling, cell cycle modulation, and immunity

Symbiosis with unicellular algae in the family Symbiodiniaceae is common across tropical marine invertebrates. Reef-building corals offer a clear example of cellular dysfunction leading to a dysbiosis that disrupts entire ecosystems in a process termed coral bleaching. Due to their obligate symbiotic relationship, understanding the molecular underpinnings that sustain this symbiosis in tropical reef-building corals is challenging, as any aposymbiotic state is inherently coupled with severe physiological stress. Here, we leverage the subtropical, facultatively symbiotic and calcifying coral Oculina arbuscula to investigate gene expression differences between aposymbiotic and symbiotic branches within the same colonies under baseline conditions. We further compare gene ontology (GO) and KOG enrichment in gene expression patterns from O. arbuscula with prior work in the sea anemone Exaiptasia pallida (Aiptasia) and the salamander Ambystoma maculatum—both of which exhibit endophotosymbiosis with unicellular algae. We identify nitrogen cycling, cell cycle control, and immune responses as key pathways involved in the maintenance of symbiosis under baseline conditions. Understanding the mechanisms that sustain a healthy symbiosis between corals and Symbiodiniaceae algae is of urgent importance given the vulnerability of these partnerships to changing environmental conditions and their role in the continued functioning of critical and highly diverse marine ecosystems.

N-Acetyl Neuraminic Acid (NANA) Activates L-Type Calcium Channels on Isolated Tentacle Supporting Cells of the Sea Anemone (Aiptasia pallida).

AbstractSensory receptors control nematocyst discharge on sea anemone tentacles. Micromolar N-acetylated sugars (e.g., N-acetyl neuraminic acid [NANA]) bind chemoreceptors on ectodermal supporting cells and predispose adjacent nematocyst discharge in response to mechanical contact via a cyclic adenosine monophosphate (cAMP)-dependent sensitization pathway, while higher NANA levels dose-dependently desensitize. Recent evidence implicates L-type calcium channels in desensitizing the pathway in aconitate sea anemones Aiptasia pallida (also known as Exaiptasia diaphana). We, therefore, hypothesize that NANA activates calcium influx via L-type calcium channels. We demonstrate a dose-dependent, NANA-activated 45Ca influx into dissociated ectodermal cells isolated from A. pallida tentacles, with maximal influx occurring at desensitizing concentrations of NANA. The L-type calcium channel inhibitors nifedipine, diltiazem, methoxyverapamil, and cadmium blocked NANA-stimulated 45Ca influx. Elevated extracellular KCl levels dose-dependently increased nifedipine-sensitive 45Ca influx to implicate voltage-gated calcium channels. Forskolin, 8-bromo-cAMP, and the protein kinase A inhibitor H-8 affect NANA-stimulated calcium influx in a manner consistent with activated cAMP-dependent pathway involvement. Because NANA chemoreceptors localize to supporting cells of cnidocyte supporting cell complexes, NANA activation of 45Ca influx into isolated tentacle ectodermal cells suggests that L-type calcium channels and NANA chemoreceptors co-localize to supporting cells. Indeed, a fluorescent marker of L-type calcium channels localizes to the apical ectoderm adjacent to nematocysts of live tentacles. We conclude that supporting cell chemoreceptors activate co-localized L-type calcium channels via a cAMP-dependent mechanism in order to initiate desensitization. We suggest that pathway desensitization may conserve nematocysts from excessive discharge during prey capture.

Temperature-induced alteration of the extracellular matrix in the tropical sea anemone, Exaiptasia pallida

Coral bleaching results from the loss of the endosymbiotic dinoflagellate the cells of coral. The symbionts provide photosynthetic products for nourishment of the coral, and loss of the symbiont can result in death of the coral. Many stressors can cause coral bleaching, but we are focusing on the effect of increased water temperature in this research because of rising oceanic temperatures. We are how investigating how increased temperature affects the extracellular matrix (ECM) using the tropical sea anemone, Exaiptasia pallida as our model organism, since this anemone has similar physiological characteristics and similar symbionts as coral. Research on the effects of a heat-shock (from 25°C to 30°C) in anemones embedded, sectioned, and then stained with the Russel-Movat Pentachrome stain showed that the mesoglea of the anemone, was altered after a 12 hour heat-shock compared to control anemones. To confirm these findings, staining with an additional ECM stain, Masson’s Trichrome, will be conducted. Additionally, we are investigating how alteration in the ECM because of increased temperature affects apoptosis to determine if there is a positive correlation between temperature-induced changes in the ECM and loss of cells through apoptosis. Results from these experiments will help us better understand the timing and consequences of temperature-induced breakdown of the coral-algal symbiosis.

