Characterization of trade-offs between immunity and reproduction in the coral species Astrangia poculata

Background

Living organisms face ubiquitous pathogenic threats and have consequently evolved immune systems to protect against potential invaders. However, many components of the immune system are physiologically costly to maintain and engage, often drawing resources away from other organismal processes such as growth and reproduction. Evidence from a diversity of systems has demonstrated that organisms use complex resource allocation mechanisms to manage competing needs and optimize fitness. However, understanding of resource allocation patterns is limited across taxa. Cnidarians, which include ecologically important organisms like hard corals, have been historically understudied in the context of resource allocations. Improving understanding of resource allocation-associated trade-offs in cnidarians is critical for understanding future ecological dynamics in the face of rapid environmental change.

Methods

Here, we characterize trade-offs between constitutive immunity and reproduction in the facultatively symbiotic coral Astrangia poculata. Male colonies underwent ex situ spawning and sperm density was quantified. We then examined the effects of variable symbiont density and energetic budget on physiological traits, including immune activity and reproductive investment. Furthermore, we tested for potential trade-offs between immune activity and reproductive investment.

Results

We found limited associations between energetic budget and immune metrics; melanin production was significantly positively associated with carbohydrate concentration. However, we failed to document any associations between immunity and reproductive output which would be indicative of trade-offs, possibly due to experimental limitations. Our results provide a preliminary framework for future studies investigating immune trade-offs in cnidarians.

Bioprospecting of Sea Anemones (Cnidaria, Anthozoa, Actiniaria) for β-Defensin-like α-Amylase Inhibitors

Diabetes mellitus is one of the most serious diseases of our century. The drugs used are limited or have serious side effects. The search for new sources of compounds for effective treatment is relevant. Magnificamide, a peptide inhibitor of mammalian α-amylases, isolated from the venom of sea anemone Heteractis magnifica, can be used for the control of postprandial hyperglycemia in diabetes mellitus. Using the RACE approach, seven isoforms of magnificamide were detected in H. magnifica tentacles. The exon-intron structure of magnificamide genes was first established, and intron retention in the mature peptide-encoding region was revealed. Additionally, an α-amylase inhibitory domain was discovered in the mucins of some sea anemones. According to phylogenetics, sea anemones diverge into two groups depending on the presence of β-defensin-like α-amylase inhibitors and/or mucin-inhibitory domains. It is assumed that the intron retention phenomenon leads to additional diversity in the isoforms of inhibitors and allows for its neofunctionalization in sea anemone tentacles. Bioprospecting of sea anemones of the order Actiniaria for β-defensin-like α-amylase inhibitors revealed a diversity of inhibitory sequences that represents a starting point for the design of effective glucose-lowering drugs.

Cnidofest 2022: hot topics in cnidarian research

The second annual Cnidarian Model Systems Meeting, aka "Cnidofest", took place in Davis, California from 7 to 10th of September, 2022. The meeting brought together scientists using cnidarians to study molecular and cellular biology, development and regeneration, evo-devo, neurobiology, symbiosis, physiology, and comparative genomics. The diversity of topics and species represented in presentations highlighted the importance and versatility of cnidarians in addressing a wide variety of biological questions. In keeping with the spirit of the first meeting (and its predecessor, Hydroidfest), almost 75% of oral presentations were given by early career researchers (i.e., graduate students and postdocs). In this review, we present research highlights from the meeting.

Emerging models: The "development" of the ctenophore Mnemiopsis leidyi and the cnidarian Nematostella vectensis as useful experimental models

The goal of this chapter is to explain the reasoning for developing two understudied invertebrate animal species for asking specific biological questions. The first is the ctenophore (comb jelly) Mnemiopsis leidyi and the second is the anthozoan cnidarian (starlet sea anemone) Nematostella vectensis. Although these two taxa belong to some of the earliest branching extant metazoan clades, their developmental features could hardly be more different from one another. This should serve as a general warning to be careful when extrapolating comparisons of one species to another. Two-taxon comparisons are especially flawed; and to interpret features in a phylogenetic context one must sample carefully within a given taxon to determine how representative certain features are before comparing with other clades. The other benefit of this comparison is to identify key practical factors when attempting to develop new species for experimental investigation.

