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PubMed2006

Cnidarian chemical neurotransmission, an updated overview.

The ultrastructural, histochemical, immunocytochemical, biochemical, molecular, behavioral and physiological evidence for non-peptidergic and peptidergic chemical neurotransmission in the Anthozoa, Hydrozoa, Scyphozoa and Cubozoa is surveyed. With the possible exception of data for the catecholamines and peptides in some animals, the set of cumulative data - the evidence from all methodologies - is incomplete. Taken together, the evidence from all experimental approaches suggests that both classical fast (acetylcholine, glutamate, GABA, glycine) and slow (catecholamines and serotonin) transmitters, as well as neuropeptides, are involved in cnidarian neurotransmission. Ultrastructural evidence for peptidergic, serotonergic, and catecholaminergic synaptic localization is available, but the presence of clear and dense-cored synaptic vesicles also suggests both fast and slow classical transmission. Immunocytochemical studies, in general, reveal a continuous, non-localized distribution of neuropeptides, suggesting a neuromodulatory role for them. Immunocytochemical and biochemical studies indicate the presence of glutamate, GABA, serotonin, catecholamines (and/or their receptors), RFamides, nitric oxide and eicosanoids in cnidarian neurons and tissues. Gene sequences for peptidergic preprohormones have been reported; putative gene homologies to receptor proteins for vertebrate transmitters have been found in Hydra. Behavioral and physiological studies implicate classical transmitters, neuropeptides, eicosanoids and nitric oxide in the coordination of the neuroeffector systems.

Animals↗
PubMed2004

Phospholipase A2 in cnidaria.

Phospholipase A2 (PLA2) is an enzyme present in snake and other venoms and body fluids. We measured PLA2 catalytic activity in tissue homogenates of 22 species representing the classes Anthozoa, Hydrozoa, Scyphozoa and Cubozoa of the phylum Cnidaria. High PLA2 levels were found in the hydrozoan fire coral Millepora sp. (median 735 U/g protein) and the stony coral Pocillopora damicornis (693 U/g) that cause skin irritation upon contact. High levels of PLA2 activity were also found in the acontia of the sea anemone Adamsia carciniopados (293 U/g). Acontia are long threads containing nematocysts and are used in defense and aggression by the animal. Tentacles of scyphozoan and cubozoan species had high PLA2 activity levels: those of the multitentacled box jellyfish Chironex fleckeri contained 184 U/g PLA2 activity. The functions of cnidarian PLA2 may include roles in the capture and digestion of prey and defense of the animal. The current observations support the idea that cnidarian PLA2 may participate in the sting site irritation and systemic envenomation syndrome resulting from contact with cnidarians.

Animals↗
PubMed2004

Cloning of anthozoan fluorescent protein genes.

Many cnidarians display vivid fluorescence under proper lighting conditions. In general, these colors are due to the presence of fluorescent proteins similar to the green fluorescent protein (GFP) originally isolated from the hydrozoan medusa Aequorea victoria (Cnidaria: Hydrozoa). To optimize the search for new fluorescent proteins (FPs), a technique was developed that allows for the rapid cloning and screening of FP genes without the need for a prior knowledge of gene sequence. Using this method, four new FP genes were cloned, a green from Montastraea cavernosa (Anthozoa: Scleractinia: Faviidae), a cyan from Pocillopora damicornis (Anthozoa: Scleractinia: Pocilloporidae), a cyan from Discosoma striata (Anthozoa: Corallimorpharia), and a red from a second Discosoma species. Two additional green FPs were cloned, one from M. cavernosa and one from its congener Montastraea faveolata, from purified cDNA using PCR primers designed for the first M. cavernosa green FP. Each FP has recognizable amino acid sequence motifs that place them conclusively in the GFP protein family. Mutation of these products using a low-stringency PCR protocol followed by screening of large numbers of bacterial colonies allowed rapid creation of mutants with a variety of characteristics, including changes in color, maturation time, and brightness. An enhanced version of the new red FP, DspR1+, matures faster at 30 degrees C than the commercially available DsRed but matures slower than DsRed at 37 degrees C. One of the M. cavernosa green FPs, McaG2, is highly resistant to photobleaching and has a fluorescence quantum yield approximately twice that of EGFP-1.