Impact of Menthol on Growth and Photosynthetic Function of Breviolum Minutum (Dinoflagellata, Dinophyceae, Symbiodiniaceae) and Interactions with its Aiptasia Host.

Environmental change, including global warming and chemical pollution, can compromise cnidarian-(e.g., coral-) dinoflagellate symbioses and cause coral bleaching. Understanding the mechanisms that regulate these symbioses will inform strategies for sustaining healthy coral-reef communities. A model system for corals is the symbiosis between the sea anemone Exaiptasia pallida (common name Aiptasia) and its dinoflagellate partners (family Symbiodiniaceae). To complement existing studies of the interactions between these organisms, we examined the impact of menthol, a reagent often used to render cnidarians aposymbiotic, on the dinoflagellate Breviolum minutum, both in culture and in hospite. In both environments, the growth and photosynthesis of this alga were compromised at either 100 or 300µM menthol. We observed reduction in PSII and PSI functions, the abundances of reaction-center proteins, and, at 300µM menthol, of total cellular proteins. Interestingly, for free-living algae exposed to 100µM menthol, an initial decline in growth, photosynthetic activities, pigmentation, and protein abundances reversed after 5-15 d, eventually approaching control levels. This behavior was observed in cells maintained in continuous light, but not in cells experiencing a light-dark regimen, suggesting that B. minutum can detoxify menthol or acclimate and repair damaged photosynthetic complexes in a light- and/or energy-dependent manner. Extended exposures of cultured algae to 300µM menthol ultimately resulted in algal death. Most symbiotic anemones were also unable to survive this menthol concentration for 30 d. Additionally, cells impaired for photosynthesis by pre-treatment with 300µM menthol exhibited reduced efficiency in re-populating the anemone host.

Metabolomic shifts associated with heat stress in coral holobionts.

Understanding the response of the coral holobiont to environmental change is crucial to inform conservation efforts. The most pressing problem is "coral bleaching," usually precipitated by prolonged thermal stress. We used untargeted, polar metabolite profiling to investigate the physiological response of the coral species Montipora capitata and Pocillopora acuta to heat stress. Our goal was to identify diagnostic markers present early in the bleaching response. From the untargeted UHPLC-MS data, a variety of co-regulated dipeptides were found that have the highest differential accumulation in both species. The structures of four dipeptides were determined and showed differential accumulation in symbiotic and aposymbiotic (alga-free) populations of the sea anemone Aiptasia (Exaiptasia pallida), suggesting the deep evolutionary origins of these dipeptides and their involvement in symbiosis. These and other metabolites may be used as diagnostic markers for thermal stress in wild coral.

Manganese Uptake and Partitioning between the Tissue of the Anemone Host Exaiptasia Pallida and Symbiodinium Sp., Including Assessment of Stress and Recovery

Manganese Uptake and Partitioning between the Tissue of the Anemone Host Exaiptasia Pallida and Symbiodinium Sp., Including Assessment of Stress and Recovery

Gene expression kinetics of Exaiptasia pallida innate immune response to Vibrio parahaemolyticus infection

Recent sequencing projects on early-diverging metazoans such as cnidarians, have unveiled a rich innate immunity gene repertoire; however, little is known about immunity gene regulation in the host’s early response against marine bacterial pathogens over time. Here, we used RNA-seq on the sea anemone Exaiptasia pallida (Ep) strain CC7 as a model to depict the innate immune response during the onset of infection with the marine pathogenic bacteria Vibrio parahaemolyticus (Vp) clinical strain O3:K6, and lipopolysaccharides (LPS) exposure. Pairwise and time series analyses identified the genes responsive to infection as well as the kinetics of innate immune genes over time. Comparisons between the responses to live Vp and purified LPS was then performed. Gene expression and functional analyses detected hundreds to thousands of genes responsive to the Vp infection after 1, 3, 6 and 12 h, including a few shared with the response to LPS. Our results bring to light the first indications that non-canonical cytoplasmic pattern recognition receptors (PRRs) such as NOD-like and RIG-I-like receptor homologs take part in the immune response of Ep. Over-expression of several members of the lectin-complement pathways in parallel with novel transmembrane and Ig containing ficolins (CniFLs) suggest an active defense against the pathogen. Although lacking typical Toll-like receptors (TLRs), Ep activates a TLR-like pathway including the up-regulation of MyD88, TRAF6, NF-κB and AP-1 genes, which are not induced under LPS treatment and therefore suggest an alternative ligand-to-PRR trigger. Two cytokine-dependent pathways involving Tumor necrosis factor receptors (TNFRs) and several other potential downstream signaling genes likely lead to inflammation and/or apoptosis. Finally, both the extrinsic and intrinsic apoptotic pathways were strongly supported by over-expression of effector and executioner genes. To our knowledge, this pioneering study is first to follow the kinetics of the innate immune response in a cnidarian during the onset of infection with a bacterial pathogen. Overall, our findings reveal the involvement of both novel immune gene candidates such as NLRs, RLRs and CniFLs, and previously identified TLR-like and apoptotic pathways in anthozoan innate immunity with a large amount of transcript-level evidence.

