Identification and isolation of a retrotransposon from the freshwater sponge Lubomirskia baicalensis: implication in rapid evolution of endemic sponges.

Transposons are mobile genetic elements that are found in all major branches of life. Similarities to retroviruses concerning genome structure and transposition mechanism suggest a familial relationship. Transposons are important evolutionary drivers that trigger genetic changes such as genomic rearrangement, alteration of gene expression, and gene duplication. And, indeed, now more than ever the effect of transposons on genome evolution represents a dynamic field of research. Since sponges (phylum Porifera) are the phylogenetically oldest still extant metazoan taxon, the study of poriferan mobile elements contributes to the understanding of the generation of phenotypic diversity and speciation at the base of the metazoan tree of life. This work describes the analyses of the first poriferan mobile genetic element so far identified, the long terminal repeats- retrotransposon Baikalum-1 of Lubomirskia baicalensis (Demospongiae; Ceractinomorpha). Baikalum-1 embraces a continuous open reading frame, putatively coding for a polyprotein that consists of nucleo capsid, protease, reverse transcriptase, RNase H, and integrase, all proteins/ enzymes characteristic of retrotransposons. Baikalum-1 was discovered in all freshwater sponge species endemic to Lake Baikal, as well as in cosmopolitan sponge species that inhabit a Lake Baikal-feeding rivulet. However, the same cosmopolitan species sampled from lakes and rivers (Siberian and European) with no direct contact to Lake Baikal did not contain this particular mobile genetic element. Thus, Baikalum-1 is probably the result of an evolutionarily ancient retroviral infection that spread exclusively amongst Baikalian sponge species. In addition, the retro-transposon is found in the vicinity of the silicatein-A1 gene. Silicateins are cathepsin-like proteins that catalyze the synthesis of poriferan siliceous skeletal elements (spicules). In L. baicalensis, the silicatein-A1 gene is flanked by two palindroms, probably remnants of transposons that might be responsible for the emergence of four different silicatein genes, uniquely present in freshwater but not marine sponges. Adaptation of sponges to the freshwater habitat (with its significantly higher silica content compared to the marine milieu) required the ability to evolve rapidly, which could be conferred by high transpositional activity, accompanied by duplication and diversification of the ancestral silicatein gene of marine species.

Analysis of the axial filament in spicules of the demosponge Geodia cydonium: different silicatein composition in microscleres (asters) and megascleres (oxeas and triaenes).

The skeleton of the siliceous sponges (Porifera: Hexactinellida and Demospongiae) is supported by spicules composed of bio-silica. In the axial canals of megascleres, harboring the axial filaments, three isoforms of the enzyme silicatein (-alpha, -beta and -gamma) have been identified until now, using the demosponges Tethya aurantium and Suberites domuncula. Here we describe the composition of the proteinaceous components of the axial filament from small spicules, the microscleres, in the demosponge Geodia cydonium that possesses megascleres and microscleres. The morphology of the different spicule types is described. Also in G. cydonium the synthesis of the spicules starts intracellularly and they are subsequently extruded to the extracellular space. In contrast to the composition of the silicateins in the megascleres (isoforms: -alpha, -beta and -gamma), the axial filaments of the microscleres contain only one form of silicatein, termed silicatein-alpha/beta, with a size of 25kDa. Silicatein-alpha/beta undergoes three phosphorylation steps. The gene encoding silicatein-alpha/beta was identified and found to comprise the same characteristic sites, described previously for silicateins-alpha or -beta. It is hypothesized, that the different composition of the axial filaments, with respect to silicateins, contributes to the morphology of the different types of spicules.

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.

Co-expression and functional interaction of silicatein with galectin: matrix-guided formation of siliceous spicules in the marine demosponge Suberites domuncula.

