Aggregation of sea urchin phagocytes is augmented in vitro by lipopolysaccharide

Treatment of Acute Liver Injury through Selective Tropism of High Mobility Group Box 1 Gene-Silenced Large Peritoneal Macrophages

Tissue-resident macrophages (TRMs) are attractive cells to therapeutically deliver oligonucleotide and other gene-expression modifying modalities to treat a wide array of diseases ranging from inflammatory to autoimmune, and even cancer. Here, we focus on TRMs located inside the peritoneal cavity lining the abdomen that selectively express a transcription factor GATA6 called large peritoneal macrophages (GLPMs) and successfully demonstrate functional GLPM-selective delivery of a Cy5-fluorophore-labeled siRNA encapsulated in C12-200 cationic-lipidoid-based nanoparticles (siRNA-Cy5 (C12-200)). Despite being TRMs, GLPMs possess a specific migratory ability to peritoneally located liver tissue upon injury incited by acetaminophen (APAP) overdose in mice. A rapid, liver injury-driven tropism of GLPMs carrying siRNA-Cy5 (C12-200) was seen via systemic circulation, which was elegantly demonstrated by using a noninvasive live-cell tracking technique called diffuse in vivo flow cytometry (DiFC). Finally, RNAi-mediated silencing of a well-known pro-inflammatory damage-associated molecular pattern (DAMP) High Mobility Group Box-1 (HMGB1) gene in GLPMs led to the mitigation of liver injury and inflammation via prevention of GLPM modulation to a pro-inflammatory state, which further translated into significant protection from APAP-driven liver injury and a reduction in liver circulating pro-inflammatory cytokines owing to a muted inflammatory response to acute liver injury. Moreover, silencing HMGB1 by a GalNAc-conjugated hepatocyte-targeting siRNA did not reciprocate the findings, further solidifying our results. Together, our data suggested that GLPMs act as delivery carriers by rapidly bringing lipid nanoparticle-encapsulated RNAi modalities to the injured liver and have emerged as a therapeutically viable strategy to address inflammatory diseases, especially those that are more acute in nature.

Recombinant SpTransformer proteins are functionally diverse for binding and phagocytosis by three subtypes of sea urchin phagocytes

Introduction

The California purple sea urchin, Strongylocentrotus purpuratus, relies solely on an innate immune system to combat the many pathogens in the marine environment. One aspect of their molecular defenses is the SpTransformer (SpTrf) gene family that is upregulated in response to immune challenge. The gene sequences are highly variable both within and among animals and likely encode thousands of SpTrf isoforms within the sea urchin population. The native SpTrf proteins bind foreign targets and augment phagocytosis of a marine Vibrio. A recombinant (r)SpTrf-E1-Ec protein produced by E. coli also binds Vibrio but does not augment phagocytosis.

Methods

To address the question of whether other rSpTrf isoforms function as opsonins and augment phagocytosis, six rSpTrf proteins were expressed in insect cells.

Results

The rSpTrf proteins are larger than expected, are glycosylated, and one dimerized irreversibly. Each rSpTrf protein cross-linked to inert magnetic beads (rSpTrf::beads) results in different levels of surface binding and phagocytosis by phagocytes. Initial analysis shows that significantly more rSpTrf::beads associate with cells compared to control BSA::beads. Binding specificity was verified by pre-incubating the rSpTrf::beads with antibodies, which reduces the association with phagocytes. The different rSpTrf::beads show significant differences for cell surface binding and phagocytosis by phagocytes. Furthermore, there are differences among the three distinct types of phagocytes that show specific vs. constitutive binding and phagocytosis.

Conclusion

These findings illustrate the complexity and effectiveness of the sea urchin innate immune system driven by the natSpTrf proteins and the phagocyte cell populations that act to neutralize a wide range of foreign pathogens.

Scoping intergenerational effects of nanoplastic on the lipid reserves of Antarctic krill embryos

Antarctic krill (Euphausia superba) plays a central role in the Antarctic marine food web and biogeochemical cycles and has been identified as a species that is potentially vulnerable to plastic pollution. While plastic pollution has been acknowledged as a potential threat to Southern Ocean marine ecosystems, the effect of nanoplastics (<1000 nm) is poorly understood. Deleterious impacts of nanoplastic are predicted to be higher than that of larger plastics, due to their small size which enables their permeation of cell membranes and potentially provokes toxicity. Here, we investigated the intergenerational impact of exposing Antarctic krill to nanoplastics. We focused on whether embryonic energy resources were affected when gravid female krill were exposed to nanoplastic by determining lipid and fatty acid compositions of embryos produced in incubation. Embryos were collected from females who had spawned under three different exposure treatments (control, nanoplastic, nanoplastic + algae). Embryos collected from each maternal treatment were incubated for a further 6 days under three nanoplastic exposure treatments (control, low concentration nanoplastic, and high concentration nanoplastic). Nanoplastic additions to seawater did not impact lipid metabolism (total lipid or fatty acid composition) across the maternal or direct embryo treatments, and no interactive effects were observed. The provision of a food source during maternal exposure to nanoplastic had a positive effect on key fatty acids identified as important during embryogenesis, including higher total polyunsaturated fatty acids (PUFA), eicosapentaenoic acid (EPA) and docosahexaenoic acid (DHA) when compared to the control and nanoplastic treatments. Whilst the short exposure time was ample for lipids from maternally digested algae to be incorporated into embryos, we discuss why the nanoplastic-fatty acid relationship may be more complex. Our study is the first to scope intergeneration effects of nanoplastic on Antarctic krill lipid and fatty acid reserves. From this, we suggest directions for future research including long term exposures, multi-stressor scenarios and exploring other critical energy reserves such as proteins.