Amino Acid Sequence↗
PubMed2005

Mesogleal cells of the jellyfish Aurelia aurita are involved in the formation of mesogleal fibres.

The extracellular matrix of the jellyfish Aurelia aurita (Scyphozoa, Cnidaria), known as the mesoglea, is populated by numerous mesogleal cells (Mc). We determined the pattern of the Mc and the mesoglea, raised polyclonal antibodies (RA47) against the major mesogleal protein pA47 (47 kDa) and checked their specificity. In the mesoglea, RA47 stains pA47 itself. In immunoblots of Mc, RA47 stains bands of 120 kDa and 80 kDa; weaker staining is observed at pA47. The same staining pattern is seen on blots of jellyfish epidermal cells and of whole Hydra (Hydrozoa) or isolated mesoglea of Hydra. Our data indicate that pA47 is synthesized by Mc and epidermal cells as high molecular precursors. Using immunostaining techniques, we showed Mc to be involved in the formation of mesogleal non-collagenous (called "elastic" in classic morphological studies) fibres. The biochemical and morphological data suggest that Mc originate from the epidermis.

Animals↗
PubMed2005

Fluorescent proteins as a toolkit for in vivo imaging.

Green fluorescent protein (GFP) from the jellyfish Aequorea victoria, and its mutant variants, are the only fully genetically encoded fluorescent probes available and they have proved to be excellent tools for labeling living specimens. Since 1999, numerous GFP homologues have been discovered in Anthozoa, Hydrozoa and Copepoda species, demonstrating the broad evolutionary and spectral diversity of this protein family. Mutagenic studies gave rise to diversified and optimized variants of fluorescent proteins, which have never been encountered in nature. This article gives an overview of the GFP-like proteins developed to date and their most common applications to study living specimens using fluorescence microscopy.

Biosensing Techniques↗
PubMed2006

Molecular phylogenetics in Hydra, a classical model in evolutionary developmental biology.

Among the earliest diverging animal phyla are the Cnidaria. Freshwater polyps of the genus Hydra (Cnidaria, Hydrozoa) have long been of general interest because different species of Hydra reveal fundamental principles that underlie development, differentiation, regeneration and also symbiosis. The phylogenetic relationships among the Hydra species most commonly used in current research are not resolved yet. Here we estimate the phylogenetic relations among eight scientifically important members of the genus Hydra with molecular data from two nuclear (18S rDNA, 28S rDNA) and two mitochondrial (16S rRNA, cytochrome oxidase subunit I (COI)) genes. The phylogenetic trees obtained by maximum parsimony (MP), maximum likelihood (ML) and Bayesian inference (BI) methods were generally compatible with present morphological classification patterns. However, the present analysis also bears on several long-standing questions about Hydra systematics and reveals some characteristics of the phylogenetic relationships of this genus that were unknown so far. It indicates that Hydra viridissima, the only species in Hydra, which contains symbiotic algae, might be considered as the sister group to all other species within this genus. Analyses of both nuclear and mitochondrial sequences support the view that Hydra oligactis and Hydra circumcincta are sisters to all other Hydra species. Unexpectedly, we also find that in contrast to its initial description, the strain used for making transgenic Hydra, Hydra vulgaris (strain AEP) is more closely related to Hydra carnea than to other species of Hydra.

Animals↗
PubMed1987

Model of pattern formation in epithelial morphogenesis.