Sponges (phylum Porifera) of the class of Demospongiae are stabilized by a siliceous skeleton. It is composed of silica needles (spicules), which provide the morphogenetic scaffold of these metazoans. In the center of the spicules there is an axial filament that consists predominantly of silicatein, an enzyme that catalyzes the synthesis of biosilica. By differential display of transcripts we identified additional proteins involved in silica formation. Two genes were isolated from the marine demosponge Suberites domuncula; one codes for a galectin and the other for a fibrillar collagen. The galectin forms aggregates to which silicatein molecules bind. The extent of the silicatein-mediated silica formation strongly increased if associated with the galectin. By applying a new and mild extraction procedure that avoids hydrogen fluoride treatment, native axial filaments were extracted from spicules of S. domuncula. These filaments contained, in addition to silicatein, the galectin and a few other proteins. Immunogold electron microscopic studies underscored the role of these additional proteins, in particular that of galectin, in spiculogenesis. Galectin, in addition to silicatein, presumably forms in the axial canal as well as on the surface of the spicules an organized net-like matrix. In the extraspicular space most of these complexes are arranged concentrically around the spicules. Taken together, these additional proteins, working together with silicatein, may also be relevant for potential (nano)-biotechnological applications of silicatein in the formation of surface coatings. Finally, we propose a scheme that outlines the matrix (galectin/silicatein)-guided appositional growth of spicules through centripetal and centrifugal synthesis and deposition of biosilica.

Novel mechanism for the radiation-induced bystander effect: nitric oxide and ethylene determine the response in sponge cells.

Until now the bystander effect had only been described in vertebrates. In the present study the existence of this effect has been demonstrated for the phylogenetically oldest metazoan phylum, the Porifera. We used the demosponge Suberites domuncula for the experiments in the two-chamber-system. The lower dish contained irradiated "donor" cells (single cells) and the upper dish the primmorphs ("recipient" primmorphs). The "donor" cells were treated with UV-B light (40 mJ/cm2) and 100 microM hydrogen peroxide (H2O2), factors that exist also in the natural marine aquatic environment of sponges; these factors caused a high level of DNA strand breaks followed by a reduced viability of the cells. If these cells were added to the "recipient" primmorphs these 3D-cell cultures started to undergo apoptosis. This effect could be abolished by the NO-specific scavenger PTIO and ethylene. The conclusion that NO is synthesized by the UV-B/H2O2-treated cells was supported analytically. The cDNA encoding the enzyme dimethylarginine dimethylaminohydrolase (DDAH) was isolated from the "donor" cells. High levels of DDAH transcripts were measured in UV-B/H2O2-treated "donor" cells while after ethylene treatment the steady-state level of expression drops drastically. We conclude that in the absence of ethylene the concentration of the physiological inhibitor for the NO synthase ADMA is low, due to the high level of DDAH. In consequence, high amounts of NO are released from "donor" cells which cause apoptosis in "recipient" primmorphs. In contrast, ethylene reduces the DDAH expression with the consequence of higher levels of ADMA which prevent the formation of larger amounts of NO. This study describes the radiation-induced bystander effect also for the most basal metazoans and demonstrates that this effect is controlled by the two gases NO and ethylene.

Expression of silicatein in spicules from the Baikalian sponge Lubomirskia baicalensis.

Lake Baikal harbors the largest diversity of sponge species [phylum Porifera] among all freshwater biotopes. The abundantly occurring species Lubomirskia baicalensis was used to study the seasonal silicatein metabolism; the spicules of this species have an unusually thick axial filament, consisting of silicatein, which remains constant in diameter during their growth. In the course of maturation, the size of the silicic acid shell grows, until the final diameter of the spicules of about 8 microm is reached. The seasonal content of silicatein was assessed by use of antibodies raised against silicatein; they stained specifically the axial filaments. In addition we determined, by application of the enzyme-linked immunosorbent assay system, that the proteinaceous content of the spicules, the silicatein, increases from spring to late summer by 8-fold. As molecular markers to quantify the seasonal changes in expression levels of genes coding for proteins/enzymes, the genes for the calumenin-like protein and the kinesin-related protein, were selected. The expression of calumenin-like gene, involved in the intracellular signaling, is highest during September, whereas the expression of the kinesin-related protein does not change during the annual course. These results suggest that the highest metabolic activity of L. baicalensis occurs in late summer (September), in parallel with the highest accumulation of silicatein, a structural protein/enzyme of the spicules.

Selenium affects biosilica formation in the demosponge Suberites domuncula. Effect on gene expression and spicule formation.