Cnidarians as a potential source of antiparasitic drugs

New antiparasitic drugs are urgently required for treating parasitic infections. The marine environment has proven to be a valuable source of compounds with therapeutic properties against many diseases, including parasitic diseases. Cnidarian venoms are known for their toxicological properties and are candidates for developing medications. In this review, the antiparasitic properties of cnidarian toxins, discovered over the last two decades, were examined. A total of 61 cnidarian compounds from 18 different genera of cnidaria were studied for their antiparasitic activities. The assessed genera belonged mainly to three geographical areas: South America, North America, and Southeast Asia. The in vitro activities of crude extracts and compounds against a range of parasites including Plasmodium falciparum, Trypanosoma brucei gambiense, T. cruzi, T. congolense, Leishmania donovani, L. chagasi, L. braziliensis, and Giardia duodenalis are reviewed. The challenges involved in developing these compounds into effective drugs are discussed.

Molecular and skeletal fingerprints of scleractinian coral biomineralization: From the sea surface to mesophotic depths

Reef-building corals, the major producers of biogenic calcium carbonate, form skeletons in a plethora of morphological forms. Here we studied skeletal modifications of Stylophora pistillata (clade 4) colonies that adapt to increasing depths with decreasing ambient light. The coral show characteristic transitions from spherical morphologies (shallow depths, 5 m deep) to flat and branching geometries (mesophotic depths, 60 m deep). Such changes are typically ascribed to the algal photosymbiont physiological feedback with the coral that host them. We find specific fine-scale skeletal variability in accretion of structure at shallow- and mesophotic depth morphotypes that suggest underlying genomic regulation of biomineralization pathways of the coral host. To explain this, we conducted comparative morphology-based analyses, including optical and electron microscopy, tomography and X-ray diffraction analysis coupled with a comprehensive transcriptomic analysis of S. pistillata. The samples originated from Gulf of Eilat in the Red Sea collected along a depth gradient from shallow to mesophotic depths (5 to 60 m). Additional samples were experimentally transplanted from 5 m to 60 m and from 60 m to 5 m. Interestingly, both morphologically and functionally, transplanted corals partly adapt by exhibiting typical depth-specific properties. In mesophotic depths, we find that the organic matrix fraction is enriched in the coralla, well matching the overrepresentation of transcripts encoding biomineralization "tool-kit" structural extracellularproteins that was observed. These results provide insights into the molecular mechanisms of calcification and skeletal adaptation that repeatedly allowed this coral group to adapt to a range of environments presumably with a rich geological past. STATEMENT OF SIGNIFICANCE: Understanding the reef coral physiological plasticity under a rapidly changing climate is of crucial importance for the protection of coral reef ecosystems. Most of the reef corals operate near their upper limit of heat tolerance. A possible rescue for some coral species is migration to deeper, cooler mesophotic depths. However, gradually changing environmental parameters (especially light) along the depth gradient pose new adaptative stress on corals with largely unknown influences on the various biological molecular pathways. This work provides a first comprehensive analysis of changes in gene expression, including biomineralization "tool kit" genes, and reports the fine-scale microstructural and crystallographic skeletal details in S. pistillata collected in the Red Sea along a depth gradient spannign 5 to 60 m.

Investigating the roles of transforming growth factor-beta in immune response of Orbicella faveolata, a scleractinian coral

Symbiotic relationships range from parasitic to mutualistic, yet all endosymbionts face similar challenges, including evasion of host immunity. Many symbiotic organisms have evolved similar mechanisms to face these challenges, including manipulation of the host's transforming growth factor-beta (TGFβ) pathway. Here we investigate the TGFβ pathway in scelaractinian corals which are dependent on symbioses with dinoflagellates from the family Symbiodiniaceae. Using the Caribbean coral, Orbicella faveolata, we explore the effects of enhancement and inhibition of the TGFβ pathway on host gene expression. Following transcriptomic analyses, we demonstrated limited effects of pathway manipulation in absence of immune stimulation. However, manipulation of the TGFβ pathway significantly affects the subsequent ability of host corals to mount an immune response. Enhancement of the TGFβ pathway eliminates transcriptomic signatures of host coral immune response, while inhibition of the pathway maintains the response. This is, to our knowledge, the first evidence of an immunomodulatory role for TGFβ in a scelaractinian coral. These findings suggest variation in TGFβ signaling may have implications in the face of increasing disease prevelance. Our results suggest that the TGFβ pathway can modulate tradeoffs between symbiosis and immunity. Further study of links between symbiosis, TGFβ, and immunity is needed to better understand the ecological implications of these findings.

