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PubMed1982

Morphology and morphodynamics of the stenotele nematocyst of Hydra attenuata Pall. (Hydrozoa, Cnidaria).

This light- and electron-microscopic study has investigated the structure, the morphodynamics of discharge, and the impact of the stenotele cyst of Hydra attenuata (Hydrozoa, Cnidaria) on the prey's integument. The triggered capsule, which is ejected from the cell, discharges its tubular content (shaft, stylets and tubule) by a process of evagination. In doing so the three joined stylets punch a hole into the cuticle of the prey through which the long evaginating tubule penetrates into the interior of the target. The behaviour of the tubule is described in detail and the functional significances of the various parts of the capsule are discussed.

Animals↗
PubMed2004

The ancestral role of COE genes may have been in chemoreception: evidence from the development of the sea anemone, Nematostella vectensis (Phylum Cnidaria; Class Anthozoa).

An orthologue of the COE family of helix-loop-helix transcription factors was recovered from the anthozoan Nematostella vectensis (Cnidaria). NvCOE has high sequence similarity to vertebrate and invertebrate orthologues in all three major functional domains of the protein. In situ hybridization studies show early expression through the cleavage period but transcripts are down regulated at gastrulation while remaining expressed at high levels only in the apical tuft of cilia at the aboral end of the planula larva. It is likely that one of the ancestral roles of the COE family of genes may have been in the development of chemosensory neurons.

Animals↗
PubMed1993

A symbiogenetic theory for the origins of cnidocysts in Cnidaria.

Did cnidarian cnidocysts originate from cnidocyst-bearing protoctistans living as symbiotic partners with an epithelial placula? If an increase in the fitness of symbiotic partners was "locked in" by an evolutionary stable strategy, co-evolution and compartmentalization could have led phyletically separate, eukaryotic symbionts to fuse and undergo nuclear merger. Traits originating in the symbiotic partners would have been brought to the "synthetic" organism and reworked through evolution into the development of an integrated organism. Support for the theory of symbiogenetic origins of Cnidaria rests on traces of symbiosis detected in the relationship of cnidarian epithelium to interstitial cells (I-cells), the precursors of cnidocyst-producing cnidoblasts: (1) epithelium and I-cell are autonomous and differ in morphology, cellular dynamics, the relationship of differentiation to proliferation and the variety of cell types formed; (2) hydras and planulas can be "cured" of I-cells and their derivatives, thereby creating "epithelial" animals which lack responsiveness but retain vegetative properties. (3) The reintroduction of I-cells into "epithelial" animals which lack responsiveness but retain vegetative properties. (3) The reintroduction of I-cells into "epithelial" animals restores missing differentiated cell and organismic characteristics. Symbiogenesis as a source of metazoan species has consequences for concepts of development, from the origins of cell lines to the evolution of differentiation.

Animals↗
PubMed1990

Nucleotide sequence of the histone H3-encoding gene from the scleractinian coral Acropora formosa (Cnidaria: Scleractinia).

The histone H3-encoding gene from the staghorn coral Acropora formosa has the 3'-hairpin structure which functions as termination/processing signal in nonpolyadenylated histone mRNAs. The predicted amino acid sequence is highly homologous with the major H3 histones of higher metazoans, and has least homology with the corresponding protist and fungal proteins. These data are inconsistent with the phylogenetic position which has been assigned to the Cnidaria by partial 18S rRNA sequence comparison.

Amino Acid Sequence↗
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↗
PubMed2006

Axial patterning and diversification in the cnidaria predate the Hox system.