Selenium is a trace element found in freshwater and the marine environment. We show that it plays a major role in spicule formation in the demosponge Suberites domuncula. If added to primmorphs, an in vitro sponge cell culture system, it stimulates the formation of siliceous spicules. Using differential display of transcripts, we demonstrate that, after a 72-h exposure of primmorphs to selenium, two genes are up-regulated; one codes for selenoprotein M and the other for a novel spicule-associated protein. The deduced protein sequence of selenoprotein M (14 kDa) shows characteristic features of metazoan selenoproteins. The spicule-associated protein (26 kDa) comprises six characteristic repeats of 20 amino acids, composed of 10 distinct hydrophobic regions ( approximately 9 amino acids in length). Recombinant proteins were prepared, and antibodies were raised against these two proteins. Both were found to stain the central axial filament, which comprises the silicatein, as well as the surface of the spicules. In the presence of selenium, only the genes for selenoprotein M and spicule-associated protein are up-regulated, whereas the expression of the silicatein gene remains unchanged. Finally we show that, in the presence of selenium, larger silica aggregates are formed. We conclude that selenium has a stimulatory effect on the formation of siliceous spicules in sponges, and it may be involved in the enzymatic synthesis of biosilica components.

Innate immune defense of the sponge Suberites domuncula against bacteria involves a MyD88-dependent signaling pathway. Induction of a perforin-like molecule.

Sponges (phylum Porifera) are the phylogenetically oldest metazoa; as filter feeders, they are abundantly exposed to marine microorganisms. Here we present data indicating that the demosponge Suberites domuncula is provided with a recognition system for gram-negative bacteria. The lipopolysaccharide (LPS)-interacting protein was identified as a receptor on the sponge cell surface, which recognizes the bacterial endotoxin LPS. The cDNA was isolated, and the protein (Mr 49,937) was expressed. During binding to LPS, the protein dimerizes and interacts with MyD88, which was also identified and cloned. The sponge MyD88 (Mr 28,441) is composed of two protein interaction domains, a Toll/interleukin-1 receptor domain (found in MyD88 and in Toll-like receptors) and a death domain (present in MyD88 and interleukin-1 receptor-associated kinase). Northern blot experiments and in situ hybridization studies showed that after LPS treatment, the level of the LPS-interacting protein remains unchanged, whereas MyD88 is strongly up-regulated. A perforin-like molecule (Mr 74,171), the macrophage-expressed protein, was identified as an executing molecule of this pathway. This gene is highly expressed after LPS treatment, especially at the surfaces of the animals. The recombinant protein possesses biological activity and eliminates gram-negative bacteria; it is inactive against gram-positive bacteria. These data indicate that S. domuncula is provided with an innate immune system against gram-negative bacteria; the ligand LPS (a pathogen-associated molecular pattern) is recognized by the pattern recognition receptor (LPS-interacting protein), which interacts with MyD88. A signal transduction is established, which results in an elevated expression of MyD88 as well as of the macrophage-expressed protein as an executing protein.

Biosilica formation in spicules of the sponge Suberites domuncula: synchronous expression of a gene cluster.

The formation of spicules is a complicated morphogenetic process in sponges (phylum Porifera). The primmorph system was used to demonstrate that in the demosponge Suberites domuncula the synthesis of the siliceous spicules starts intracellularly and is dependent on the concentration of silicic acid. To understand spicule formation, a cluster of genes was isolated. In the center of this cluster is the silicatein gene, which codes for the enzyme that synthesizes spicules. This gene is flanked by an ankyrin repeat gene at one side and by a tumor necrosis factor receptor-associated factor and a protein kinase gene at the other side. All genes are strongly expressed in primmorphs and intact animals after exposure to silicic acid, and this expression is restricted to those areas where the spicule formation starts or where spicules are maintained in the animals. Our observations suggest that in S. domuncula a coordinated expression of physically linked genes is essential for the synthesis of the major skeletal elements.

Arginine kinase in the demosponge Suberites domuncula: regulation of its expression and catalytic activity by silicic acid.

In Demospongiae (phylum Porifera) the formation of the siliceous skeleton, composed of spicules, is an energetically expensive reaction. The present study demonstrates that primmorphs from the demosponge Suberites domuncula express the gene for arginine kinase after exposure to exogenous silicic acid. The deduced sponge arginine kinase sequence displays the two characteristic domains of the ATP:guanido phosphotransferases; it can be grouped to the 'usual' mono-domain 40 kDa guanidino kinases (arginine kinases). Phylogenetic studies indicate that the metazoan guanidino kinases evolved from this ancestral sponge enzyme; among them are also the 'unusual' two-domain 80 kDa guanidino kinases. The high expression level of the arginine kinase gene was already measurable 1 day after addition of silicic acid by northern blot, as well as by in situ hybridization analysis. Parallel determinations of enzyme activity confirmed that high levels of arginine kinase are present in primmorphs that had been exposed for 1-5 days to silicic acid. Finally, transmission electron-microscopical studies showed that primmorphs containing high levels of arginine kinase also produce siliceous spicules. These data highlight that silicic acid is an inorganic morphogenetic factor that induces the expression of the arginine kinase, which in turn probably catalyzes the reversible transfer of high-energy phosphoryl groups.