One of the most universal events in morphogenesis is the formation of domains of morphologically polarized cells in the initially homogeneous epithelial sheets. We investigate the possibility of considering this process as a phenomenon of self-organization which is based upon the following experimentally proven mechanochemical cell properties: (1) a capacity of individual cells for morphological polarization considered as a bistable "all-or-none" transition of a cell from a non-polarized to a polarized state; (2) transmission of this capacity from one cell to another on their contacts; (3) feedback relations between co-operative cell polarization and tangential elastic tensions in a cell sheet: cell polarization increases tangential tensions whereas the latter inhibit further cell polarization. We have constructed a phenomenological model which formally expresses the above properties. Its mathematical description includes but few macroscopic parameters available to experimental investigation and controlled changes. The analysis of the collective dynamic regimes of cell polarization demonstrates that variations of some non-specific parameters leads to spontaneous transition in the morphology of cell layers accompanied by symmetry breaking (Turing's instability). Under these conditions either long-range ordered patterns of cell polarization (including hexagonal cell nets) or non-regular spotted structures can emerge. In the particular case of a sheet having fixed complete dimensions and lacking any external elastic bonds a stable macrostate is created; it corresponds to the sheet's binary subdivision into polarized and non-polarized cell domains of size-invariant proportions. The model conclusions are compared with the morphogenetical processes in sea-urchin development, the morphogenesis of skin derivates and artificially induced budding in hydrozoa.

Animals↗
PubMed2001

Putative glycine receptors in Hydra: a biochemical and behavioural study.

Glycine acts as an inhibitory transmitter in the lower brain stem and spinal cord of vertebrate species, while very few data are yet available to support a similar role in invertebrate nervous systems. Here we report the identification and characterization of glycine receptors in the freshwater polyp Hydra vulgaris (Cnidaria, Hydrozoa) by biochemical and behavioural studies. Saturation experiments revealed the occurrence of one population of binding sites of nanomolar affinity (KD = 33 nm) and low capacity (Bmax = 79 fmol/mg protein) for [(3)H]strychnine. The addition of glycine or taurine (0.1 microm-1 mm) produced a dose-dependent inhibition of [(3)H]strychnine binding. Beta-alanine (0.1-1 mm) did not significantly affect [(3)H]strychnine binding. The pharmacological properties of these receptors compare with those of vertebrate glycine receptors. Stimulation of Hydra polyps by reduced glutathione resulted in a significant increase in the duration of mouth opening in the presence of glycine, taurine or beta-alanine. The enhancement of the response was related both to amino acid (10-100 microm) and to glutathione concentration (1-10 microm). The effects of glycine or its agonists were suppressed by strychnine (1-10 microm). D-serine, a glycine agonist at the vertebrate NMDA receptor, produced opposite effects to those of glycine. The effects of d-serine were suppressed by 5,7-dichlorokynurenic acid but not by strychnine. In vitro, [(3)H]strychnine binding was not displaced by d-serine. These results indicate a dual action of glycine in Hydra tissues. The hypothesis that NMDA receptors may also be present in this elementary nervous system is proposed.

Animals↗
PubMed1975

Chemical nature of bioluminescence systems in coelenterates.

Analysis of substances involved in light-emitting reactions among bioluminescent coelenterates has revealed a pronounced uniformity in the structural features of initial reactants, i.e., "luciferins" and photo-protein chromophores, as well as the light-emitter product. This product is structurally identical among the different classes of coelenterates: Hydrozoa (the jellyfish, Aequorea), Anthozoa (the sea cactus, Cavernularia; sea pansy, Renilla; and sea pen, Leioptilus), and very likely also the Scyphozoa (the jellyfish, Pelagia). In each of these instances the reaction product, namely, 2-(p-hydroxy-pnenylacetyl)amino-3-benzyl-5-(p-hydroxyphenyl) pyrazine, is the actual light-emitter, whether it occurs in a Ca2+-triggered photoprotein type of luminescence, or in a "luciferin-luciferase" type. The evidence indicates that in certain coelenterates, e.g., Cavernularia, these two types are equally significant, whereas in others (Renilla and Leioptilus) the "luciferin-luciferase" type predominates over the Ca-triggerable photoprotein type, and finally that only the photoprotein type functions in the luciferaseless jellyfish, Aequorea. In all instances investigated, the structure of the light-emitter prior to the luminescence reaction appears to be essentially the same as that of the chromophore of unreacted aequorin. The product of the luminescence reaction is absent in extracts of non luminous species. However, a product very similar to that of luminescent coelenterates occurs also in representatives of other phyla, including the cephalopod molluscs, e.g., the "firefly squid" Watasenia and probably various ctenophores as well.