Gata6+ large peritoneal macrophages: an evolutionarily conserved sentinel and effector system for infection and injury

There are striking similarities between the sea urchin cavity macrophage-like phagocytes (coelomocytes) and mammalian cavity macrophages in not only their location, but also their behaviors. These cells are crucial for maintaining homeostasis within the cavity following a breach, filling the gap and functioning as a barrier between vital organs and the environment. In this review, we summarize the evolving literature regarding these Gata6⁺ large peritoneal macrophages (GLPMs), focusing on ontogeny, their responses to perturbations, including their rapid aggregation via coagulation, as well as scavenger receptor cysteine-rich domains and their potential roles in diseases, such as cancer. We challenge the 50-year old phenomenon of the 'macrophage disappearance reaction' (MDR) and propose the new term 'macrophage disturbance of homeostasis reaction' (MDHR), which may better describe this complex phenomenon.

Establishment of the immunological self in juvenile Patiria pectinifera post-metamorphosis

Ontogeny of the immune system is a fundamental immunology issue. One indicator of immune system maturation is the establishment of the immunological self, which describes the ability of the immune system to distinguish allogeneic individuals (allorecognition ability). However, the timing of immune system maturation during invertebrate ontogeny is poorly understood. In the sea star Patiria pectinifera, cells that have dissociated from the embryos and larvae are able to reconstruct larvae. This reconstruction phenomenon is possible because of a lack of allorecognition capability in the larval immune system, which facilitates the formation of an allogeneic chimera. In this study, we revealed that the adult immune cells of P. pectinifera (coelomocytes) have allorecognition ability. Based on a hypothesis that allorecognition ability is acquired before and after metamorphosis, we conducted detailed morphological observations and survival time analysis of metamorphosis-induced chimeric larvae. The results showed that all allogeneic chimeras died within approximately two weeks to one month of reaching the juvenile stage. In these chimeras, the majority of the epidermal cell layer was lost and the mesenchymal region expanded, but cell death appeared enhanced in the digestive tract. These results indicate that the immunological self of P. pectinifera is established post-metamorphosis during the juvenile stage. This is the first study to identify the timing of immune system maturation during echinodermal ontogenesis. As well as establishing P. pectinifera as an excellent model for studies on self- and non-self-recognition, this study enhances our understanding of the ontogeny of the immune system in invertebrates.

Coelomocyte populations in the sea urchin, Strongylocentrotus purpuratus, undergo dynamic changes in response to immune challenge

The sea urchin, Strongylocentrotus purpuratus has seven described populations of distinct coelomocytes in the coelomic fluid that are defined by morphology, size, and for some types, by known functions. Of these subtypes, the large phagocytes are thought to be key to the sea urchin cellular innate immune response. The concentration of total coelomocytes in the coelomic fluid increases in response to pathogen challenge. However, there is no quantitative analysis of how the respective coelomocyte populations change over time in response to immune challenge. Accordingly, coelomocytes collected from immunoquiescent, healthy sea urchins were evaluated by flow cytometry for responses to injury and to challenge with either heat-killed Vibrio diazotrophicus, zymosan A, or artificial coelomic fluid, which served as the vehicle control. Responses to the initial injury of coelomic fluid collection or to injection of V. diazotrophicus show significant increases in the concentration of large phagocytes, small phagocytes, and red spherule cells after one day. Responses to zymosan A show decreases in the concentration of large phagocytes and increases in the concentration of small phagocytes. In contrast, responses to injections of vehicle result in decreased concentration of large phagocytes. When these changes in coelomocytes are evaluated based on proportions rather than concentration, the respective coelomocyte proportions are generally maintained in response to injection with V. diazotrophicus and vehicle. However, this is not observed in response to zymosan A and this lack of correspondence between proportions and concentrations may be an outcome of clearing these large particles by the large phagocytes. Variations in coelomocyte populations are also noted for individual sea urchins evaluated at different times for their responses to immune challenge compared to the vehicle. Together, these results demonstrate that the cell populations in sea urchin immune cell populations undergo dynamic changes in vivo in response to distinct immune stimuli and to injury and that these changes are driven by the responses of the large phagocyte populations.

A Review of Asteroid Biology in the Context of Sea Star Wasting: Possible Causes and Consequences

AbstractSea star wasting-marked in a variety of sea star species as varying degrees of skin lesions followed by disintegration-recently caused one of the largest marine die-offs ever recorded on the west coast of North America, killing billions of sea stars. Despite the important ramifications this mortality had for coastal benthic ecosystems, such as increased abundance of prey, little is known about the causes of the disease or the mechanisms of its progression. Although there have been studies indicating a range of causal mechanisms, including viruses and environmental effects, the broad spatial and depth range of affected populations leaves many questions remaining about either infectious or non-infectious mechanisms. Wasting appears to start with degradation of mutable connective tissue in the body wall, leading to disintegration of the epidermis. Here, we briefly review basic sea star biology in the context of sea star wasting and present our current knowledge and hypotheses related to the symptoms, the microbiome, the viruses, and the associated environmental stressors. We also highlight throughout the article knowledge gaps and the data needed to better understand sea star wasting mechanistically, its causes, and potential management.

