Increased expression of the potential proapoptotic molecule DD2 and increased synthesis of leukotriene B4 during allograft rejection in a marine sponge

Induction of apoptosis by double-stranded RNA was present in the last common ancestor of cnidarian and bilaterian animals

Apoptosis, a major form of programmed cell death, is an essential component of host defense against invading intracellular pathogens. Viruses encode inhibitors of apoptosis to evade host responses during infection, and to support their own replication and survival. Therefore, hosts and their viruses are entangled in a constant evolutionary arms race to control apoptosis. Until now, apoptosis in the context of the antiviral immune system has been almost exclusively studied in vertebrates. This limited phyletic sampling makes it impossible to determine whether a similar mechanism existed in the last common ancestor of animals. Here, we established assays to probe apoptosis in the sea anemone Nematostella vectensis, a model species of Cnidaria, a phylum that diverged approximately 600 million years ago from the rest of animals. We show that polyinosinic:polycytidylic acid (poly I:C), a synthetic long double-stranded RNA mimicking viral RNA and a primary ligand for the vertebrate RLR melanoma differentiation-associated protein 5 (MDA5), is sufficient to induce apoptosis in N. vectensis. Furthermore, at the transcriptomic level, apoptosis related genes are significantly enriched upon poly(I:C) exposure in N. vectensis as well as bilaterian invertebrates. Our phylogenetic analysis of caspase family genes in N. vectensis reveals conservation of all four caspase genes involved in apoptosis in mammals and revealed a cnidarian-specific caspase gene which was strongly upregulated. Altogether, our findings suggest that apoptosis in response to a viral challenge is a functionally conserved mechanism that can be traced back to the last common ancestor of Bilateria and Cnidaria.

Molecular machineries of ciliogenesis, cell survival, and vasculogenesis are differentially expressed during regeneration in explants of the demosponge Halichondria panicea

Sponges are interesting animal models for regeneration studies, since even from dissociated cells, they are able to regenerate completely. In particular, explants are model systems that can be applied to many sponge species, since small fragments of sponges can regenerate all elements of the adult, including the oscula and the ability to pump water. The morphological aspects of regeneration in sponges are relatively well known, but the molecular machinery is only now starting to be elucidated for some sponge species. Here, we have used an explant system of the demosponge Halichondria panicea to understand the molecular machinery deployed during regeneration of the aquiferous system. We sequenced the transcriptomes of four replicates of the 5-day explant without an osculum (NOE), four replicates of the 17-18-day explant with a single osculum and pumping activity (PE) and also four replicates of field-collected individuals with regular pumping activity (PA), and performed differential gene expression analysis. We also described the morphology of NOE and PE samples using light and electron microscopy. Our results showed a highly disorganised mesohyl and disarranged aquiferous system in NOE that is coupled with upregulated pathways of ciliogenesis, organisation of the ECM, and cell proliferation and survival. Once the osculum is formed, genes involved in "response to stimulus in other organisms" were upregulated. Interestingly, the main molecular machinery of vasculogenesis described in vertebrates was activated during the regeneration of the aquiferous system. Notably, vasculogenesis markers were upregulated when the tissue was disorganised and about to start forming canals (NOE) and angiogenic stimulators and ECM remodelling machineries were differentially expressed once the aquiferous system was in place (PE and PA). Our results are fundamental to better understanding the molecular mechanisms involved in the formation of the aquiferous system in sponges, and its similarities with the early onset of blood-vessel formation in animal evolution.

Sponges: A Reservoir of Genes Implicated in Human Cancer

Recently, it was shown that the majority of genes linked to human diseases, such as cancer genes, evolved in two major evolutionary transitions—the emergence of unicellular organisms and the transition to multicellularity. Therefore, it has been widely accepted that the majority of disease-related genes has already been present in species distantly related to humans. An original way of studying human diseases relies on analyzing genes and proteins that cause a certain disease using model organisms that belong to the evolutionary level at which these genes have emerged. This kind of approach is supported by the simplicity of the genome/proteome, body plan, and physiology of such model organisms. It has been established for quite some time that sponges are an ideal model system for such studies, having a vast variety of genes known to be engaged in sophisticated processes and signalling pathways associated with higher animals. Sponges are considered to be the simplest multicellular animals and have changed little during evolution. Therefore, they provide an insight into the metazoan ancestor genome/proteome features. This review compiles current knowledge of cancer-related genes/proteins in marine sponges.

