Adaptation morphologique de l'acrorrhage chez Actinia equina L.

Résumé L'analyse ultra-structurale de l'acrorrhage d'Actinia equina L. a permis de montrer une adaptation histologique au décollement de l'ectoderme lors de la réponse de l'actinie à une agression. La zone basale et digitée des cellules ectodermiques est très vacuolisée. La turgescence de l'acrorrhage provoque une extension de la mésoglée; on observe un écartement des bases cellulaires et la rupture des vésicules facilite la séparation de l'ectoderme et de la mésoglée. Celle-ci a lieu après ancrage des nématocystes atriches dans les tissus de l'agresseur, et retrait de l'Actinie.

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Morphological adaptation of the acrorhagi of Actinia equina L.

Summary The ultrastructural analysis of the acrorhagi of Actinia equina reveals histological adaptations to the specific detachment of this brightly colored strip of ectoderm in case of being attached. The basal zone of the ectoderm cells is highly vacuolated. The turgidity of the acrorhagous provokes an extension of the mesoglea. The separation of the ectoderm is facilitated by rupture of the vacuoles and the specific arrangement of the filament containing branched bases of the cells. When the ectoderm, which contains numerous nematocysts, is fixed in the tissue of a agressor, this one detaches.

     

Laceration,knospung und heteromorphose bei Actinia equina L.

Ohne Zusammenfassung     

Cobalt Staining Of Actinia Equina Nematocysts

Nematocysts of Actinia equina are stained black by incubation in 2% CoCl₂ followed by an aqueous wash and H₂S treatment. They are also stained positively by morin. Nematocysts isolated from the acrorhage were found to have a high concentration of calcium of which only 30% was “free.' It is suggested that the high concentration of calcium in the nematocysts accounts for their staining by cobalt and morin. Cobalt staining offers a simple and effective technique for investigation of nematocysts.     

Cathepsin S and cruzipain are inhibited by equistatin from Actinia equina.

Cathepsin S has been isolated for the first time from human tissue. It has a molecular mass of 24 kDa and an isoelectric point in the range of 8.2 to 8.6. The enzyme is inhibited by equistatin, which belongs to the thyropins, a new family of protein inhibitors, with an inhibition constant of Ki = 0.40 +/- 0.07 nM. Cruzipain, a cathepsin L-like enzyme sharing a 130 amino acid long C-terminal extension, is also strongly inhibited by equistatin (Ki = 0.028 +/- 0.006 nM). Together with previously reported data, these results further indicate that a functional heterogeneity exists among thyropin inhibitors, as demonstrated by their interaction with cathepsin S and cruzipain.     

Experimental habituation of aggression in the sea anemone Actinia equina

Behavioural plasticity in Actinia equina (L.) was examined in experimental contests using a range of pedal disc colour phenotypes, which characterize 3 known, ecologically distinct morphs. With repeated pairing of individuals in auto-phenotypic encounters, habituation was easily induced in the 2 mid-shore morphs, but was not obvious in the less aggressive, low-shore form. Subsequent pairing with a different partner revealed that anemones remained aggressive towards a novel opponent. Following novel contact, repairing of the dark red pedal phenotype with the original partner provided some evidence of retention of habituation to a previous opponent, and thus of a specific inducible memory.     

Actions of adenylyl compounds in the pedal disc of the cnidarian Actinia equina

1. The actions of adenylyl compounds were investigated in the circular muscle of the pedal disc of the sea anenome Actinia equina.2. Adenosine, adenosine 5'-diphosphate and adenosine 5'-triphosphate (ATP), but not adenosine 5'-monophosphate or the analogues of ATP, α,β-methylene ATP, and 2-methylthio ATP, caused concentration-dependent contractions.3. Neurogenic contractions in response to electrical field stimulation were not consistently affected by any of the adenylyl compounds and could be either potentiated or almost abolished by them.4. Reactive Blue 2, a vertebrate P₂-purinoceptor antagonist, caused concentration-dependent contractions which were mediated by nerves, being blocked by the anaesthetic chlorobutanol.5. The pharmacological profile of the adenylyl compounds in the pedal disc of Actinia equina is different from that observed in other invertebrate species and adds to the greater diversity of such profiles in invertebrates than in vertebrates.     

