Adenylate cyclase in sea anemone implication for chemoreception

Adenylate cyclase of the sea anemoneAnthopleura elegantissima was found to be associated with the heavy particulate fraction of the cell and to be activated by NaF and 2-mercaptoethanol. Reduced glutathione, which elicits the ciliary swallowing response during feeding, also activated adenylate cyclase in particles from the oral disc and pharynx. The GSH effect was dependent on homogenization procedure, whereas the NaF and 2-mercaptoethanol activation was not. The activation of adenylate cyclase from the oral disc and pharynx by GSH was correlated with increased Ca²⁺ binding to the particulate fraction. When activation by GSH was abolished by mechanical homogenization, no increasea in Ca²⁺ binding was observed in the presence of GSH. It is suggested that chemoreception for the swallowing response of this organism is mediated by cyclic AMP control of Ca²⁺ distribution in the cell.     

Internal brooding favours pre-metamorphic chimerism in a non-colonial cnidarian, the sea anemone Urticina felina

The concept of intraorganismal genetic heterogeneity resulting from allogeneic fusion (i.e. chimerism) has almost exclusively been explored in modular organisms that have the capacity to reproduce asexually, such as colonial ascidians and corals. Apart from medical conditions in mammals, the natural development of chimeras across ontogenetic stages has not been investigated in any unitary organism incapable of asexual propagation. Furthermore, chimerism was mainly studied among gregarious settlers to show that clustering of genetically similar individuals upon settlement promotes the occurrence of multi-chimeras exhibiting greater fitness. The possible occurrence of chimeric embryos and larvae prior to settlement has not received any attention. Here we document for the first time the presence of natural chimeras in brooded embryos and larvae of a unitary cnidarian, the sea anemone Urticina felina. Rates of visible bi- and multi-chimerism of up to 3.13 per cent were measured in the broods of 16 females. Apart from these sectorial chimeras, monitored fusion events also yielded homogeneous chimeric entities (mega-larvae) suggesting that the actual rates of natural chimerism in U. felina are greater than predicted by visual assessment. In support of this assumption, the broods of certain individuals comprised a dominant proportion (to 90%) of inexplicably large embryos and larvae (relative to oocyte size). Findings of fusion and chimerism in a unitary organism add a novel dimension to the framework within which the mechanisms and evolutionary significance of genetic heterogeneity in animal taxa can be explored.     

Toxins of the sea anemone Epiactis prolifera

Fe³⁺-EDTA chelates react with the superoxide radical at physiological pH values (k = 1.3 × 10⁶M^?1 s^?1 at pH 7 but is lower at more alkaline pH values) but do not appear to catalyze O₂^? dismutation at a significant rate. Complexes of Fe³⁺ with desferrioxamine, bathophenanthroline, or diethylenetriaminepentaacetic acid react much more slowly, if at all. Fe²⁺ complexes of EDTA, ATP, and diethylenetriaminepentaacetic acid also react with O₂^? at alkaline pH values. The significance of these reactions in the mechanism of the “iron-catalyzed Haber-Weiss reaction” is discussed.     

Control of shell settling in the swimming sea anemone Stomphia coccinea.

1. Electrical activity has been recorded from Stomphia coccinea during the behavioural sequence in which the detached anemone settles on to a Modiolus shell. 2. When a responsive tentacle contacts the shell, a short, complex burst of pulses is elicited. These remain confined to the region of contact. The endodermal slow-conduction system (SS2) then begins to fire repetitively (a typical example is 16 SS2 pulses at a mean interpulse interval of 5 s) until the pedal disc begins to inflate. Shell-tentacle contact is essential for stimulation of SS2 activity. 3. The complete response, apart from local bending of the column, may be reproduced by electrical stimulation of the SS2 alone. As few as 10 stimuli at frequencies between 1 shock/s and 1 shock/10 s are required to elicit the response.     

Calitoxin, a neurotoxic peptide from the sea anemone Calliactis parasitica: amino acid sequence and electrophysiological properties

We have isolated a new toxin, calitoxin (CLX), from the sea anemone Calliactis parasitica whose amino acid sequence differs greatly from that of other sea anemone toxins. The polypeptide chain contains 46 amino acid residues, with a molecular mass of 4886 Da and an isoelectric point at pH 5.4. The amino acid sequence determined by Edman degradation of the reduced, S-carboxymethylated polypeptide chain and tryptic and chymotryptic peptides is Ile-Glu-Cys-Lys-Cys-Glu-Gly-Asp-Ala-Pro-Asp-Leu-Ser-His-Met-Thr-Gly-Thr- Val-Tyr - Phe-Ser-Cys-Lys-Gly-Gly-Asp-Gly-Ser-Trp-Ser-Lys-Cys-Asn-Thr-Tyr-Thr-Ala- Val-Ala - Asp-Cys-Cys-His-Glu-Ala. No cysteine residues were present in the peptide. Similarly to other sea anemone toxins, calitoxin interacts, in crustacean nerve muscle preparations, with axonal and not with muscle membranes, inducing a massive release of neurotransmitter that causes a strong muscle contraction. The low homology of CLX with RP II and ATX II toxins has implications regarding the role played by particular amino acid residues.     