Transcriptome analysis of the immune reaction of the pearl oyster Pinctada fucata to xenograft from Pinctada maxima

The pearl oyster Pinctada maxima exhibits great difficulty to culture pearls through nuclear insertion with an allograft, but it is easy for P. fucata to culture pearls after allografting. If P. fucata could be used as a surrogate mother to culture P. maxima pearls, it would benefit the pearl culture industry of P. maxima. However, this is blocked by the immune rejection of P. fucata against P. maxima mantle grafts. In this study, the immune responses of P. fucata hemocyte to allograft and xenograft were investigated after transplantation by transcriptome analysis. In total, 107.93 Gb clean reads were produced and assembled using the reference genome of P. fucata. Gene Ontology Term enrichment and KEGG enrichment analyses indicated that apoptosis, hippo signaling pathway, oxidation-reduction, MAPK signaling pathway, ribosome, protein processing in endoplasmic reticulum, purine metabolism, NF-kappa B signaling pathway, oxidative phosphorylation, Ras signaling pathway, and ubiquitin mediated proteolysis were involved in response to transplantation. Many genes related to oxidation-reduction reactions, the MAPK signaling pathway, and apoptosis were identified by comparison of the allograft group and the xenograft group at 0 h, 6 h, 12 h, 24 h, 48 h, 72 h, and 96 h post-transplantation. Among them, the expression levels of NADH dehydrogenase, succinate dehydrogenase and other dehydrogenases were increased significantly in the xenograft groups compared with allograft groups at 0 h post transplantation, indicating that a respiratory burst of neutrophils occurred immediately after xenograft transplantation. Additionally, HSP70 was highly expressed from 0 h to 96 h in the xenograft groups, indicating an oyster immune response to the xenograft. The genes enriched in the ribosome and hippo-signaling pathways were also identified, and expression patterns of these DEGs were different as compared between transplantation and control groups. Finally, altered expression levels of 10 randomly selected immune-related DEGs were confirmed by quantitative real-time PCR. These results indicated that oxidation-reduction is likely the key factor responsible for immune rejection to transplantation. The findings should provide some new insight into the molecular mechanism of immune rejection of the host against xenograft, and thus benefit to development of immunosuppressive reagents to facilitate effective xenograft pearling.

Transcriptomic Profiling of the Allorecognition Response to Grafting in the Demosponge Amphimedon queenslandica

Sponges, despite their simple body plan, discriminate between self and nonself with remarkable specificity. Sponge grafting experiments simulate the effects of natural self or nonself contact under laboratory conditions. Here we take a transcriptomic approach to investigate the temporal response to self and nonself grafts in the marine demosponge Amphimedon queenslandica. Auto- and allografts were established, observed and sampled over a period of three days, over which time the grafts either rejected or accepted, depending on the identity of the paired individuals, in a replicable and predictable manner. Fourteen transcriptomes were generated that spanned the auto- and allograft responses. Self grafts fuse completely in under three days, and the process appears to be controlled by relatively few genes. In contrast, nonself grafting results in a complete lack of fusion after three days, and appears to involve a broad downregulation of normal biological processes, rather than the mounting of an intense defensive response.

Evolution of the animal apoptosis network

The number of available eukaryotic genomes has expanded to the point where we can evaluate the complete evolutionary history of many cellular processes. Such analyses for the apoptosis regulatory networks suggest that this network already existed in the ancestor of the entire animal kingdom (Metazoa) in a form more complex than in some popular animal model organisms. This supports the growing realization that regulatory networks do not necessarily evolve from simple to complex and that the relative simplicity of these networks in nematodes and insects does not represent an ancestral state, but is the result of secondary simplifications. Network evolution is not a process of monotonous increase in complexity, but a dynamic process that includes lineage-specific gene losses and expansions, protein domain reshuffling, and emergence/reemergence of similar protein architectures by parallel evolution. Studying the evolution of such networks is a challenging yet interesting subject for research and investigation, and such studies on the apoptosis networks provide us with interesting hints of how these networks, critical in so many human diseases, have developed.