Possible cryptic speciationwithin the sea anemone Actinia equina complex detected byAFLP markers

The population genetic profiles of 60 specimens of thecommon intertidal sea anemone Actinia equina taken from foursampling sites (Peroj, Barbariga and the north and south shoresof the Limski Canal), along a 25 km strip of the coastof the Istra Peninsula, Croatia, were evaluated by AFLP markers(144 loci). All populations were characterized by aggregates ofspecimens confined within a few square meters. One of the populations(on the north shore of the canal) contained both large and small-sizedindividuals. Results revealed high within-aggregate genetic heterogeneity(36.1–55.6%). With respect to interpopulationprofiles, geographically remote populations from Peroj, Barbarigaand the south shore of the canal were more closely related geneticallythan those on the north and south shores of the canal. The small-sizedsubpopulation from the north shore exhibits a distinct AFLP pattern,suggesting that it warrants recognition as a cryptic species.  © 2002The Linnean Society of London, Zoological Journal of the LinneanSociety , 2002, 136 , 315−320     

Primary structure of a potassium channel toxin from the sea anemone Actinia equina

A potassium channel toxin (AeK) was isolated from the sea anemone Actinia equina by gel filtration on Sephadex G-50 and reverse-phase HPLC on TSKgel ODS-120T. AeK and α-dendrotoxin inhibited the binding of ¹²⁵I-α-dendrotoxin to rat synaptosomal membranes with IC₅₀ of 22 and 0.34 nM, respectively, indicating that AeK is about sixty-five times less toxic than α-dendrotoxin. The complete amino acid sequence of AeK was elucidated; it is composed of 36 amino acid residues including six half-Cys residues. The determined sequence showed that AeK is analogous to the three potassium channel toxins from sea anemones (BgK from Bunodosoma granulifera, ShK from Stichodactyla helianthus and AsKS from Anemonia sulcata), with an especially high sequence homology (86%) with AsKS.     

Toxicity of Actinia equina (Cnidaria: Anthozoa) crude venom on cultured cells

The toxicity of Cnidaria is a subject of high concern owing to its influence on human activities and public health and to the implications in ecological relationships between organisms. In order to simulate as much as possible the natural conditions and the consequences of stinging against injured cells, as well considering that Cnidarian venoms are located not only in nematocysts but also in tissues, the cytotoxicity and genotoxicity of crude extracts from nematocyst and surrounding tissues of the sea-anemone Actinia equina (Cnidaria: Anthozoa) were assessed on cultured fibroblasts (V79). The cytotoxicity was remarkable and cell survival was highly reduced at highest tested concentration (150,000 nematocysts/ml); using the Trypan blue dye exclusion test, only 40% of treated cells survived after the first hour of treatment and viable cells were not counted after the second hour. Also the results obtained utilizing the Neutral Red assay showed serious effects of crude toxin (only 31.5% and 12.6% cell survival after one and three hours respectively). Genotoxic effects were not observed at tested doses.     

The cytotoxic and cytolytic activity of equinatoxin II from the sea anemone Actinia equina

The cytotoxic and cytolytic effects of equinatoxin II (EqT II) from the sea anemone Actinia equina L. were studied on exponentially growing and synchronized V-79-379 A cell line in culture. The cell viability test and the determination of the cytolytic effect by cell counting confirmed both cytotoxic and cytolytic activity of EqT II. Additionally, cytocidal and cytostatic effects depending on the toxin concentration were observed. The presence of fetal calf serum in the cell culture medium reduced both cytocidal and cytostatic effects by two magnitudes and prevented cytolysis. Combining EqT II and serum resulted in an insoluble complex which was cytostatic even when isolated and resuspended in the culture medium, while the supernatant retained both cytocidal and cytostatic activity. No significant difference in sensitivity between synchronized and exponentially growing cells could be detected after EqT II treatment.     

Transformations of the Chromophore in the Course of Maturation of a Chromoprotein from Actinia equina

Russian Journal of Bioorganic Chemistry - Currently, it is generally accepted that chromophore synthesis of red fluorescent proteins proceeds via an intermediate “blue” form with a...     

Lipid phase coexistence favors membrane insertion of equinatoxin-II, a pore-forming toxin from Actinia equina

Equinatoxin-II is a eukaryotic pore-forming toxin belonging to the family of actinoporins. Its interaction with model membranes is largely modulated by the presence of sphingomyelin. We have used large unilamellar vesicles and lipid monolayers to gain further information about this interaction. The coexistence of gel and liquid-crystal lipid phases in sphingomyelin/phosphatidylcholine mixtures and the coexistence of liquid-ordered and liquid-disordered lipid phases in phosphatidylcholine/cholesterol or sphingomyelin/phosphatidylcholine/cholesterol mixtures favor membrane insertion of equinatoxin-II. Phosphatidylcholine vesicles are not permeabilized by equinatoxin-II. However, the localized accumulation of phospholipase C-generated diacylglycerol creates conditions for toxin activity. By using epifluorescence microscopy of transferred monolayers, it seems that lipid packing defects arising at the interfaces between coexisting lipid phases may function as preferential binding sites for the toxin. The possible implications of such a mechanism in the assembly of a toroidal pore are discussed.     