Dynamics of skeleton formation in the Lake Baikal sponge Lubomirskia baicalensis. Part II. Molecular biological studies.

In a preceding study it has been reported that the freshwater sponge Lubomirskia baicalensis, living in Lake Baikal (East Siberia), is composed of spicules forming a characteristic pattern which follows radiate accretive growth. Here we report that the spicules are synthesized by the enzyme silicatein, a protein which is related to cathepsin L. The cDNAs for silicatein and the related cathepsin L were isolated and used as probes to show that the mRNA levels of silicatein in the bases of the spicule skeleton of the animals are low, while the mRNA level of cathepsin L in this region exceeds that of the growing zone. This is the first comprehensive study on the importance of the axial filament/silicatein as an essential structural and functional component determining the growth and stability of demosponge spicules.

Dynamics of skeleton formation in the Lake Baikal sponge Lubomirskia baicalensis. Part I. Biological and biochemical studies.

In ancient Lake Baikal (East Siberia), freshwater sponges have diversified to an extraordinary degree. The skeleton of Lubomirskia baicalensis, which attains a size of up to 1 m, is constructed from spicules, which are cemented into longitudinal bundles. Our X-ray analysis revealed that the architecture of the specimens follows a highly ordered radiate accretive growth pattern. The spicules have a central axial canal with an axial filament inside. This organic filament is composed of silicatein, the major enzyme involved in silica formation of the spicules. We found that the specific activity of silicatein in samples from the non-growing (basal) zone is much lower than in those from the growth zone (tips) and that even the composition of this molecule differs in these regions. The present study shows for the first time that the turnover of silicatein, the major element of the axial canal of sponge spicules, changes within a sponge specimen depending on the region in which it is found.

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.

Porifera a reference phylum for evolution and bioprospecting: the power of marine genomics.

The term Urmetazoa, as the hypothetical metazoan ancestor, was introduced to highlight the finding that all metazoan phyla including the Porifera [sponges] derived from one common ancestor. Analyses of sponge genomes, from Demospongiae, Calcarea and Hexactinellida have permitted the reconstruction of the evolutionary trail from Fungi to Metazoa. This has provided evidence that the characteristic evolutionary novelties of Metazoa existing in Porifera share high sequence similarities and in some aspects also functional similarities to related polypeptides found in other metazoan phyla. It is surprising that the genome of Porifera is large and comprises substantially more genes than Protostomia and Deuterostomia. On the basis of solid taxonomy and ecological data, the high value of this phylum for human application becomes obvious especially with regard to the field of chemical ecology and the hope to find novel potential drugs for clinical use. In addition, the benefit of efforts in understanding molecular biodiversity with focus on sponges can be seen in the fact that these animals as "living fossils" allow to stethoscope into the past of our globe especially with respect to the evolution of Metazoa.

Traditional and Modern Biomedical Prospecting: Part II-the Benefits: Approaches for a Sustainable Exploitation of Biodiversity (Secondary Metabolites and Biomaterials from Sponges).

The progress in molecular and cell biology has enabled a rational exploitation of the natural resources of the secondary metabolites and biomaterials from sponges (phylum Porifera). It could be established that these natural substances are superior for biomedical application to those obtained by the traditional combinatorial chemical approach. It is now established that the basic structural and functional elements are highly conserved from sponges to the crown taxa within the Protostomia (Drosophila melanogaster and Caenorhabditis elegans) and Deuterostomia (human); therefore, it is obvious that the molecular etiology of diseases within the metazoan animals have a common basis. Hence, the major challenge for scientists studying natural product chemistry is to elucidate the target(s) of a given secondary metabolite, which is per se highly active and selective. After this step, the potential clinical application can be approached. The potential value of some selected secondary metabolites, all obtained from sponges and their associated microorganisms, is highlighted. Examples of compounds that are already in medical use (inhibition of tumor/virus growth [arabinofuranosyl cytosine and arabinofuranosyl adenine]), or are being considered as lead structures (acting as cytostatic and anti-inflammatory secondary metabolites [avarol/avarone], causing induction of apoptosis [sorbicillactone]) or as prototypes for the interference with metabolic pathways common in organisms ranging from sponges to humans (modulation of pathways activated by fungal components [aeroplysinin], inhibition of angiogenesis [2-methylthio-1,4-napthoquinone], immune modulating activity [FK506]) are discussed in this study. In addition, bioactive proteins from sponges are listed (antibacterial activity [pore-forming protein and tachylectin]). Finally, it is outlined that the skeletal elements-the spicules-serve as blueprints for new biomaterials, especially those based on biosilica, which might be applied in biomedicine. These compounds and biomaterials have been isolated/studied by members of the German Center of Excellence BIOTECmarin. The goal for the future is to successfully introduce some of these compounds in the treatment of human diseases in order to raise the public awareness on the richness and diversity of natural products, which should be sustainably exploited for human benefit.