Cell death and renewal during prey capture and digestion in the carnivorous sponge Asbestopluma hypogea (Porifera: Poecilosclerida)

The sponge Asbestopluma hypogea is unusual among sponges due to its peculiar carnivorous feeding habit. During various stages of its nutrition cycle, the sponge is subjected to spectacular morphological modifications. Starved animals are characterized by many elongated filaments which are crucial for the sponge to capture prey. After capture, and during the digestion process, these filaments actively regress before being regenerated during a subsequent period of starvation. Here, we demonstrate that these morphological events repose on a highly dynamic cellular turnover implying a coordinated sequence of programmed cell death (apoptosis and autophagy), cell proliferation and cell migration. A candidate niche for cell renewal by stem cell proliferation and differentiation was identified at the base of the sponge peduncle, characterized by surpassing levels of BrdU/EdU incorporation. Therefore, BrdU/EdU positive-cells of the peduncle base are candidate motile cells responsible for the regeneration of the prey-capturing main sponge body, i.e. the dynamic filaments. Altogether, our results demonstrate that dynamic of cell renewal in sponge appears to be regulated by cellular mechanisms as multiple and complex as those already identified in bilaterian metazoans.

Living with death: the evolution of the mitochondrial pathway of apoptosis in animals

The mitochondrial pathway of cell death, in which apoptosis proceeds following mitochondrial outer membrane permeabilization, release of cytochrome c, and APAF-1 apoptosome-mediated caspase activation, represents the major pathway of physiological apoptosis in vertebrates. However, the well-characterized apoptotic pathways of the invertebrates C. elegans and D. melanogaster indicate that this apoptotic pathway is not universally conserved among animals. This review will compare the role of the mitochondria in the apoptotic programs of mammals, nematodes, and flies, and will survey our knowledge of the apoptotic pathways of other, less familiar model organisms in an effort to explore the evolutionary origins of the mitochondrial pathway of apoptosis.

Differential effect of allorecognition loci on phenotype in Hydractinia symbiolongicarpus (Cnidaria: Hydrozoa)

The allorecognition complex of Hydractinia symbiolongicarpus is a chromosomal interval containing two loci, alr1 and alr2, that controls fusion between genetically distinct colonies. Recombination between these two loci has been associated with a heterogeneous class of phenotypes called transitory fusion. A large-scale backcross was performed to generate a population of colonies (N = 106) with recombination breakpoints within the allorecognition complex. Two distinct forms of transitory fusion were correlated with reciprocal recombination products, suggesting that alr1 and alr2 contributed differentially to the allorecognition response. Specifically, type I transitory fusion is associated with rapid and persistent separation of allogeneic tissues, whereas type II transitory fusion generates a patchwork of continuously fusing and separating tissues.

Sponge disease: a global threat?

Sponges are the most simple and primitive metazoans, yet they have various biological and ecological properties that make them an influential component of coral-reef ecosystems. Marine sponges provide refuge for many small invertebrates and are critical to benthic-pelagic coupling across a wide range of habitats. Reports of sponge disease have increased dramatically in recent years with sponge populations decimated throughout the Mediterranean and Caribbean. Reports also suggest an increased prevalence of sponge disease in Papua New Guinea, the Great Barrier Reef and in the reefs of Cozumel, Mexico. These epidemics can have severe impacts on the survival of sponge populations, the ecology of the reef and the fate of associated marine invertebrates. Despite the ecological and commercial importance of sponges, the understanding of sponge disease is limited. There has generally been a failure to isolate and identify the causative agents of sponge disease, with only one case confirming Koch's postulates and identifying a novel Alphaproteobacteria strain as the primary pathogen. Other potential disease agents include fungi, viruses, cyanobacteria and bacterial strains within the Bacillus and Pseudomonas genera. There is some evidence for correlations between sponge disease and environmental factors such as climate change and urban/agricultural runoff. This review summarizes the occurrence of sponge disease, describes the syndromes identified thus far, explores potential linkages with environmental change and proposes a strategy for future research towards better management of sponge disease outbreaks.