Gametogenic cycles and reproduction in the beadlet sea anemone Actinia equina (Cnidaria: Anthozoa)

Sexual Actinia equina have been maintained in the laboratory. Monthly biopsies show that these animals have annual gametogenic cycles. Regular samples from several natural populations suggest that animals in the wild show similar gametogenic periodicity. In the laboratory, males release sperm, but females brood young, at least for a few weeks. Members of these broods are released sporadically, usually after a water change. Males and non-sexual adults kept in isolation for over a year release a few juveniles during and at the end of that time. These young are likely to be asexually reproduced. There appears to be geographical variation of anemone size and in the frequency of sexual individuals in populations round the British Coast, so that modes of reproduction may vary.     

High in situ repeatability of behaviour indicates animal personality in the beadlet anemone Actinia equina (Cnidaria)

'Animal personality' means that individuals differ from one another in either single behaviours or suites of related behaviours in a way that is consistent over time. It is usually assumed that such consistent individual differences in behaviour are driven by variation in how individuals respond to information about their environment, rather than by differences in external factors such as variation in microhabitat. Since behavioural variation is ubiquitous in nature we might expect 'animal personality' to be present in diverse taxa, including animals with relatively simple nervous systems. We investigated in situ startle responses in a sea anemone, Actinia equina, to determine whether personalities might be present in this example of an animal with a simple nervous system. We found very high levels of repeatability among individuals that were re-identified in the same locations over a three week sampling period. In a subset of the data, where we used tide-pool temperature measurements to control for a key element of variation in microhabitat, these high levels of repeatability remained. Although a range of other consistent differences in micro-habitat features could have contributed to consistent differences between the behaviour of individuals, these data suggest the presence of animal personality in A. equina. Rather than being restricted to certain groups, personality may be a general feature of animals and may be particularly pronounced in species with simple nervous systems.     

Effect of cobalt ions on lipid and sterol metabolism in the marine invertebrates Mytilus galloprovincialis and Actinia equina

The lipid and sterol fractions of the mussel Mytilus galloprovincialis and the anemone Actinia equina were analyzed before and after incubation with cobalt ions. There were significant changes in the lipid and sterol composition, strongly depending on the cobalt ions concentrations. The changes in the lipid composition of both invertebrates were different for neutral lipids and phospholipids. These changes concern the length of the fatty acid chains as well as their unsaturation. The cobalt ions inhibited the oxidation of sterols and their alkylation at C-24. Because of these results we can assume that some of the changes caused by cobalt ions might possess adaptive value.     

Crystal structure of the soluble form of equinatoxin II, a pore-forming toxin from the sea anemone Actinia equina

BACKGROUND: Membrane pore-forming toxins have a remarkable property: they adopt a stable soluble form structure, which, when in contact with a membrane, undergoes a series of transformations, leading to an active, membrane-bound form. In contrast to bacterial toxins, no structure of a pore-forming toxin from an eukaryotic organism has been determined so far, an indication that structural studies of equinatoxin II (EqtII) may unravel a novel mechanism. RESULTS: The crystal structure of the soluble form of EqtII from the sea anemone Actinia equina has been determined at 1.9 A resolution. EqtII is shown to be a single-domain protein based on a 12 strand beta sandwich fold with a hydrophobic core and a pair of alpha helices, each of which is associated with the face of a beta sheet. CONCLUSIONS: The structure of the 30 N-terminal residues is the largest segment that can adopt a different structure without disrupting the fold of the beta sandwich core. This segment includes a three-turn alpha helix that lies on the surface of a beta sheet and ends in a stretch of three positively charged residues, Lys-30, Arg-31, and Lys-32. On the basis of gathered data, it is suggested that this segment forms the membrane pore, whereas the beta sandwich structure remains unaltered and attaches to a membrane as do other structurally related extrinsic membrane proteins or their domains. The use of a structural data site-directed mutagenesis study should reveal the residues involved in membrane pore formation.