Lipofection mediated transfection fails for sea urchin coelomocytes

Molecular cloning, gene manipulation, gene expression, protein function, and gene regulation all depend on the introduction of nucleic acids into target cells. Multiple methods have been developed to facilitate such delivery including instrument based microinjection and electroporation, biological methods such as transduction, and chemical methods such as calcium phosphate precipitation, cationic polymers, and lipid based transfection, also known as lipofection. Here we report attempts to lipofect sea urchin coelomocytes using DOTAP lipofection reagent packaged with a range of molecules including fluorochromes, in addition to expression constructs, amplicons, and RNA encoding GFP. DOTAP has low cytotoxicity for coelomocytes, however, lipofection of a variety of molecules fails to produce any signature of success based on results from fluorescence microscopy and flow cytometry. While these results are negative, it is important to report failed attempts so that others conducting similar research do not repeat these approaches. Failure may be the outcome of elevated ionic strength of the coelomocyte culture medium, uptake and degradation of lipoplexes in the endosomal-lysosomal system, failure of the nucleic acids to escape the endosomal vesicles and enter the cytoplasm, and difficulties in lipofecting primary cultures of phagocytic cells. We encourage others to build on this report by using our information to optimize lipofection with a range of other approaches to work towards establishing a successful method of transfecting adult cells from marine invertebrates.

A flow cytometry based approach to identify distinct coelomocyte subsets of the purple sea urchin, Strongylocentrotus purpuratus

The sea urchin, Strongylocentrotus purpuratus, possesses at least seven distinguishable cell populations in the coelomic fluid, which vary in morphology, size, and function. Of these, the large phagocytes, small phagocytes, and red spherule cells are thought to be key to the echinoid immune response. Because there are currently no effective and rapid means of evaluating sea urchin coelomocytes, we developed a flow cytometry based approach to identify these subsets from unseparated, unstained, live cells. In particular our gating strategy distinguishes between the large phagocytes, small phagocytes, red spherule cells, and a mixed population of vibratile cells and colorless spherule cells. This flow cytometry based analysis increases the speed and improves the reliability of coelomocyte analysis compared to differential cell counts by microscopy.

Rainbow bodies: Revisiting the diversity of coelomocyte aggregates and their synthesis in echinoderms

The innate immunity of echinoderms has been a research focus since the early twentieth century, consistently providing ever deeper knowledge of its complexity and evolutionary aspects. At its core are coelomocytes, which are diverse cells collectively known to respond in a variety of ways, including via movement, phagocytosis, and aggregation. However, features of cellular immunity have never been compared in echinoderms from phylogenetic and distributional perspectives, to provide insight into ecological and evolutionary patterns. The present study catalyzed and characterized the formation of coelomocyte aggregates in members of all five extant classes of echinoderms. The morphological characteristics of these aggregates (including their colour, shape, texture, size) were assessed, as well as the major cells composing them. Coelomocyte diversity (both as free and aggregated forms) was determined to be maximum in class Holothuroidea, followed by Echinoidea, with the other classes showing similar levels of diversity. The colours of coelomocyte aggregates appeared to be more closely linked to phylogeny (classes, orders) rather than geographic range, or external colour of the species themselves. Asteroids and ophiuroids displayed primarily light-coloured aggregates, from transparent to green; while holothuroids, echinoids and crinoids demonstrated more vivid variants, from red to deep purple. The kinetics of aggregate formation and expulsion were monitored in selected species, showing immediate cellular response to foreign particulate matter in the form of encapsulation and various methods of expulsion, including through the dermal papillae of asteroids and the anus (cloaca) of holothuroids. The findings support that coelomocyte aggregate formation is a conserved immune response across all five extant classes of echinoderms with variations in their cell catalysts, complexity, shape, colour, and size.

Galactose-Binding C-Type Lectin Promotes Cellular Aggregation of Coelomocytes in Sea Cucumber

Echinoderms have a large coelomic cavity containing coelomocytes. When the coelomic fluid is removed from the cavity, the cells aggregate immediately. We found that a fraction or an extract of the intestine of the sea cucumber, Apostichopus japonicus, markedly accelerated cellular movement and aggregation on a glass slide, and this effect was clearly inhibited by galactose. We successfully purified the aggregation-promoting factor, a 16 kDa protein, from the intestine. TOF-MS analysis followed by de novo sequencing revealed that the protein is a C-type lectin. RNA-seq data and cDNA cloning demonstrated the factor to be a novel lectin, named AjGBCL, consisting of 158 aa residues in the mature form. Microscopic observation revealed that most of the aggregating cells moved toward aggregates and not to an intestinal fragment, suggesting that AjGBCL is not a chemoattractant but a cellular aggregation-inducing factor that may induce aggregates to release chemoattractant. We report, for the first time, an endogenous molecule that promotes coelomocyte aggregation in echinoderms.