Cnidofest 2018: the future is bright for cnidarian research

The 2018 Cnidarian Model Systems Meeting (Cnidofest) was held September 6-9th at the University of Florida Whitney Laboratory for Marine Bioscience in St. Augustine, FL. Cnidofest 2018, which built upon the momentum of Hydroidfest 2016, brought together research communities working on a broad spectrum of cnidarian organisms from North America and around the world. Meeting talks covered diverse aspects of cnidarian biology, with sessions focused on genomics, development, neurobiology, immunology, symbiosis, ecology, and evolution. In addition to interesting biology, Cnidofest also emphasized the advancement of modern research techniques. Invited technology speakers showcased the power of microfluidics and single-cell transcriptomics and demonstrated their application in cnidarian models. In this report, we provide an overview of the exciting research that was presented at the meeting and discuss opportunities for future research.

Global Shifts in Gene Expression Profiles Accompanied with Environmental Changes in Cnidarian-Dinoflagellate Endosymbiosis

Stable endosymbiotic relationships between cnidarian animals and dinoflagellate algae are vital for sustaining coral reef ecosystems. Recent studies have shown that elevated seawater temperatures can cause the collapse of their endosymbiosis, known as 'bleaching', and result in mass mortality. However, the molecular interplay between temperature responses and symbiotic states still remains unclear. To identify candidate genes relevant to the symbiotic stability, we performed transcriptomic analyses under multiple conditions using the symbiotic and apo-symbiotic (symbiont free) Exaiptasia diaphana, an emerging model sea anemone. Gene expression patterns showed that large parts of differentially expressed genes in response to heat stress were specific to the symbiotic state, suggesting that the host sea anemone could react to environmental changes in a symbiotic state-dependent manner. Comparative analysis of expression profiles under multiple conditions highlighted candidate genes potentially important in the symbiotic state transition under heat-induced bleaching. Many of these genes were functionally associated with carbohydrate and protein metabolisms in lysosomes. Symbiont algal genes differentially expressed in hospite encode proteins related to heat shock response, calcium signaling, organellar protein transport, and sugar metabolism. Our data suggest that heat stress alters gene expression in both the hosts and symbionts. In particular, heat stress may affect the lysosome-mediated degradation and transportation of substrates such as carbohydrates through the symbiosome (phagosome-derived organelle harboring symbiont) membrane, which potentially might attenuate the stability of symbiosis and lead to bleaching-associated symbiotic state transition.

Hydra vulgaris exhibits day-night variation in behavior and gene expression levels

BACKGROUND

Day-night behavioral variation is observed in most organisms, and is generally controlled by circadian clocks and/or synchronization to environmental cues. Hydra species, which are freshwater cnidarians, are thought to lack the core clock genes that form transcription-translation feedback loops in clock systems. In this study, we examined whether hydras exhibit diel rhythms in terms of behavior and gene expression levels without typical clock genes.

RESULTS

We found that the total behavior of hydras was elevated during the day and decreased at night under a 12-h light-dark cycle. Polyp contraction frequency, one component of behavior, exhibited a clear diel rhythm. However, neither total behavior nor polyp contraction frequency showed rhythmic changes under constant light and constant dark conditions. To identify the genes underlying diel behavior, we performed genome-wide transcriptome analysis of hydras under light-dark cycles. Using three different analytic algorithms, we found that 380 genes showed robust diel oscillations in expression. Some of these genes shared common features with diel cycle genes of other cnidarian species with endogenous clock systems.

CONCLUSION

Hydras show diel behavioral rhythms under light-dark cycles despite the absence of canonical core clock genes. Given the functions of the genes showing diel oscillations in hydras and the similarities of those genes with the diel cycle genes of other cnidarian species with circadian clocks, it is possible that diel cycle genes play an important role across cnidarian species regardless of the presence or absence of core clock genes under light-dark cycles.

Natural Compounds and Drug Discovery: Can Cnidarian Venom Play a Role?