Genetics and asexual reproduction of the sea anemone Metridium senile.

1. Metridium senile was studied for phosphohexose-isomerase variation at three locations on Cape Cod, Massachusetts: Woods Hole, Cape Cod Canal, and Barnstable Town Boat Harbor. 2. All three locations exhibited significant polymorphism for PHI. 3. Mapping of individual polyps was performed at Barnstable to analyze spatial distributions of clones and genotypes. 4. In Barnstable, PHI does not depart significantly from Hardy-Weinberg expectations at the time of establishment of new polyps, and establishment of larvae is spatially random with respect to PHI genotype. 5. Asexual reproduction was uses as a meausre of the relative success of different PHI genotypes. There are indications that not all genotypes are equally likely to produce large clones. 6. There is significant heterogeneity among the three locations with respect to PHI genotype frequencies, suggesting that there may be geographical differentiation of the populations. 7. Sessile, asexual organisms provide powerful tools for examining the dynamic aspects of genetic structure in natural populations.     

NMR analysis and sequence of toxin II from the sea anemone Radianthus paumotensis

Toxin II from Radianthus paumotensis (RpII) has been investigated by high-resolution NMR and chemical sequencing methods. Resonance assignments have been obtained for this protein by the sequential approach. NMR assignments could not be made consistent with the previously reported primary sequence for this protein, and chemical methods have been used to determine a sequence with which the NMR data are consistent. Analysis of the 2D NOE spectra shows that the protein secondary structure is comprised of two sequences of beta-sheet, probably joined into a distorted continuous sheet, connected by turns and extended loops, without any regular alpha-helical segments. The residues previously implicated in activity in this class of proteins, D8 and R13, occur in a loop region.     

Nervous control of light responses in the sea anemone, Calamactis praelongus.

1. The burrowing sea anemone, Calamactis praelongus, responds to light with local, non-nervous contractions of the column. There are also more extensive responses of the column and retractor muscles co-ordinated by nerve net pulses (NNP's) under pacemaker control. 2. NNP's occur in at least two types of bursts and in sequences which sometimes indicate a rotating site of pulse initiation. 3. Light-evoked NNP sequences can be tape recorded and used later to drive a stimulator to reproduce the original sequences in the same or different anemones, evoking muscular responses which approximate the originals. This technique separates the pacemaker-directed component of the light response from the local effects of light stimulation. 4. Isolated circular and parietal muscles contract slowly when stimulated by light or excited indirectly by NNP's. Retractor muscles are insensitive to light but produce rapid contractions when excited by closely spaced light-evoked NNP's. 5. A model for light responses is proposed which incorporates the characteristics of isolated muscles and intact anemones.     

Ammonium metabolism in the symbiotic sea anemone Anemonia viridis

The temperate sea anemone Anemonia viridis (Forskål) forms an endosymbiotic association with dinoflagellate algae commonly referred to as zooxanthellae. It is now well established that under appropriate environmental conditions, these associations can be autotrophic for carbon. Under such conditions, many of these symbioses, including A. viridis, not only retain excretory ammonium, but can take up ammonium added to the surrounding seawater. The flux from inorganic to organic nitrogen will be via the free amino acid pools and in A. viridis these were found to be markedly different between zooxanthellae and host with glycine and taurine dominant in the latter. When anemones were maintained with 20 M ammonium, the concentration of free amino groups increased in the zooxanthellae but appeared not to change in the host. There was no evidence that the ratio of glutamine – glutamate in zooxanthellae changed when anemones were maintained with 20 M ammonium for 47 days. These ratios imply that zooxanthellae from this temperate symbiosis may not be nitrogen-limited. GDH was detected in both zooxanthellae and host where it was most active with the coenzyme NADPH. In addition, GDH showed activity when glutamine replaced ammonium as the substrate, indicating that the host may have alternative means to assimilate ammonium. Zooxanthellae were shown to possess GOGAT activity in the presence of a ferredoxin analogue. This suggests that in vivo zooxanthellae could assimilate ammonium via the activity of GS linked with ferredoxin-dependent GOGAT. Given evidence from other studies of rapid ammonium assimilation and essential amino acid synthesis in symbiotic host tissue, it appears that the capacity of cnidarians to metabolise nitrogen may at present be underestimated.     

Proline inhibition of a sea anemone alarm pheromone response.