Across the animal kingdom, Hox genes are organized in clusters whose genomic organization reflects their central roles in patterning along the anterior/posterior (A/P) axis . While a cluster of Hox genes was present in the bilaterian common ancestor, the origins of this system remain unclear (cf. ). With new data for two representatives of the closest extant phylum to the Bilateria, the sea anemone Nematostella and the hydromedusa Eleutheria, we argue here that the Cnidaria predate the evolution of the Hox system. Although Hox-like genes are present in a range of cnidarians, many of these are paralogs and in neither Nematostella nor Eleutheria is an equivalent of the Hox cluster present. With the exception of independently duplicated genes, the cnidarian genes are unlinked and in several cases are flanked by non-Hox genes. Furthermore, the cnidarian genes are expressed in patterns that are inconsistent with the Hox paradigm. We conclude that the Cnidaria/Bilateria split occurred before a definitive Hox system developed. The spectacular variety in morphological and developmental characteristics shown by extant cnidarians demonstrates that there is no obligate link between the Hox system and morphological diversity in the animal kingdom and that a canonical Hox system is not mandatory for axial patterning.

Animals↗
PubMed2006

Phylogenetic analysis with multiple markers indicates repeated loss of the adult medusa stage in Campanulariidae (Hydrozoa, Cnidaria).

The Campanulariidae is a group of leptomedusan hydroids (Hydrozoa, Cnidaria) that exhibit a diverse array of life cycles ranging from species with a free medusa stage to those with a reduced or absent medusa stage. Perhaps the best-known member of the taxon is Obelia which is often used as a textbook model of hydrozoan life history. However, Obelia medusae have several unique features leading to a hypothesis that Obelia arose, in a saltational fashion, from an ancestor that lacked a medusa, possibly representing an example of a rare evolutionary reversal. To address the evolution of adult sexual stages in Campanulariidae, a molecular phylogenetic approach was employed using two nuclear (18S rDNA and calmodulin) and two mitochondrial (16S rDNA and cytochrome c oxidase subunit I) genes. Prior to the main analysis, we conducted a preliminary analysis of leptomedusan taxa which suggests that Campanulariidae as presently considered needs to be redefined. Campanulariid analyses are consistent with morphological understanding in that three major clades are recovered. However, several recognized genera are not monophyletic calling into question some "diagnostic" features. Furthermore, ancestral states were reconstructed using parsimony, and a sensitivity analysis was conducted to investigate possible evolutionary transitions in life-history stages. The results indicate that life-cycle transitions have occurred multiple times, and that Obelia might be derived from an ancestor with Clytia-like features.

Animals↗
PubMed2005

Hydralysins, a new category of beta-pore-forming toxins in cnidaria.

Cnidaria are venomous animals that produce diverse protein and polypeptide toxins, stored and delivered into the prey through the stinging cells, the nematocytes. These include pore-forming cytolytic toxins such as well studied actinoporins. In this work, we have shown that the non-nematocystic paralytic toxins, hydralysins, from the green hydra Chlorohydra viridissima comprise a highly diverse group of beta-pore-forming proteins, distinct from other cnidarian toxins but similar in activity and structure to bacterial and fungal toxins. Functional characterization of hydralysins reveals that as soluble monomers they are rich in beta-structure, as revealed by far UV circular dichroism and computational analysis. Hydralysins bind erythrocyte membranes and form discrete pores with an internal diameter of approximately 1.2 nm. The cytolytic effect of hydralysin is cell type-selective, suggesting a specific receptor that is not a phospholipid or carbohydrate. Multiple sequence alignment reveals that hydralysins share a set of conserved sequence motifs with known pore-forming toxins such as aerolysin, epsilon-toxin, alpha-toxin, and LSL and that these sequence motifs are found in and around the poreforming domains of the toxins. The importance of these sequence motifs is revealed by the cloning, expression, and mutagenesis of three hydralysin isoforms that strongly differ in their hemolytic and paralytic activities. The correlation between the paralytic and cytolytic activities of hydralysin suggests that both are a consequence of receptor-mediated pore formation. Hydralysins and their homologues exemplify the wide distribution of beta-pore formers in biology and provide a useful model for the study of their molecular mode of action.