Natural compounds extracted from organisms and microorganisms are an important resource for the development of drugs and bioactive molecules. Many such compounds have made valuable contributions in diverse fields such as human health, pharmaceutics and industrial applications. Presently, however, research on investigating natural compounds from marine organisms is scarce. This is somewhat surprising considering that the marine environment makes a major contribution to Earth's ecosystems and consequently possesses a vast storehouse of diverse marine species. Interestingly, of the marine bioactive natural compounds identified to date, many are venoms, coming from Cnidarians (jellyfish, sea anemones, corals). Cnidarians are therefore particularly interesting marine species, producing important biological compounds that warrant further investigation for their development as possible therapeutic agents. From an experimental aspect, this review aims to emphasize and update the current scientific knowledge reported on selected biological activity (antiinflammatory, antimicrobial, antitumoral, anticoagulant, along with several less studied effects) of Cnidarian venoms/extracts, highlighting potential aspects for ongoing research towards their utilization in human therapeutic approaches.

Fatal Pulmonary Edema in a Child After Jellyfish Stings in Korea

Jellyfish have been increasing at a global scale in recent years. These blooms not only have deleterious effects on marine ecosystems, they also increase the risk of jellyfish stings and accompanying envenomation. Here, we report a fatal case of pulmonary edema caused by jellyfish envenomation in a child in Korea. The patient died 4 h after envenomation despite cardiopulmonary resuscitation. Nemopilema nomurai was the suspected species of jellyfish encountered by the patient, although we are unable to confirm this. With this case report, we aim to inform on the serious issue of toxicity associated with jellyfish species that bloom mainly along Korean, east Chinese, and Japanese shores and to discuss appropriate first aid methods in case of jellyfish stings.

The cell specificity of gene expression in the response to heat stress in corals

Previous transcriptional studies in heat-stressed corals have shown that many genes are responsive to generalized heat stress whereas the expression patterns of specific gene networks after heat stress show strong correlations with variation in bleaching outcomes. However, where these specific genes are expressed is unknown. In this study, we employed in situ hybridization to identify patterns of spatial gene expression of genes previously predicted to be involved in general stress response and bleaching. We found that tumor necrosis factor receptors (TNFRs), known to be strong responders to heat stress, were not expressed in gastrodermal symbiont-containing cells but were widely expressed in specific cells of the epidermal layer. The transcription factors AP-1 and FosB, implicated as early signals of heat stress, were widely expressed throughout the oral gastrodermis and epidermis. By contrast, a G protein-coupled receptor gene (GPCR) and a fructose bisphosphate aldolase C gene (aldolase), previously implicated in bleaching, were expressed in symbiont-containing gastrodermal cells and in the epidermal tissue. Finally, chordin-like/kielin (chordin-like), a gene highly correlated to bleaching, was expressed solely in the oral gastrodermis. From this study, we confirm that heat-responsive genes occur widely in coral tissues outside of symbiont-containing cells. Joint information about expression patterns in response to heat and cell specificity will allow greater dissection of the regulatory pathways and specific cell reactions that lead to coral bleaching.

Structure and signaling at hydroid polyp-stolon junctions, revisited

The gastrovascular system of colonial hydroids is central to homeostasis, yet its functional biology remains poorly understood. A probe (2′,7′-dichlorodihydrofluorescein diacetate) for reactive oxygen species (ROS) identified fluorescent objects at polyp-stolon junctions that emit high levels of ROS. A nuclear probe (Hoechst 33342) does not co-localize with these objects, while a mitochondrial probe (rhodamine 123) does. We interpret these objects as mitochondrion-rich cells. Confocal microscopy showed that this fluorescence is situated in large columnar cells. Treatment with an uncoupler (2,4-dinitrophenol) diminished the ROS levels of these cells relative to background fluorescence, as did removing the stolons connecting to a polyp-stolon junction. These observations support the hypothesis that the ROS emanate from mitochondrion-rich cells, which function by pulling open a valve at the base of the polyp. The open valve allows gastrovascular fluid from the polyp to enter the stolons and vice versa. The uncoupler shifts the mitochondrial redox state in the direction of oxidation, lowering ROS levels. By removing the stolons, the valve is not pulled open, metabolic demand is lowered, and the mitochondrion-rich cells slowly regress. Transmission electron microscopy identified mitochondrion-rich cells adjacent to a thick layer of mesoglea at polyp-stolon junctions. The myonemes of these myoepithelial cells extend from the thickened mesoglea to the rigid perisarc on the outside of the colony. The perisarc thus anchors the myoepithelial cells and allows them to pull against the mesoglea and open the lumen of the polyp-stolon junction, while relaxation of these cells closes the lumen.