1. L-proline, by itself or in animal tissue extracts, inhibits the response of the sea anemone Anthopleura elegantissima to the alarm phermone, anthopeurine. 2. The effect of proline is mediated by a receptor that is specific for the structure and configuration of the part of the L-proline molecule containing the carboxyl and imino groups. 3. Proline inhibition is competitive, in the sense that the effects of a given proline concentration can be overridden by an increase in anthopeurine concentration. 4. The magnitude of proline inhibition increases with proline concentration and decreases as the duration of exposure to proline increases. 5. Neither the final conducting system mediating the alarm response nor the responding muscles are inhbited by proline. Inhibition presumably occurs at or soon after the level of anthopleurine receptors. 6. Proline inhibition may resolve the potential conflict between Anthopleura's mutually exclusive feeding and alarm pheromone responses.     

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.     

An analysis of the relationship between solubility and stimulating effect in tarsal chemoreception

The rejection thresholds of the blowfly Phormia regina Meigen for a selected series of substituted aliphatic hydrocarbons have been determined and an analysis made of the effect on stimulation of increasing the number of like substitutions from one to two, of the interaction of different types of substituent, and of the position of the substituent in the molecule. The order of stimulating efficiency (reciprocal of rejection threshold) of the functional groups which have been studied is: Br > Cl ? CH₃ ? CHO > C=O > OH. There is a consistent decrease in stimulating effect following the introduction of a second hydroxyl group. The introduction of a second C=O has little effect. Introduction of a second halogen is generally followed by a decrease in threshold. Two different species of functional group, one of which tends to increase water solubility and the other to decrease it, tend to counter-balance each other. A single oxygen-containing functional group on the end of the molecule or two of these groups which are terminal reduce the stimulating effect less than when one or more of such groups are subterminal or located elsewhere within the molecule. Branching of the carbon chain decreases effectiveness. Sulfur and oxygen linkages also decrease effectiveness. In general, the length of the free alkyl group largely determines the stimulating effectiveness. Its power is modified to varying degrees by the nature of the attached polar groups. Of all chemical properties examined, solubility alone agrees consistently with the foregoing data. Threshold varies directly with the molar solubility of the compounds in water. The fact that the threshold values for individual compounds are frequently different from those which would be expected solely on the basis of the correlation between threshold and solubility in water suggests that other factors are also concerned in stimulation. These have not yet been identified.     

Tiny sea anemone from the Lower Cambrian of China

Background

Abundant fossils from the Ediacaran and Cambrian showing cnidarian grade grossly suggest that cnidarian diversification occurred earlier than that of other eumetazoans. However, fossils of possible soft-bodied polyps are scanty and modern corals are dated back only to the Middle Triassic, although molecular phylogenetic results support the idea that anthozoans represent the first major branch of the Cnidaria. Because of difficulties in taxonomic assignments owing to imperfect preservation of fossil cnidarian candidates, little is known about forms ancestral to those of living groups.

Methods and Findings

We have analyzed the soft-bodied polypoid microfossils Eolympia pediculata gen. et sp. nov. from the lowest Cambrian Kuanchuanpu Formation in southern China by scanning electron microscopy and computer-aided microtomography after isolating fossils from sedimentary rocks by acetic acid maceration. The fossils, about a half mm in body size, are preserved with 18 mesenteries including directives bilaterally arranged, 18 tentacles and a stalk-like pedicle. The pedicle suggests a sexual life cycle, while asexual reproduction by transverse fission also is inferred by circumferential grooves on the body column.

Conclusions

The features found in the present fossils fall within the morphological spectrum of modern Hexacorallia excluding Ceriantharia, and thus Eolympia pediculata could be a stem member for this group. The fossils also demonstrate that basic features characterizing modern hexacorallians such as bilateral symmetry and the reproductive system have deep roots in the Early Cambrian.     

Characterization of outer arm dynein in sea anemone, Anthopleura midori.

Outer arm dynein was purified from sperm flagella of a sea anemone, Anthopleura midori, and its biochemical and biophysical properties were characterized. The dynein, obtained at a 20S ATPase peak by sucrose density gradient centrifugation, consisted of two heavy chains, three intermediate chains, and seven light chains. The specific ATPase activity of dynein was 1.3 micromol Pi/mg/min. Four polypeptides (296, 296, 225, and 206 kDa) were formed by UV cleavage at 365 nm of dynein in the presence of vanadate and ATP. In addition, negatively stained images of dynein molecules and the hook-shaped image of the outer arm of the flagella indicated that sea anemone outer arm dynein is two-headed. In contrast to protist dyneins, which are three-headed, outer arm dyneins of flagella and cilia in multicellular animals are two-headed molecules corresponding to the two heavy chains. Phylogenetic considerations were made concerning the diversity of outer arm dyneins.