Perforin-Dependent Cell Death in Skin Allograft Rejection of the Terrestrial Slug Incilaria fruhstorferi

The rejection of allografts in mammals is mainly mediated by cytotoxic T-lymphocytes, whereas no comparable immunoreactive cells have been described in invertebrates. The present study was undertaken to determine whether similar cytotoxic effector cells are present when allograft rejection occurs in the terrestrial slug Incilaria fruhstorferi. A piece of dorsal skin from a donor animal was orthotopically transplanted to a recipient. Immunohistochemistry for perforin, detection of apoptosis by the TUNEL (TdT-mediated dUTP-biotin nick-end labeling) method, and electron microscopy were performed using both donor and recipient tissues. Cellular changes in the rejection process continued over for 40 days. Two functional types of "effector" cells were recognized at the rejection site, but they were observed to be macrophages possessing perforin granules and phagocytosing damaged cells of the allograft. Three days after transplantation, the perforin-positive cells were recognized only in the recipient tissue surrounding the allograft. Five days after transplantation, these cells started to appear in the graft, while they disappeared from the host tissue. However, TUNEL-positive cells were not observed throughout the graft-rejection process. Electron microscopic examination of the graft tissue revealed autophagic degeneration of epithelial cells, mucous cells, pigment cells, fibroblasts, and muscle cells. These observations suggest that the molluscan slug has the capability to recognize differences in cell-surface molecules between the allogeneic and recipient tissues, and that an allograft is chronically rejected due to a type of immunocyte that can induce perforin-dependent cell death.

Axial (apical-basal) expression of pro-apoptotic and pro-survival genes in the lake baikal demosponge Lubomirskia baicalensis

Like in all other Metazoa, also in sponges (Porifera) proliferation, differentiation, and death of cells are controlled by apoptotic processes, thus allowing the establishment of a Bauplan (body plan). The demosponge Lubomirskia baicalensis from the Lake Baikal is especially suitable to assess the role of the apoptotic molecules, since its grade of construction is highly elaborated into an encrusting base and branches composed of modules lined up along the apical-basal axis. The four cDNAs, ALG-2, BAK, MA-3, and Bcl-2, were isolated from this sponge species. The expression levels of these genes follow characteristic gradients. While the proapoptotic genes are highly expressed at the base of the branches and comparably low at the top, the pro-survival gene follows an opposite gradient. Parallel with the tuned expression of these genes, the activities of the apoptosis-executing enzymes caspase-8 (IETDase activity) and caspase-3 (DEVDase activity) are lowest at the top of the branch and highest at their base. This characteristic expression/activity pattern of the genes/enzymes, which had been determined in a few specimens, collected from an unpolluted, natural site, appears reversed in specimens collected from an anthropogenically polluted site. These findings indicate the involvement of apoptotic proteins in the axis formation (branches) in L. baicalensis.

Evolution of the heart from bacteria to man

This review provides an overview of the evolutionary path to the mammalian heart from the beginnings of life (about four billion years ago ) to the present. Essential tools for cellular homeostasis and for extracting and burning energy are still in use and essentially unchanged since the appearance of the eukaryotes. The primitive coelom, characteristic of early multicellular organisms ( approximately 800 million years ago), is lined by endoderm and is a passive receptacle for gas exchange, feeding, and sexual reproduction. The cells around this structure express genes homologous to NKX2.5/tinman, and gradual specialization of this "gastroderm" results in the appearance of mesoderm in the phylum Bilateria, which will produce the first primitive cardiac myocytes. Investment of the coelom by these mesodermal cells forms a "gastrovascular" structure. Further evolution of this structure in the bilaterian branches Ecdysoa (Drosophila) and Deuterostoma (amphioxus) culminate in a peristaltic tubular heart, without valves, without blood vessels or blood, but featuring a single layer of contracting mesoderm. The appearance of Chordata and subsequently the vertebrates is accompanied by a rapid structural diversification of this primitive linear heart: looping, unidirectional circulation, an enclosed vasculature, and the conduction system. A later innovation is the parallel circulation to the lungs, followed by the appearance of septa and the four-chambered heart in reptiles, birds, and mammals. With differentiation of the cardiac chambers, regional specialization of the proteins in the cardiac myocyte can be detected in the teleost fish and amphibians. In mammals, growth constraints are placed on the heart, presumably to accommodate the constraints of the body plan and the thoracic cavity, and adult cardiac myocytes lose the ability to re-enter the cell cycle on demand. Mammalian cardiac myocyte innervation betrays the ancient link between the heart, the gut, and reproduction: the vagus nerve controlling heart rate emanates from centers in the central nervous system regulating feeding and affective behavior.