Colorless spherule cells and lysozyme contribute to innate immunological responses in the sea urchin Lytechinus variegatus, exposed to bacterial challenge

The sea urchin Lytechinus variegatus is considered a good candidate for aquaculture, but bacterial diseases are a major challenge in culture conditions. The innate immunological defenses of L. variegatus to bacterial challenges were assessed through hematology parameters, in vitro phagocytosis, lysozyme activity and total plasma protein concentrations in cell-free coelomic fluid. Adult sea urchins were inoculated with Microccocus lysodeikticus, Escherichia coli and Vibrio parahaemolyticus in the cavity coelomic. Filtrated and sterile seawater (FSW) injected and non-injected sea urchins were used as control groups. Righting time, external aspects and behavior of sea urchins were evaluated. Twenty-four hours post-inoculation, we found an increase in the population of colorless spherule cells (CLS), phagocytosis, and humoral responses in sea urchins challenged by bacterial inoculations. Righting time was not affected by the treatments and apparent external signs of disease were not observed at least during 96h post-inoculation. The immunological system of L. variegatus quickly eliminated pathogenic microorganisms. CLS and lysozyme activity cooperate in the immune defenses of L. variegatus, showing an extraordinary efficiency for adjusting the immune defenses under stress caused by microbes. We recommend that the cellular and humoral markers serve as routine tests to monitor health status in sea urchins.

Comparative study of coelomocytes from Arbacia lixula and Lythechinus variegatus: Cell characterization and in vivo evidence of the physiological function of vibratile cells

The knowledge on echinoderm coelomocytes has increased in recent years, but researchers still face a complex problem: how to obtain purified cells. Even flow cytometry being useful to address coelomocytes in suspension, the need for a method able to provide isolated cells is still noteworthy. Here, we use Imaging Flow Cytometry (IFC) to characterize the coelomocytes of two sea urchin species - Arbacia lixula and Lytechinus variegatus - and obtain gates to isolate cell populations. Then, we used these gates to study the physiological response of A. lixula coelomocytes during an induced immune challenge with Escherichia coli. An analysis of area and aspect ratio parameters of the flow cytometer allowed the identification of two main cell populations in the coelomic fluid: circular and elongated cells. A combination of this method with nucleus labeling using propidium iodide allowed the determination of gates containing isolated subpopulations of vibratile cells, red spherulocytes, and two phagocytes subpopulations in both species. We observed that during an induced bacterial immune challenge, A. lixula was able to modulate coelomocyte frequencies, increasing the phagocytes and decreasing red spherulocytes and vibratile cells. These results indicate that vibratile cells and red spherulocytes act by immobilizing and stoping bacterial growth, respectively, cooperating with phagocytes in the immune response. The use of IFC was fundamental not only to identify specific gates for the main coelomic subpopulations but also allowed the investigation on how echinoids modulate their physiological responses during immune challenges. Furthermore, we provide the first experimental evidence about the role of vibratile cells, corroborating its involvement with the immune system.

Effect of bacterial LPS, poly I:C and temperature on the immune response of coelomocytes in short term cultures of red sea urchin (Loxechinus albus)

In echinoderms, the immune system plays a relevant role in defense against infection by pathogens. Particularly, in sea urchins, the immune system has been shown to be complex, especially in terms of the variety of immune genes and molecules described. A key component of the response to external pathogens are the Toll-like receptors (TLRs), which are a well-characterized class of pattern recognition receptors (PRRs) that participate in the recognition of pathogen-associated molecular patterns (PAMPs). Despite the fact that TLRs have been described in several sea urchin species, for the red sea urchin (Loxechinus albus), which is one of the most important sea urchins across the world in terms of fisheries, limited information on the TLR-mediated immune response exists. In the present study, for the first time, we evaluated the effect of thermal stress, LPS and poly I:C treatment on the coelomocyte immune response of Loxechinus albus to determine how these factors modulate TLR and strongylocin (antimicrobial peptides of echinoderms) responses. We show that the tlr3-like, tlr4-like, tlr6-like and tlr8-like transcripts are modulated by poly I:C, while LPS only modulates the tlr4-like response; there was no effect of temperature on TLR expression, as evaluated by RT-qPCR. Additionally, we showed that strongylocin-1 and strongylocin-2 are modulated in response to simulated viral infection with poly I:C, providing the first evidence of strongylocin expression in L. albus. Finally, we determined that temperature and LPS modify the viability of coelomocytes, while poly I:C treatment did not affect the viability of these cells. This study contributes to the knowledge of immune responses in sea urchins to improve the understanding of the role of TLRs and strongylocins in echinoderms.

The Axial Organ and the Pharynx Are Sites of Hematopoiesis in the Sea Urchin

Background: The location of coelomocyte proliferation in adult sea urchins is unknown and speculations since the early 1800s have been based on microanatomy and tracer uptake studies. In adult sea urchins (Strongylocentrotus purpuratus) with down-regulated immune systems, coelomocyte numbers increase in response to immune challenge, and whether some or all of these cells are newly proliferated is not known. The gene regulatory network that encodes transcription factors that control hematopoiesis in embryonic and larval sea urchins has not been investigated in adults. Hence, to identify the hematopoietic tissue in adult sea urchins, cell proliferation, expression of phagocyte specific genes, and expression of genes encoding transcription factors that function in the conserved regulatory network that controls hematopoiesis in embryonic and larval sea urchins were investigated for several tissues. Results: Cell proliferation was induced in adult sea urchins either by immune challenge through injection of heat-killed Vibrio diazotrophicus or by cell depletion through aspiration of coelomic fluid. In response to either of these stimuli, newly proliferated coelomocytes constitute only about 10% of the cells in the coelomic fluid. In tissues, newly proliferated cells and cells that express SpTransformer proteins (formerly Sp185/333) that are markers for phagocytes are present in the axial organ, gonad, pharynx, esophagus, and gut with no differences among tissues. The expression level of genes encoding transcription factors that regulate hematopoiesis show that both the axial organ and the pharynx have elevated expression compared to coelomocytes, esophagus, gut, and gonad. Similarly, an RNAseq dataset shows similar results for the axial organ and pharynx, but also suggests that the axial organ may be a site for removal and recycling of cells in the coelomic cavity. Conclusions: Results presented here are consistent with previous speculations that the axial organ may be a site of coelomocyte proliferation and that it may also be a center for cellular removal and recycling. A second site, the pharynx, may also have hematopoietic activity, a tissue that has been assumed to function only as part of the intestinal tract.