Animals↗
PubMed1976

Propagated spikes and secretion in a coelenterate glandular epithelium.

The rete mirabile of Hippopodius (Cl. Hydrozoa, O. Siphonophora) is a sheet of giant endoderm cells penetrated by branches of the ventral radial canal. The cells appear to be highly polyploid. The rough ER is very richly developed and expanded ER cisternae containing amorphous material (presumably synthesized protein) are observed near the outer cell surface. The cells are electrically coupled, and are connected by gap junctions. The rete is electrically excitable and cell to cell conduction of action potentials at 10 cm/s is observed. The action potentials are all-or-none, positive-going events, showing amplitudes of about 70 mV and arising from a 44 mV resting potential. Slowly developing and decaying secondary depolarizations, capable of summing to the 20 mV level, are also observed. After passage of a train of impulses, the rete cells swell and secretion drops appear at the surface, these changes becoming apparent within a few seconds. In 15 mM Mn2+ the response fails to occur, and secondary depolarizations ("secretion potentials") are not seen. Spike propagation is not affected. In Na+-free solutions the spikes are reduced and propagation eventually fails. It is suggested that the spikes are sodium-dependent events which trigger a calcium-dependent secretory process. The composition and biological activity of the secretion are uncertain, but indirect evidence suggests a possible defensive or repellant role for the response.

Action Potentials↗
PubMed2003

Placozoa are not derived cnidarians: evidence from molecular morphology.

The phylum Placozoa is represented by a single known species, Trichoplax adhaerens, a tiny marine organism that represents the most simple metazoan bauplan. Because of the latter, placozoans were originally considered the most basal metazoan phylum. A misinterpretation of the life cycle at the turn of the century and some more recent molecular phylogenetic analyses have placed Trichoplax as a derived species within the Cnidaria. The latter hypothesis assumes that the primitive organization of the Placozoa is the result of secondary reduction. Here we compare the molecular morphology of the predicted 16S rDNA structure and the mitochondrial genome between Trichoplax and representatives of all four cnidarian classes. Trichoplax shares a circular mtDNA molecule as a plesiomorphy with all other metazoans except for the derived cnidarian classes Hydrozoa, Scyphozoa, and Cubozoa. The predicted secondary structure of the 16S rRNA molecule differs substantially between Trichoplax and cnidarians, particularly with respect to the number and length of stem and loop regions. The new molecular morphological characters provide compelling evidence that Trichoplax is not a derived (medusozoan) cnidarian. Furthermore, it was found that the mitochondrial genome in Cubozoa consists of four linear molecules instead of a single circular molecule or two linear molecules, suggesting that the cubozoans may represent the most derived cnidarian group.

Animals↗
PubMed2004

Putative NMDA receptors in Hydra: a biochemical and functional study.

The feeding behaviour of the freshwater polyp Hydra vulgaris (Cnidaria, Hydrozoa) is modulated by a number of molecules acting as neurotransmitters in other nervous systems. Here we present biochemical and functional evidence of the occurrence of putative NMDA receptors in Hydra tissues. Saturation experiments showed the presence of one population of binding sites with nanomolar affinity and low capacity for [3H]MK-801. Before equilibrium, [3H]MK-801 binding was increased by the agonists glutamate and glycine as well as by reduced glutathione (GSH). In vivo the glutamate receptor agonist NMDA markedly decreased the duration of the response to GSH. This effect was linearly related to ligand doses in the nanomolar concentration range and was counteracted by either the NMDAR-specific antagonist D-AP5 or by the d-serine antagonist DCKA. When NMDA concentration was increased to 10 or 100 microm, duration of the response to GSH was no longer affected unless the lectin concanavalin A, which prevents receptor desensitization in other systems, was added to the test medium. Simultaneous administration of ineffective doses of NMDA and strychnine, glycine or d-serine, an agonist at the glycine binding site of the NMDA receptor in vertebrate CNS, resulted in a strong reduction of response duration. Both D-AP5 and DCKA suppressed this effect. These results, together with the decrease in response duration produced by d-serine, support the hypothesis that NMDA-like glutamate receptors may occur in Hydra tissues where they are involved in modulation of the response to GSH with opposite actions to those of GABA and glycine.