Amino Acid Motifs↗
PubMed1996

Transmission genetics of allorecognition in Hydractinia symbiolongicarpus (Cnidaria:Hydrozoa).

Allorecognition is ubiquitous, or nearly so, amongst colonial invertebrates. Despite the prominent role that such phenomena have played both in evolutionary theory and in on the origin of the vertebrate immune system, unambiguous data on the transmission genetics of fusibility (i.e., the ability of two individuals to fuse upon tissue contact) is lacking for any metazoan outside of the phylum Chordata. We have developed lines of the hydroid Hydractinia symbiolongicarpus (Phylum Cnidaria) inbred for fusibility and here report results of breeding experiments establishing that fusibility segregates as expected for a single locus with codominantly expressed alleles, with one shared allele producing a fusible phenotype. Surveys of fusibility in field populations and additional breeding experiments indicate the presence of an extensive allele series.

Alleles↗
PubMed2004

Crystallization and preliminary crystallographic analysis of a novel orange fluorescent protein from the Cnidaria tube anemone Cerianthus sp.

A novel orange fluorescent protein, with excitation and emission maxima at 548 and 565 nm, respectively, from the Cnidaria tube anemone Cerianthus sp. has been cloned and overexpressed in Escherichia coli. The orange fluorescent protein has been crystallized by the sitting-drop vapour-diffusion method at 290 K using polyethylene glycol 3350 as a precipitant. A complete set of diffraction data was collected to 2.0 A resolution at 100 K. The crystals belong to the space group R3, with hexagonal unit-cell parameters a = b = 216.947, c = 51.839 A. There are four protein molecules in the asymmetric unit, giving a Matthews coefficient of 2.3 A(3) Da(-1) and a solvent content of 47%.

Animals↗
PubMed2006

Invasion and persistence of a selfish gene in the Cnidaria.

BACKGROUND: Homing endonuclease genes (HEGs) are superfluous, but are capable of invading populations that mix alleles by biasing their inheritance patterns through gene conversion. One model suggests that their long-term persistence is achieved through recurrent invasion. This circumvents evolutionary degeneration, but requires reasonable rates of transfer between species to maintain purifying selection. Although HEGs are found in a variety of microbes, we found the previous discovery of this type of selfish genetic element in the mitochondria of a sea anemone surprising. METHODS/PRINCIPAL FINDINGS: We surveyed 29 species of Cnidaria for the presence of the COXI HEG. Statistical analyses provided evidence for HEG invasion. We also found that 96 individuals of Metridium senile, from five different locations in the UK, had identical HEG sequences. This lack of sequence divergence illustrates the stable nature of Anthozoan mitochondria. Our data suggests this HEG conforms to the recurrent invasion model of evolution. CONCLUSIONS: Ordinarily such low rates of HEG transfer would likely be insufficient to enable major invasion. However, the slow rate of Anthozoan mitochondrial change lengthens greatly the time to HEG degeneration: this significantly extends the periodicity of the HEG life-cycle. We suggest that a combination of very low substitution rates and rare transfers facilitated metazoan HEG invasion.

Animals↗
PubMed1986

Statolith formation in Cnidaria: effects of cadmium on Aurelia statoliths.

Statolith formation in Cnidaria was reviewed with an emphasis on Aurelia statoliths. The review provides information on the chemical composition, mechanisms of initiation of mineralization, and effects of environmental factors on Cnidarian statolith formation. Environmental factors discussed included modified sea water ingredients, X-irradiation, clinostat rotation, and petroleum oil ingredients. A detailed account of the effects of cadmium on mineralization and demineralization of Aurelia statoliths is given. Cadmium at dosages of 2 to 4 micromoles significantly reduces statolith numbers in developing ephyrae. At a dosage of 3 micromoles, cadmium accelerates statolith loss in unfed ephyrae studied at 4 and 8 days following ephyrae release from strobilae. Cadmium, therefore, is shown to reduce statolith numbers in developing ephyrae and to cause greater reduction of statolith numbers in unfed ephyrae after 4 and 8 days than occurred in controls. Supplementation of Cd(2+)-containing artificial sea water (ASW) with calcium (3X and 5X ASW calcium content) results in higher numbers of statoliths at day 4 as compared with cadmium-treated ephyrae. At 8 days only the 5X calcium supplemented ASW is effective in enhancing statolith numbers in Cd(2+)-treated ephyrae. These results suggest that cadmium competes in some manner with calcium at the mineralizing sites of Aurelia.