Sea urchin Paracentrotus lividus immune cells in culture: formulation of the appropriate harvesting and culture media and maintenance conditions

The sea urchin is an emergent model system for studying basic and translational immunology. Here we report a new method for the harvesting and maintenance of primary immune cells isolated from adult Paracentrotus lividus, a common Mediterranean sea urchin species. This optimised method uses coelomocyte culture medium, containing a high-affinity Ca²⁺ chelator, as the ideal harvesting and anti-clotting vehicle and short-term culture medium (≤48 h), and artificial seawater as the master medium that maintains cell survival and in vitro-ex vivo physiological homeostasis over 2 weeks. Gradually reducing the amount of anticoagulant solution in the medium and regularly replacing the medium led to improved culture viability. Access to a robust and straightforward in vitro-ex vivo system will expedite our understanding of deuterostome immunity as well as underscore the potential of sea urchin with respect to biomedicine and regulatory testing.

This article has an associated First Person interview with the first author of the paper.

Summary: Appropriate culture methods for sea urchin immune cells provide an invaluable and amenable model for answering immunological questions while limiting the use of mammalian organisms.

Methods for collection, handling, and analysis of sea urchin coelomocytes

Sea urchin coelomocytes can be collected in large numbers from adult sea urchins of the species, Strongylocentrotus purpuratus, which typically has 12-40mL of coelomic fluid. Coelomocytes are used for analysis of immune reactions and immune gene expression in addition to basic functions of cells, in particular for understanding structure and modifications of the cytoskeleton in phagocytes. The methods described here include coelomocyte isolation, blocking the clotting reaction, establishing and maintaining primary cultures, separation of different types of coelomocytes into fractions, processing live coelomocytes for light microscopy, fixation and staining for light and electron microscopy, analysis of coelomocyte populations by flow cytometry, and sorting single cells for more detailed follow-up analyses including transcriptomics or genomic characteristics. These methods are provided to make working with coelomocytes accessible to researchers who are unfamiliar with these cells and perhaps to aid others who have worked extensively with invertebrate cells.

Echinometra mathaei and its ectocommensal shrimps: the role of sea urchin spinochrome pigments in the symbiotic association

Tuleariocaris holthuisi and Arete indicus are two ectocommensal shrimps closely associated with the tropical sea urchin Echinometra mathaei. This study provides a comparison of these two E. mathaei symbiotic crustaceans and particularly focuses on the relationship between T. holthuisi and its host's pigments (i.e. spinochromes), and its dependency on its host. While all the analyses underline a close association between A. indicus and E. mathaei, they reveal a particularly close interaction between T. holthuisi and its host. Chemical analyses reveal that these shrimps present the same spinochrome composition as E. mathaei, and have similar colouration, allowing camouflage. Isotopic composition and pigment loss after host separation suggest that these pigments are certainly assimilated upon feeding on the urchin. Moreover, symbiont isolation experiments demonstrate the high dependency of T. holthuisi on its host and the importance of the host's pigments on their survival capacity. Finally, some host recognition mechanisms are investigated for T. holthuisi and show the probable implication of spinochromes in host selection, through chemical recognition. Hence, all the results suggest the essential roles of spinochromes for T. holthuisi, which, in turn, suggests the potential implication of these pigments in the shrimps' metabolism.

Mapping of Spinochromes in the Body of Three Tropical Shallow Water Sea Urchins

Sea urchin pigments, also known as spinochromes or polyhydroxynaphthoquinones (PHNQ) have been well studied for their bioactive properties like anti-bacterial, fungicidal, antioxidant and pro-inflammatory effects. Moreover, many studies have analyzed and identified these pigments in sea urchin tests and spines but, and to the best of our knowledge, never in their body compartments or in a quantitative manner. The aim of this work was to investigate the diversity and concentration of pigments in three sea urchins localized in the same coral reef in Madagascar ( Diadema savignyi, Tripneustes gratilla and Toxopneustes pileolus). Their pigment distribution patterns were compared and linked to their behavior in order to understand better the implication of spinochromes in a sea urchin's life. Analyses and quantifications by LC-MS showed the presence of 11 different spinochromes with principally two kinds of patterns. First, D. savignyi showed a high concentration in all its body compartments with a predominance for Echinochrome A and Spinochrome D – Iso 3, a pattern close to the E. mathaei distribution found in our previous study. The presence of these pigments has been linked to their bioactive properties and suggested their implications in UV radiation protection, in reproduction, in feeding as well as in their immune systems. Secondly, T. gratilla and T. pileolus presented few spinochromes, which could explain their restricted diet and their covering behavior facing sunlight. Moreover, the absence of pigments in their gonads could be explained by their seasonal spawning occurring before our collection period. Nevertheless, the near absence of spinochromes may be counterbalanced by other bioactive compounds like their toxic proteins, which may act as either a defense mechanism or immune agents, or like carotenoid pigments already shown in sea urchin and acting as defense agents. In conclusion, spinochromes, and pigments in general, seem to play many roles in sea urchin ecology. Their highly reactive structures confer them with strong bioactive properties involved in most parts of their metabolic system and clearly participate in the survival of the sea urchins.