2-Amino-5-phosphonovalerate↗
PubMed1969

Inhibition of hydroid aging in Campanularia flexuosa.

Hydranths of the colonial marine hydroid Campanularia flexuosa (phylum Cnidaria, class Hydrozoa, order Calyptoblastea) have a mean life span of approximately 7 days in intact colonies in culture. Hydranths then regress and are absorbed, and their cellular materials are utilized by the colony for continued growth. Hydranth life spans can be extended to 20 days in isolated hydranths if, repeatedly, the pedicel is damaged by pinching and is allowed to partially regen-erate. This suggests that tissue damage and reorganization function to maintain the hydranth.

Aging↗
PubMed1993

Expression of Cnox-2, a HOM/HOX homeobox gene in hydra, is correlated with axial pattern formation.

Cnox-2 is a HOM/HOX homeobox gene that we have identified in the simple metazoan Hydra vulgaris (Cnidaria: Hydrozoa). Cnox-2 is most closely related to anterior members of the Antennapedia gene complex from Drosophila, with the greatest similarity to Deformed. The Cnox-2 protein is expressed in the epithelial cells of adult hydra polyps in a region-specific pattern along the body axis, at a low level in the head and at a high level in the body column and the foot. The expression pattern of Cnox-2 is consistent with a role in axial pattern formation. Alteration of hydra axial patterning by treatment with diacylglycerol (DAG) results in an increase of head activation down the body column and in a coordinate reduction of Cnox-2 expression in epithelial cells in 'head-like' regions. These results suggest that Cnox-2 expression is negatively regulated by a signaling pathway acting through protein kinase C (PKC), and that the varying levels of expression of Cnox-2 along the body axis have the potential to result in differential gene expression which is important for hydra pattern formation.

Amino Acid Sequence↗
PubMed2002

Morphology, swimming performance and propulsive mode of six co-occurring hydromedusae.

Jet propulsion, based on examples from the Hydrozoa, has served as a valuable model for swimming by medusae. However, cnidarian medusae span several taxonomic classes (collectively known as the Medusazoa) and represent a diverse array of morphologies and swimming styles. Does one mode of propulsion appropriately describe swimming by all medusae? This study examined a group of co-occurring hydromedusae collected from the waters of Friday Harbor, WA, USA, to investigate relationships between swimming performance and underlying mechanisms of thrust production. The six species examined encompassed a wide range of bell morphologies and swimming habits. Swimming performance (measured as swimming acceleration and velocity) varied widely among the species and was positively correlated with bell streamlining (measured as bell fineness ratio) and velar structure development (measured as velar aperture ratio). Calculated thrust production due to jet propulsion adequately explained acceleration patterns of prolate medusae (Aglantha digitale, Sarsia sp. and Proboscidactyla flavicirrata) possessing well-developed velums. However, acceleration patterns of oblate medusae (Aequorea victoria, Mitrocoma cellularia and Phialidium gregarium) that have less developed velums were poorly described by jet thrust production. An examination of the wakes behind swimming medusae indicated that, in contrast to the clearly defined jet structures produced by prolate species, oblate medusae did not produce defined jets but instead produced prominent vortices at the bell margins. These vortices are consistent with a predominantly drag-based, rowing mode of propulsion by the oblate species. These patterns of propulsive mechanics and swimming performance relate to the role played by swimming in the foraging ecology of each medusa. These patterns appear to extend beyond hydromedusae and thus have important implications for other members of the Medusazoa.

Animals↗
PubMed2004

Evidence for a common pattern of peptidergic innervation of cnidocytes.