Gene expression kinetics of Exaiptasia pallida innate immune response to Vibrio parahaemolyticus infection

BackgroundRecent sequencing projects on early-diverging metazoans such as cnidarians, have unveiled a rich innate immunity gene repertoire; however, little is known about immunity gene regulation in the host’s early response against marine bacterial pathogens over time. Here, we used RNA-seq on the sea anemone Exaiptasia pallida (Ep) strain CC7 as a model to depict the innate immune response during the onset of infection with the marine pathogenic bacteria Vibrio parahaemolyticus (Vp) clinical strain O3:K6, and lipopolysaccharides (LPS) exposure. Pairwise and time series analyses identified the genes responsive to infection as well as the kinetics of innate immune genes over time. Comparisons between the responses to live Vp and purified LPS was then performed.ResultsGene expression and functional analyses detected hundreds to thousands of genes responsive to the Vp infection after 1, 3, 6 and 12 h, including a few shared with the response to LPS. Our results bring to light the first indications that non-canonical cytoplasmic pattern recognition receptors (PRRs) such as NOD-like and RIG-I-like receptor homologs take part in the immune response of Ep. Over-expression of several members of the lectin-complement pathways in parallel with novel transmembrane and Ig containing ficolins (CniFLs) suggest an active defense against the pathogen. Although lacking typical Toll-like receptors (TLRs), Ep activates a TLR-like pathway including the up-regulation of MyD88, TRAF6, NF-κB and AP-1 genes, which are not induced under LPS treatment and therefore suggest an alternative ligand-to-PRR trigger. Two cytokine-dependent pathways involving Tumor necrosis factor receptors (TNFRs) and several other potential downstream signaling genes likely lead to inflammation and/or apoptosis. Finally, both the extrinsic and intrinsic apoptotic pathways were strongly supported by over-expression of effector and executioner genes.ConclusionsTo our knowledge, this pioneering study is first to follow the kinetics of the innate immune response in a cnidarian during the onset of infection with a bacterial pathogen. Overall, our findings reveal the involvement of both novel immune gene candidates such as NLRs, RLRs and CniFLs, and previously identified TLR-like and apoptotic pathways in anthozoan innate immunity with a large amount of transcript-level evidence.

A shift away from mutualism under food-deprived conditions in an anemone-dinoflagellate association.

The mutualistic symbiosis between anthozoans and intra-gastrodermal dinoflagellates of the family Symbiodiniaceae is the functional basis of all coral reef ecosystems, with the latter providing up to 95% of their fixed photosynthate to their hosts in exchange for nutrients. However, recent studies of sponges, jellyfish, and anemones have revealed the potential for this mutualistic relationship to shift to parasitism under stressful conditions. Over a period of eight weeks, we compared the physiological conditions of both inoculated and aposymbiotic anemones (Exaiptasia pallida) that were either fed or starved. By the sixth week, both fed groups of anemones were significantly larger than their starved counterparts. Moreover, inoculated and starved anemones tended to disintegrate into “tissue balls” within eight weeks, and 25% of the samples died; in contrast, starved aposymbiotic anemones required six months to form tissue balls, and no anemones from this group died. Our results show that the dinoflagellates within inoculated anemones may have posed a fatal metabolic burden on their hosts during starvation; this may be because of the need to prioritize their own metabolism and nourishment at the expense of their hosts. Collectively, our study reveals the potential of this dynamic symbiotic association to shift away from mutualism during food-deprived conditions.