Report on the 14th Annual Meeting of the German Society for Geriatric Research

Members of the German Society for Geriatric Research (Deutsche Gesellschaft für Alternsforschung) and various invited speakers met in Karlsruhe, Germany, in November 2004 to discuss new findings and exchange views on intriguing problems in the broad field of aging research. This report summarizes some of the diverse topics that arose at the meeting, including diapause in insects, mitochondrial morphology in fungi, the production of reactive oxygen species, neurogenesis, and age-dependent changes of the cardiac system in mammals.

Allograft rejection in the mixed cell reaction system of the demosponge Suberites domuncula is controlled by differential expression of apoptotic genes

Until recently, the lack of molecular probes hampered the determination of the expression of pro-apoptotic and anti-apoptotic genes in sponge. In an approach to solve this problem, the present study describes a variety of cDNAs from the demosponge Suberites domuncula, coding for proteins that are characteristic for the initiation of apoptosis (caspase, MA3, ALG-2 protein), for the prevention of programmed cells death (2 Bcl-2 homology proteins, FAIM-related polypeptide, and DAD-1-related protein), and for morphogenetic processes (retinoid X receptor). They were used as probes to monitor the expression levels in vitro in the allogeneic mixed sponge cell reaction (MSCR) system. In the allogeneic MSCR, two-cell aggregates (primmorphs) from genetically different animals of the same species were positioned next to each other. After approximately 8 days in culture, one of the primmorphs underwent apoptotic death, while the second remained alive. The expression levels of the aforementioned genes were determined by Northern blotting and by in situ hybridization. These experiments revealed that in the apoptotic primmorph, the characteristic apoptotic genes were expressed, while in the non-apoptotic aggregates the cell-survival genes are highly upregulated. Interestingly, the transcript levels of retinoid X receptor were higher in apoptotic primmorphs than in the non-apoptotic aggregate in the assay. Our data show for the first time that in the in vitro MSCR system, allogeneic recognition led to apoptotic cell death in one partner, while the other one survived. We suggest that this process is controlled by a differential expression of the pro-apoptotic and pro-survival genes studied here.

Bauplan of Urmetazoa: Basis for Genetic Complexity of Metazoa

Sponges were first grouped to the animal-plants or plant-animals then to the Zoophyta or Mesozoa and finally to the Parazoa. Only after the application of molecular biological techniques was it possible to place the Porifera monophyletically with the other metazoan phyla, justifying a unification of all multicellular animals to only one kingdom, the Metazoa. The first strong support came from the discovery that cell-cell and cell-matrix adhesion molecules that were cloned from sponges and were subsequently expressed share a high DNA sequence and protein function similarity with the corresponding molecules of other metazoans. Besides these evolutionary novelties for Metazoa, sponges also have morphogens and transcription factors in common with other metazoan phyla. Surprisingly, even those elements exist in Porifera, which are characteristic for pattern and axis formation. Recent studies showed that epithelial layers of sponges are sealed against the extracellular milieu through tight-junction proteins. The cell culture system from sponges, the primmorphs, was suitable for understanding morphogenetic events. Finally, stem cell marker genes were isolated, which underscored that sponge cells have the capacity to differentiate. In the relatively short period of time, approximately 200 million years, the basic pathways had to be established that allowed the transition for multicellular organisms to a colonial system through the formation of adhesion molecules; based on the development of a complex immune system and the apoptotic machinery of an integrated system, the Urmetazoa, which evolved approximately 800 million years ago, could be reached. Hence, the Bauplan of the hypothetical Urmetazoa can now be constructed according to genomic regulatory systems similar to those found in higher Metazoa. These data caused a paradigmatic change; the Porifera are complex and simple but by far not primitive.