Identification and quantification of spinochromes in body compartments of Echinometra mathaei's coloured types

Sea urchin pigmentation is mainly due to polyhydroxy-1,4-naphthoquinones called spinochromes. If their molecular structures are well known in test and spines of many species, their abundance and distribution in other body compartments remain unstudied. The aim of this study is to analyse the pigment composition in four body compartments (test/spines, digestive system, gonads and coelomic fluid) of four coloured types of the sea urchin Echinometra mathaei. Qualitative and quantitative measurements by mass spectrometry highlight the existence of 13 different pigments; among which are five isomers of known spinochromes as well as three potentially new ones. The composition comparison shows the largest spinochrome diversity in 'test/spines' body compartments. The spinochrome concentrations vary from 48 to 1279 mg kg-1 of dried body compartment. It is the highest in the digestive system, although it is also important in the organic fraction of the 'test/spines' body compartment. This observation may be explained by higher exposures of some body compartments to external environments and by the protective role fulfilled by spinochromes against microorganisms, ultraviolet radiation and reactive oxygen species. The 'black' type-the most common coloured type in coral reefs-has the highest concentration of spinochromes indicating their importance in Echinoids' fitness by acting as a protective agent.

SpTransformer proteins from the purple sea urchin opsonize bacteria, augment phagocytosis, and retard bacterial growth

The purple sea urchin, Strongylocentrotus purpuratus, has a complex and robust immune system that is mediated by a number of multi-gene families including the SpTransformer (SpTrf) gene family (formerly Sp185/333). In response to immune challenge from bacteria and various pathogen-associated molecular patterns, the SpTrf genes are up-regulated in sea urchin phagocytes and express a diverse array of SpTrf proteins. We show here that SpTrf proteins from coelomocytes and isolated by nickel affinity (cNi-SpTrf) bind to Gram-positive and Gram-negative bacteria and to Baker's yeast, Saccharomyces cerevisiae, with saturable kinetics and specificity. cNi-SpTrf opsonization of the marine bacteria, Vibrio diazotrophicus, augments phagocytosis, however, opsonization by the recombinant protein, rSpTrf-E1, does not. Binding by cNi-SpTrf proteins retards growth rates significantly for several species of bacteria. SpTrf proteins, previously thought to be strictly membrane-associated, are secreted from phagocytes in short term cultures and bind V. diazotrophicus that are located both outside of and within phagocytes. Our results demonstrate anti-microbial activities of native SpTrf proteins and suggest variable functions among different SpTrf isoforms. Multiple isoforms may act synergistically to detect a wide array of pathogens and provide flexible and efficient host immunity.

Echinochrome A Release by Red Spherule Cells Is an Iron-Withholding Strategy of Sea Urchin Innate Immunity

Cellular immune defences in sea urchins are shared amongst the coelomocytes - a heterogeneous population of cells residing in the coelomic fluid (blood equivalent) and tissues. The most iconic coelomocyte morphotype is the red spherule cell (or amebocyte), so named due to the abundance of cytoplasmic vesicles containing the naphthoquinone pigment echinochrome A. Despite their identification over a century ago, and evidence of antiseptic properties, little progress has been made in characterising the immunocompetence of these cells. Upon exposure of red spherule cells from sea urchins, i.e., Paracentrotus lividus and Psammechinus miliaris, to microbial ligands, intact microbes, and damage signals, we observed cellular degranulation and increased detection of cell-free echinochrome in the coelomic fluid ex vivo. Treatment of the cells with ionomycin, a calcium-specific ionophore, confirmed that an increase in intracellular levels of Ca2+ is a trigger of echinochrome release. Incubating Gram-positive/negative bacteria as well as yeast with lysates of red spherule cells led to significant reductions in colony-forming units. Such antimicrobial properties were counteracted by the addition of ferric iron (Fe3+), suggesting that echinochrome acts as a primitive iron chelator in echinoid biological defences.