Tentacles from representatives of all four classes of the phylum Cnidaria were examined using antibodies against the neuropeptides FMRFamide and RFamide to reveal the organization of neurons and nerve nets associated with cnidocytes. The tentacles of all species examined contained FMRFamide- or RFamide-immunoreactive neurons, in varying densities. In representatives from the Scyphozoa, Hydrozoa, and Cubozoa, the FMRFamide-immunoreactive neurons formed plexuses at the base of the cnidocyte assemblages; in anthozoans, the absence of discrete assemblies of cnidocytes precluded visual co-localization of cnidocytes and immunoreactive neurons. In all four classes, immunoreactive sensory cells connected these peptidergic nerve nets to the surface of the tentacle. These findings suggest that members of all four cnidarian classes share a common organizational pattern, and it is proposed that this peptidergic innervation may be involved in the chemosensory regulation of cnidocyte discharge.

Animal Structures↗
PubMed1999

[Dangerous marine animals].

Sea-biological basic knowledge for divers is offered only in special lessons for advanced scuba divers. According to statistics, however, five per cent of the deadly diving accidents are caused by underwater organisms. This number could be reduced to a fraction, by correct behaviour during the dive and after an accident. The most frequent accidents with sea animals during water sports are not by unprovoked shark attacks, which cause six deaths world-wide per year on the average, but turn out with usually well camouflaged sea inhabitants, that do not attack humans, rather by their inadvertence coincidentally get in contact with it. The various defense instruments of the often small, inconspicuous organisms reach from teeth over poison stings, pricks, spines, scalpelles, nettle injections and chemical weapons up to poison arrows. Due to that variety of the maritime life, the most important representatives of its type are explained including severity level of the caused injury or contamination. Both, diagnostic position and therapy possibility are described as follows: 1. Porifera (sponge), 2. Hydrozoa (white weed, yellow flower head), Actinaria (sea anemones), 3. Conidae (cone shells), Tridocna (giant clam), octopoda (octopus), 4. Acanthaster planci (crown of thorns), Echinodea (sea urchins), Holothurioidea (sea cucumber), 5. Selachoidei (shark), Batoidei (Ray), Muraenidae (moray), Plotosidae (barbel eels), Synanciidae (stonefish), Scorpaenidae (scorpionfish), Pterois (lion fish), Sphyraena Spec. (barracuda), Balistidae (triggerfish), Ostracionidae (puffer).

Animals↗
PubMed2001

The interrelationships of metazoan parasites: a review of phylum-and higher-level hypotheses from recent morphological and molecular phylogenetic analyses.

Phylogeny of seven groups of metazoan parasitic groups is reviewed, based on both morphological and molecular data. The Myxozoa (=Malacosporea + Myxosporea) are most probably related to the egg-parasitic cnidarian Polypodium (Hydrozoa?: Polypodiozoa); the other phylogenetic hypotheses are discussed and the possible non-monophyly of the Cnidaria (with the Polypodiozoa-Myxozoa clade closest to the Triploblastica) is suggested. The Mesozoa is a monophyletic group, possibly closely related to the (monophyletic) Acoelomorpha; whether the Acoelomorpha and Mesozoa represent the basalmost triploblast clade(s) or a derived platyhelminth subclade may depend on rooting the tree of the Triploblastica. Position of the monophyletic Neodermata (=Trematoda + Cercomeromorpha) within the rhabditophoran flatworms is discussed, with two major alternative hypotheses about the neodermatan sister-group relationships (viz., the "neoophoran" and "revertospermatan"). The Myzostomida are not annelids but belong among the Platyzoa, possibly to the clade of animals with anterior sperm flagella (=Prosomastigozoa). The Acanthocephala represent derived syndermates ("rotifers"), possibly related to Seison (the name Pararotatoria comb. n. is proposed for Seisonida + Acanthocephala). The crustacean origin of the Pentastomida based on spermatological and molecular evidence (Pentastomida + Branchiura = Ichthyostraca) is confronted with palaeontological views favouring the pre-arthropod derivation of the pentastomids. Phylogenetic position of the nematodes within the Ecdysozoa and evolution of nematode parasitism are discussed, and the lack of relevant information about the enigmatic ectoproctan parasite Buddenbrockia is emphasised.

Animals↗