Evolution of metazoan cell junction proteins: the scaffold protein MAGI and the transmembrane receptor tetraspanin in the demosponge Suberites domuncula.

Until recently the positioning of the sponges (phylum Porifera) within the metazoan systematics was hampered by the lack of molecular evidence for the existence of junctional structures in the surface cell layers. In this study two genes related to the tight junctions are characterized from the demosponge Suberites domuncula: tetraspanin (SDTM4SF), a cell surface receptor, and MAGI (SDMAGI), a MAGUK (membrane-associated guanylate kinase homologue) protein. Especially the MAGI protein is known in other metazoan animal phyla to exist exclusively in tight junctions. The characteristic domains of MAGI proteins (six PDZ domains, two WW domains, and a truncated guanylate kinase motif) are conserved in the sponge protein. The functional analysis of SDMAGI done by in situ hybridization shows its expression in the surface epithelial layers (exopinacoderm and endopinacoderm). Northern blot studies reveal that expression of SDMAGI and SDTM4SF increases after formation of the pinacoderm layer in the animals as well as in primmorphs. These results support earlier notions that sponges contain junctional structures. We conclude that sponges contain epithelia whose cells are organized by cell junctions.

Molecular markers for germ cell differentiation in the demosponge Suberites domuncula.

Sponges (phylum Porifera) are simple metazoans for which no molecular information on gametogenesis and larval development is available. To support the current study, it was confirmed by histology that oocytes and larvae were produced by the demosponge Suberites domuncula. Three genes/expressed products from S. domuncula whose expression correlated with sexual reproduction were identified and characterized (they are used here as marker genes): i) a receptor tyrosine kinase (RTK) with sequence similarity in the tyrosine kinase domain to fibroblast growth factor receptors; ii) the sex-determining protein FEM1 and iii) the sperm associated antigen (SAA) of triploblasts. Antibodies against the extracellular domain of the RTK specifically stained oocytes and larvae in S. domuncula tissue sections. Induction of these three genes was successful at elevated temperature, a factor which also promotes natural gametogenesis. In situ hybridization analyses revealed that FEM1 and SAA were expressed in those areas in which gametogenesis begins. Our results indicate that genes which play a role in sex determination may be present in Porifera.

Traditional and Modern Biomedical Prospecting: Part I-the History: Sustainable Exploitation of Biodiversity (Sponges and Invertebrates) in the Adriatic Sea in Rovinj (Croatia).

Nature, especially the marine environment, provides the most effective drugs used in human therapy. Among the metazoans, the marine sponges (phylum Porifera), which are sessile filter feeders, produce the most potent and highly selective bioactive secondary metabolites. These animals (or their associated symbiotic microorganisms) synthesize secondary metabolites whose activity and selectivity has developed during their long evolutionary history (evochemistry). The exploitation of these resources has become possible due to the progress in molecular and cell biology. BIOTECmarin, the German Center of Excellence follows this rationale. In the past, these animals have been successfully and extensively utilized to isolate bioactive compounds and biomaterials for human benefit. Pharmaceuticals prepared from marine animals, primarily sponges, have been applied since ancient times (Hippocrates, Aristotle and later Plinius). It has been reported that extracts and/or components from sponges can be used for the treatment of specific diseases. For a systematic and applied-oriented exploitation, the successful development of effective compounds largely depends on quality of the institutional infrastructure of marine stations and more so on the biodiversity. The Center for Marine Research in Rovinj (Croatia) fulfils these prerequisites. Founded in 1891, this institute has to its credit major discoveries related to exploitation of secondary metabolites/biomaterials from sponges for therapeutical application and to obtain biomaterials for general wellbeing. This is the first part of a review focusing on biomedical prospecting. Here, we have mainly described the historic background. The details of techniques, substances, approaches and outlooks will be discussed in the second part.

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.