Caspase-mediated apoptosis in sponges: cloning and function of the phylogenetic oldest apoptotic proteases from Metazoa

Sponges (phylum Porifera) represent the phylogenetically oldest metazoan phylum. These animals have complex cell adhesion and powerful immune systems which allow the formation of a distinct body plan. Consequently, an apoptotic machinery has to be predicted that allows sponges to eliminate unwanted cells accumulating during development. With the marine sponge Geodia cydonium, it is shown that allografts of these animals undergo apoptosis as demonstrated by apoptotic DNA fragmentation. Extracts from allografts contain an enzymic activity characteristic for caspases; as substrate to determine the cleavage activity, Ac-DEVD-AMC was applied. cDNAs encoding predicted caspase-3-related proteins were isolated; they comprise the characteristic structure known from caspases of other metazoan phyla. The two cDNAs are assumed to originate from one gene by alternative splicing; the longer form comprises a caspase recruitment domain (CARD), whereas the shorter one is missing CARD. The expression of sponge caspase genes is up-regulated during allograft rejection. In vivo incubation experiments with Ac-DEVD-CHO (a caspase-3 inhibitor) showed a reduction of apoptotic DNA fragmentation, whereas Ac-LEHD-CHO (an inhibitor of caspase-9) caused no effect. It is concluded, that for the establishment of the metazoan body plan, both the adhesion molecules and the apoptotic molecules (described here) were essential prerequisites.

Analysis of the sponge [Porifera] gene repertoire: implications for the evolution of the metazoan body plan

Sponges [phylum Porifera] form the basis of the metazoan kingdom and represent the evolutionary earliest phylum still extant. Hence, as living fossils, they are the taxon closest related to the hypothetical ancestor of all Metazoa, the Urmetazoa. Until recently, it was still unclear whether sponges are provided with a defined body plan. Only after the cloning, expression and functional studies of characteristic metazoan genes, could it be demonstrated that these animals comprise the structural elements which allow the sponge cells to organize themselves according to a body plan. Adhesion molecules involved in cell-cell and cell-matrix interactions have been identified. Among the cell-cell adhesion molecules the aggregation factor (AF) is the prominent particle. It is composed of a core protein that is associated with the adhesion molecules, a 36 kDa as well as a 86 kDa polypeptide. A galectin functions as a linker of the AF to the cell-membrane-associated receptor, the aggregation receptor (AR). The most important extracellular matrix molecules are collagen- and fibronectin-like molecules. These proteins interact with the cell-membrane receptors, the integrins. In addition, a neuronal receptor has been identified, which--together with the identified neuroactive molecules--indicate the existence of a primordial neuronal network already in Porifera. The primmorph system, aggregated cells that retain the capacity to proliferate and differentiate, has been used to demonstrate that a homeobox-containing gene, Iroquois, is expressed during canal formation in primmorphs. The formation of a body plan in sponges is supported by skeletal elements, the spicules, which are composed in Demospongiae as well as in Hexactinellida of amorphous, noncrystalline silica. In Demospongiae the spicule formation is under enzymic control of silicatein. Already at least one morphogen has been identified in sponges, myotrophin, which is likely to be involved in the axis formation. Taken together, these elements support the recent conclusions that sponges are not merely nonorganized cell aggregates, but already complex animals provided with a defined body plan.