ABCB1 and ABCC1-like transporters in immune system cells from sea urchins Echinometra lucunter and Echinus esculentus and oysters Crassostrea gasar and Crassostrea gigas

ABC transporters activity and expression have been associated with the multixenobiotic resistance phenotype (MXR). The activity of these proteins leads to a reduction in the intracellular concentration of several xenobiotics, thus reducing their toxicity. However, little attention has been given to the expression of ABC transporters in marine invertebrates and few studies have investigated their role in immune system cells of sea urchins and shellfish bivalves. The aim of the present study was to investigate the activity of the ABC transporters ABCB1 and ABCC1 in immune system cells of sea urchins (coelomocytes) and oysters (hemocytes) from different climatic regions (Brazil and France). Sea urchins and oysters were collected at Paraíba coast; Brazil (Echinometra lucunter and Crassostrea gasar) and Rade of Brest; France (Echinus esculentus and Crassostrea gigas). Coelomocytes and hemocytes were stained with the ABC transporter substrate calcein-AM and dye accumulation analyzed under flow cytometry. Reversin 205 (ABCB1 transporter blocker) and MK571 (ABCC1 transporter blocker) were used as pharmacological tools to investigate ABC transporter activity. A different pattern of calcein accumulation was observed in coelomocytes: phagocytes > colorless spherulocytes > vibrate cells > red spherulocytes. The treatment with MK571 increased calcein fluorescence levels in coelomocytes from both species. However, reversin 205 treatment was not able to increase calcein fluorescence in E. esculentus coelomocytes. These data suggest that ABCC1-like transporter activity is present in both sea urchin species, but ABCB1-like transporter activity might only be present in E. lucunter coelomocytes. The activity of ABCC1-like transporter was observed in all cell types from both bivalve species. However, reversin 205 only increased calcein accumulation in hyalinocytes of the oyster C. gasar, suggesting the absence of ABCB1-like transporter activity in all other cell types, including hyalinocytes from the oyster C. gigas. Additionally, our results showed that C. gigas exhibited higher activity of ABCC1-like transporter in all hemocyte types than C. gasar. The present work is the first to characterize ABCB1 and ABCC1-like transporter activity in the immune system cells of sea urchins E. lucunter and E. esculentus and oysters. Our findings encourage the performing studies regarding ABC transporters activity/expression in immune system cells form marine invertebrates under stress conditions and the possible use of ABC transporters as biomarkers.

The SpTransformer Gene Family (Formerly Sp185/333) in the Purple Sea Urchin and the Functional Diversity of the Anti-Pathogen rSpTransformer-E1 Protein

The complex innate immune system of sea urchins is underpinned by several multigene families including the SpTransformer family (SpTrf; formerly Sp185/333) with estimates of ~50 members, although the family size is likely variable among individuals of Strongylocentrotus purpuratus. The genes are small with similar structure, are tightly clustered, and have several types of repeats in the second of two exons and that surround each gene. The density of repeats suggests that the genes are positioned within regions of genomic instability, which may be required to drive sequence diversification. The second exon encodes the mature protein and is composed of blocks of sequence called elements that are present in mosaics of defined element patterns and are the major source of sequence diversity. The SpTrf genes respond swiftly to immune challenge, but only a single gene is expressed per phagocyte. Many of the mRNAs appear to be edited and encode proteins with altered and/or missense sequence that are often truncated, of which some may be functional. The standard SpTrf protein structure is an N-terminal glycine-rich region, a central RGD motif, a histidine-rich region, and a C-terminal region. Function is predicted from a recombinant protein, rSpTransformer-E1 (rSpTrf-E1), which binds to Vibrio and Saccharomyces, but not to Bacillus, and binds tightly to lipopolysaccharide, β-1,3-glucan, and flagellin, but not to peptidoglycan. rSpTrf-E1 is intrinsically disordered but transforms to α helical structure in the presence of binding targets including lipopolysaccharide, which may underpin the characteristics of binding to multiple targets. SpTrf proteins associate with coelomocyte membranes, and rSpTrf-E1 binds specifically to phosphatidic acid (PA). When rSpTrf-E1 is bound to PA in liposome membranes, it induces morphological changes in liposomes that correlate with PA clustering and leakage of luminal contents, and it extracts or removes PA from the bilayer. The multitasking activities of rSpTrf-E1 infer multiple and perhaps overlapping activities for the hundreds of native SpTrf proteins that are produced by individual sea urchins. This likely generates a flexible and highly protective immune system for the sea urchin in its marine habitat that it shares with broad arrays of microbes that may be pathogens and opportunists.

The Roles of Spinochromes in Four Shallow Water Tropical Sea Urchins and Their Potential as Bioactive Pharmacological Agents

Spinochromes are principally known to be involved in sea urchin pigmentation as well as for their potentially interesting pharmacological properties. To assess their biological role in sea urchin physiology, experiments are undertaken on crude extracts from four species and on four isolated spinochromes in order to test their antibacterial, antioxidant, inflammatory and cytotoxic activities. First, the antibacterial assays show that the use of crude extracts as representatives of antibacterial effects of spinochromes are inaccurate. The assays on purified spinochromes showed a decrease in the growth of four strains with an intensity depending on the spinochromes/bacteria system, revealing the participation of spinochromes in the defense system against microorganisms. Secondly, in the 2,2-diphenyl-1-picrylhydrazyl antioxidant assays, spinochromes show an enhanced activity compared to the positive control. This latter observation suggests their involvement in ultraviolet radiation protection. Third, spinochromes present a pro-inflammatory effect on lipopolysaccharide-stimulated macrophages, highlighting their possible implication in the sea urchin immune system. Finally, cytotoxicity assays based on Trypan blue exclusion, performed in view of their possible future applications as drugs, show a weak cytotoxicity of these compounds against human cells. In conclusion, all results confirm the implication of spinochromes in sea urchin defense mechanisms against their external environment and reveal their potential for pharmacological and agronomical industries.