Unravelling the role of zooxanthellae in the uptake and depuration of an essential metal in Exaiptasia pallida; an experiment using a model cnidarian

Coral skeletons record historical trace metal levels in the environment, however, the use of coral skeletal records for biomonitoring studies mostly fail to consider the influence of metal regulation by the living components of coral and subsequent incorporation into the skeleton. This study presents Exaiptasia pallida as a representative of the living components of coral and shows metal partitioning between the tissue and zooxanthellae after chronic exposure to Zn. A strong tendency for preferential accumulation in the zooxanthellae occurred after 32 days exposure and Zn concentrations in tissue and zooxanthellae were 123.3±0.7 mg kg(-1) and 294.9±8.5 respectively. This study shows zooxanthellae density plays an important role in controlling Zn loading in whole anemones and must be considered when investigating metal uptake and loading in zooxanthellate organisms. Further studies that investigate links between aragonite deposition rates and zooxanthellae density and incorporation pathways of metals into skeleton are warranted.

Internal carbonic anhydrase activity in the tissue of scleractinian corals is sufficient to support proposed roles in photosynthesis and calcification

Reef-building corals import inorganic carbon (Ci) to build their calcium carbonate skeletons and to support photosynthesis by the symbiotic algae that reside in their tissue. The internal pathways that deliver Ci for both photosynthesis and calcification are known to involve the enzyme carbonic anhydrase (CA), which interconverts CO2 and HCO3 (-). We have developed a method for absolute quantification of internal CA (iCA) activity in coral tissue based on the rate of (18)O-removal from labeled Ci. The method was applied to three Caribbean corals (Orbicella faveolata, Porites astreoides and Siderastrea radians) and showed that these species have similar iCA activities per unit surface area, but that S. radians has ∼10-fold higher iCA activity per unit tissue volume. A model of coral Ci processing shows that the measured iCA activity is sufficient to support the proposed roles for iCA in Ci transport for photosynthesis and calcification. This is the case even when iCA activity is homogeneously distributed throughout the coral, but the model indicates that it would be advantageous to concentrate iCA in the spaces where calcification (the calcifying fluid) and photosynthesis (the oral endoderm) take place. We argue that because the rates of photosynthesis and calcification per unit surface area are similar among the corals studied here, the areal iCA activity used to deliver Ci for these reactions should also be similar. The elevated iCA activity per unit volume of S. radians compared with that of the other species is probably due to the thinner effective tissue thickness in this species.

Evolution of TNF-induced apoptosis reveals 550 My of functional conservation

The Precambrian explosion led to the rapid appearance of most major animal phyla alive today. It has been argued that the complexity of life has steadily increased since that event. Here we challenge this hypothesis through the characterization of apoptosis in reef-building corals, representatives of some of the earliest animals. Bioinformatic analysis reveals that all of the major components of the death receptor pathway are present in coral with high-predicted structural conservation with Homo sapiens. The TNF receptor-ligand superfamilies (TNFRSF/TNFSF) are central mediators of the death receptor pathway, and the predicted proteome of Acropora digitifera contains more putative coral TNFRSF members than any organism described thus far, including humans. This high abundance of TNFRSF members, as well as the predicted structural conservation of other death receptor signaling proteins, led us to wonder what would happen if corals were exposed to a member of the human TNFSF (HuTNFα). HuTNFα was found to bind directly to coral cells, increase caspase activity, cause apoptotic blebbing and cell death, and finally induce coral bleaching. Next, immortalized human T cells (Jurkats) expressing a functional death receptor pathway (WT) and a corresponding Fas-associated death domain protein (FADD) KO cell line were exposed to a coral TNFSF member (AdTNF1) identified and purified here. AdTNF1 treatment resulted in significantly higher cell death (P < 0.0001) in WT Jurkats compared with the corresponding FADD KO, demonstrating that coral AdTNF1 activates the H. sapiens death receptor pathway. Taken together, these data show remarkable conservation of the TNF-induced apoptotic response representing 550 My of functional conservation.