The Chemokine Networks in Sponges: Potential Roles in Morphogenesis, Immunity and Stem Cell Formation

Porifera (sponges) are now well accepted as the phylum which branched off first from the common ancestor of all metazoans, the Urmetazoa. The transition to the Metazoa became possible because during this phase, cell-cell as well as cell-matrix adhesion molecules evolved which allowed the formation of a colonial stage of animals. The next prerequisite for the evolution to the Urmetazoa was the establishment of an effective immune system which, flanked by apoptosis, allowed the formation of a first level of individuation. In sponges (with the model Suberites domuncula and Geodia cydonium), the main mediators of the immune responses are the chemokines. Since sponges lack a vascular system and consequently blood cells (in the narrow sense), we have used the term chemokines (in a broad sense) to highlight that the complex network of intercellular mediators initiates besides differentiation processes also cell movement. In the present review, the cDNAs encoding the following chemokines were described and the roles of their deduced proteins during self-self and nonself recognition outlined: the allograft inflammatory factor, the glutathione peroxidase, the endothelial-monocyte-activating polypeptide, the pre-B-cell colony-enhancing factor and the myotrophin as well as an enzyme, the (2-5)A synthetase, which is involved in cytokine response in vertebrates. A further step required to reach the evolutionary step of the integrated stage of the Urmetazoa was the acquisition of a stem cell system. In this review, first markers for stem cells (mesenchymal stem cell-like protein) as well as for chemokines involved in the maintenance of stem cells (noggin and glia maturation factor) are described at the molecular level, and a first functional analysis is approached. Taken together, it is outlined that the chemokine network was essential for the establishment of metazoans, which evolved approximately 600 to 800 million years ago.

Induction of (2'-5')oligoadenylate synthetase in the marine sponges Suberites domuncula and Geodia cydonium by the bacterial endotoxin lipopolysaccharide

Recent studies have shown that the Porifera, with the examples of the demosponges Suberites domuncula and Geodia cydonium, comprise a series of pathways found also in the immune system of Deuterostomia, such as vertebrates, but are absent in Protostomia, with insects or nematodes as examples. One pathway is the (2'-5')oligoadenylate synthetase [(2-5)A synthetase] system. In the present study we show that crude extracts from tissue of S. domuncula collected from the sea display a considerable amount of (2-5)A synthetase activity; 16% of the ATP substrate is converted to the (2-5)A product, while tissue from specimens which were kept for 6 months in an aquarium shows only 1% of conversion. As aquarium animals show a lower bacterial load, those specimens were treated for the experiments with the bacterial endotoxin lipopolysaccharide (LPS); they responded to LPS with a stimulation of the (2-5)A synthetase activity. To monitor if this effect can be obtained also on the in vitro level, primmorphs which comprise proliferating and differentiating cells, were incubated with LPS. Extracts obtained from LPS-treated primmorphs also convert ATP to the (2-5)A products mediated by the synthetase. In parallel to this effect on protein level, LPS causes after an incubation period of 12 h also an increase in the steady-state level of the transcripts encoding the putative (2-5)A synthetase. It is postulated that in sponges the (2-5)A synthetase is involved in antimicrobial defense of the animals.

Sponge Bcl-2 homologous protein (BHP2-GC) confers distinct stress resistance to human HEK-293 cells

It is established that sponges, the phylogenetically oldest still extant phylum of Metazoa, possess key molecules of the apoptotic pathways, that is members from the Bcl-2 family and a pro-apoptotic molecule with death domains. Here we report on transfection studies of human cells with a sponge gene, GCBHP2. Sponge tissue was exposed to heat shock and tributyltin, which caused an upregulation of gene expression of GCBHP2. The cDNA GCBHP2 was introduced into human HEK-293 cells and mouse NIH-3T3 cells; the stable transfection was confirmed by the identification of the transcripts, by Western blotting as well as by immunofluorescence using antibodies raised against the recombinant polypeptide. HEK-293 cells, transfected with GCBHP2, showed high resistance to serum starvation and tributyltin treatment, compared to mock-transfected cells. In contrast to mock-transfected cells, GCBHP2-transfected cells activated caspase-3 to a lower extent. Thus, sponges contain gene(s) involved in apoptotic pathway(s) displaying their function also in human cells.