Differential count and time-course analysis of the cellular composition of coelomocyte aggregate of the Japanese sea cucumber Apostichopus japonicus

Echinoderms have many types of coelomocytes, which have been known to form aggregates immediately after they are removed from the coelom. To assess the roles that each type of coelomocyte plays in aggregate formation, cellular components of coelomocyte aggregates of the Japanese sea cucumber, Apostichopus japonicus, were investigated. The coelomocytes were tentatively classified into 12 types based on May-Grunwald/Giemsa staining. After the coelom was incubated for 30 min or 6 h, the aggregates were disaggregated completely with 200 mM EDTA. Differential counts of the dissociated cells indicated that the largest component of the aggregates was amoebocytes (67.8%) and the second-largest component of the aggregates incubated 30 min was a type of basophilic granulocyte. In the 6h-incubated aggregates, the fraction of amoebocytes decreased to 59.0%, while that of lymphoid cells significantly increased, which suggests that lymphoid cells participate in late-stage aggregation. After 24-h incubation, only a portion of the aggregated cells could be disaggregated with EDTA. After 48 h, most of the cells could not be detached from the aggregates. Microscopy of frozen sections of the aggregates after 6-h incubation revealed that amoebocytes constructed a mesh-like structure to which other types of cells adhered. After 48 h, the borders of the cells and the intracellular granules were not recognizable. In time-lapse microscopy, the aggregates were observed to move on a glass slide, which suggests that aggregates can "crawl" on the intraluminal surface of the coelom toward, for example, injured regions in the body of the sea cucumber.

Sea urchin immune cells as sentinels of environmental stress

Echinoderms, an ancient and very successful phylum of marine invertebrates, play a central role in the maintenance of ecosystem integrity and are constantly exposed to environmental pressure, including: predation, changes in temperature and pH, hypoxia, pathogens, UV radiation, metals, toxicants, and emerging pollutants like nanomaterials. The annotation of the sea urchin genome, so closely related to humans and other vertebrate genomes, revealed an unusually complex immune system, which may be the basis for why sea urchins can adapt to different marine environments and survive even in hazardous conditions. In this review, we give a brief overview of the morphological features and recognized functions of echinoderm immune cells with a focus on studies correlating stress and immunity in the sea urchin. Immune cells from adult Paracentrotus lividus, which have been introduced in the last fifteen years as sentinels of environmental stress, are valid tools to uncover basic molecular and regulatory mechanisms of immune responses, supporting their use in immunological research. Here we summarize laboratory and field studies that reveal the amenability of sea urchin immune cells for toxicological testing.

Single sea urchin phagocytes express messages of a single sequence from the diverse Sp185/333 gene family in response to bacterial challenge

Immune systems in animals rely on fast and efficient responses to a wide variety of pathogens. The Sp185/333 gene family in the purple sea urchin, Strongylocentrotus purpuratus, consists of an estimated 50 (±10) members per genome that share a basic gene structure but show high sequence diversity, primarily due to the mosaic appearance of short blocks of sequence called elements. The genes show significantly elevated expression in three subpopulations of phagocytes responding to marine bacteria. The encoded Sp185/333 proteins are highly diverse and have central effector functions in the immune system. In this study we report the Sp185/333 gene expression in single sea urchin phagocytes. Sea urchins challenged with heat-killed marine bacteria resulted in a typical increase in coelomocyte concentration within 24 h, which included an increased proportion of phagocytes expressing Sp185/333 proteins. Phagocyte fractions enriched from coelomocytes were used in limiting dilutions to obtain samples of single cells that were evaluated for Sp185/333 gene expression by nested RT-PCR. Amplicon sequences showed identical or nearly identical Sp185/333 amplicon sequences in single phagocytes with matches to six known Sp185/333 element patterns, including both common and rare element patterns. This suggested that single phagocytes show restricted expression from the Sp185/333 gene family and infers a diverse, flexible, and efficient response to pathogens. This type of expression pattern from a family of immune response genes in single cells has not been identified previously in other invertebrates.

Expression of antimicrobial peptides in coelomocytes and embryos of the green sea urchin (Strongylocentrotus droebachiensis)

Antimicrobial peptides (AMPs) play a crucial role in innate immunity. We have previously reported the isolation and characterization of the AMPs, strongylocins 1 and 2, and centrocin 1, from coelomocyte extracts of Strongylocentrotus droebachiensis. Here we show that these AMPs were expressed in phagocytes. In addition, transcripts of strongylocin 1 were detected in vibratile cells and/or colorless spherule cells, while transcripts of strongylocin 2 were found in red spherule cells. Results from immunoblotting and immunocytochemistry studies showed that centrocin 1 was produced by phagocytes and stored in granular vesicles. Co-localization of centrocin 1 and phagocytosed bacteria suggests that the granular vesicles containing centrocin 1 may be involved in the formation of phagolysosomes. We also analyzed the temporal and spatial expression of AMPs throughout larval development. Strongylocins were expressed in the early pluteus stage, while centrocin 1 was expressed in the mid pluteus stage. The spatial expression pattern showed that centrocin 1 was mainly located in blastocoelar cells (BCs) around the stomach and the esophagus. In addition, a few patrolling BCs were detected in some larval arms. Together, these results suggest that AMPs are expressed in different types of coelomocytes and that centrocin 1 is involved in response against bacteria. Furthermore, the expression of AMPs in larval pluteus stage, especially in BCs, indicates that AMPs and BCs are engaged in the larval immune system.