Suppression of allograft rejection in the sponge Suberites domuncula by FK506 and expression of genes encoding FK506-binding proteins in allografts

Porifera (sponges) are, evolutionarily, the oldest metazoan phylum. Recent molecular data suggest that these animals possess molecules similar to and homologous with those of the innate and adaptive immune systems of higher Metazoa. Applying the biological system of parabiosis and the technique of differential display of mRNA, two cDNAs encoding putative FK506-binding proteins were isolated. FK506 is successfully used in clinics as a drug to prevent allograft rejection and is toxic to Suberites domuncula cells in vitro at doses above 100ng ml−1. Autograft fusion of transplants from S. domuncula was not affected by FK506. Allograft non-fusion was not affected by FK506 at toxic doses; however, at the non-toxic dose of 20ng ml−1, the allografts fused with each other. It is shown that at the attachment zone in untreated and (particularly drastic) in FK506-treated allografts, expression of the genes encoding the FK506-binding proteins is upregulated. These data indicate that the drug FK506 suppresses allograft rejection in S. domuncula, most probably via interaction with expression of the gene coding for the FK506-binding proteins.

Review: How was metazoan threshold crossed? The hypothetical Urmetazoa

The origin of Metazoa remained--until recently--the most enigmatic of all phylogenetic problems. Sponges [Porifera] as "living fossils", positioned at the base of multicellular animals, have been used to answer basic questions in metazoan evolution by molecular biological techniques. During the last few years, cDNAs/genes coding for informative proteins have been isolated and characterized from sponges, especially from the marine demosponges Suberites domuncula and Geodia cydonium. The analyses of their deduced amino acid sequences allowed a molecular biological resolution of the monophyly of Metazoa. Molecules of the extracellular matrix/basal lamina, with the integrin receptor, fibronectin and galectin as prominent examples, cell-surface receptors (tyrosine kinase receptors), elements of nerve system/sensory cells (metabotropic glutamate receptor), homologs/modules of an immune system [immunoglobulin-like molecules, SRCR- and SCR-repeats, cytokines, (2-5)A synthetase], as well as morphogens (myotrophin) classify the Porifera as true Metazoa. As "living fossils", provided with simple, primordial molecules allowing cell-cell and cell-matrix adhesion, as well as processes of signal transduction as known in a more complex manner from higher Metazoa, sponges also show peculiarities. Tissues of sponges are rich in telomerase activity, suggesting a high plasticity in the determination of cell lineages. It is concluded that molecular biological studies with sponges as models will not only help to understand the evolution to the Metazoa but also the complex, hierarchical regulatory network of cells in higher Metazoa [reviewed in Progress in Molecular Subcellular Biology, vols. 19, 21 (1998) Springer Verlag]. The hypothetical ancestral animal, the Urmetazoa, from which the metazoan lineages diverged (more than 600 MYA), may have had the following characteristics: cell adhesion molecules with intracellular signal transduction pathways, morphogens/growth factors forming gradients, a functional immune system, and a primordial nerve cell/receptor system.

Stimulation of protein (collagen) synthesis in sponge cells by a cardiac myotrophin-related molecule from Suberites domuncula

The body wall of sponges (Porifera), the lowest metazoan phylum, is formed by two epithelial cell layers of exopinacocytes and endopinacocytes, both of which are associated with collagen fibrils. Here we show that a myotrophin-like polypeptide from the sponge Suberites domuncula causes the expression of collagen in cells from the same sponge in vitro. The cDNA of the sponge myotrophin was isolated; the potential open reading frame of 360 nt encodes a 120 aa long protein (Mr of 12,837). The sequence SUBDOMYOL shares high similarity with the known metazoan myotrophin sequences. The expression of SUBDOMYOL is low in single cells but high after formation of primmorph aggregates as well as in intact animals. Recombinant myotrophin was found to stimulate protein synthesis by fivefold, as analyzed by incorporation studies using [3H] lysine. In addition, it is shown that after incubation of single cells with myotrophin, the primmorphs show an unusual elongated, oval-shaped appearance. It is demonstrated that in the presence of recombinant myotrophin, the cells up-regulate the expression of the collagen gene. The cDNA for S. domuncula collagen was isolated; the deduced aa sequence shows that the collagenous internal domain is rather short, with only 24 G-x-y collagen triplets. We conclude that the sponge myotrophin causes in homologous cells the same/similar effect as the cardiac myotrophin in mammalian cells, where it is involved in initiation of cardial ventricular hypertrophy. We assume that an understanding of sponge molecular cell biology will also contribute to a further elucidation of human diseases, here of the cardiovascular system.