Animals↗
PubMed1990

Molecular and developmental biology of the Cnidaria--basic aspects and phylogenetic implications.

Cnidarians are generally considered to be the most primitive group of eumetazoans. They are therefore of considerable interest for comparative studies of metazoan development and evolution. The application of molecular techniques to cnidarians can provide important insights into developmental processes and phylogenetic relationships both within the phylum Cnidaria and among the eumetazoa. This paper reviews current knowledge of molecular and developmental biology of cinidarians with particular emphasis on tropical scleractinian corals and soft corals from the Great Barrier Reef region. Nucleotide sequencing of the histone gene cluster has unequivocally established that cnidarians are typical eumetazoans. Repeated sequence analysis has been applied to the staghorn corals, and implies a major divergence within this group, which corresponds with differences in sperm ultrastructure. Recent developmental studies of corals have indicated that some species have an unusual method of germ layer formation. Molecular events associated with this process, and with other important developmental stages, are currently under investigation. Other areas of current research interest, including targets for PCR-based investigations into cnidarian phylogeny, are highlighted.

Animals↗
PubMed2005

Complex colony-level organization of the deep-sea siphonophore Bargmannia elongata (Cnidaria, Hydrozoa) is directionally asymmetric and arises by the subdivision of pro-buds.

Siphonophores are free-swimming colonial hydrozoans (Cnidaria) composed of asexually produced multicellular zooids. These zooids, which are homologous to solitary animals, are functionally specialized and arranged in complex species-specific patterns. The coloniality of siphonophores provides an opportunity to study the major transitions in evolution that give rise to new levels of biological organization, but siphonophores are poorly known because they are fragile and live in the open ocean. The organization and development of the deep-sea siphonophore Bargmannia elongata is described here using specimens collected with a remotely operated underwater vehicle. Each bud gives rise to a precise, directionally asymmetric sequence of zooids through a stereotypical series of subdivisions, rather than to a single zooid as in most other hydrozoans. This initial description of development in a deep-sea siphonophore provides an example of how precise colony-level organization can arise, and illustrates that the morphological complexity of cnidarians is greater than is often assumed.

Animal Structures↗
PubMed1994

Mitochondrial DNA of the sea anemone, Metridium senile (Cnidaria): prokaryote-like genes for tRNA(f-Met) and small-subunit ribosomal RNA, and standard genetic code specificities for AGR and ATA codons.

The nucleotide sequence of a segment of the mitochondrial DNA (mtDNA) molecule of the sea anemone Metridium senile (phylum Cnidaria, class Anthozoa, order Actiniaria) has been determined, within which have been identified the genes for respiratory chain NADH dehydrogenase subunit 2 (ND2), the small-subunit rRNA (s-rRNA), cytochrome c oxidase subunit II (COII), ND4, ND6, cytochrome b (Cyt b), tRNA(f-Met), and the large-subunit rRNA (1-rRNA). The eight genes are arranged in the order given and are all transcribed from the same strand of the molecule. The overall order of the M. senile mt-genes differs from that of other metazoan mtDNAs. In M. senile mt-protein genes, AGA and AGG codons appear to have the standard genetic code specification of arginine, rather than serine as found for other invertebrate mt-genetic codes. Also, ATA has the standard genetic code specification of isoleucine. TGA occurs in three M. senile mt-protein genes and may specify tryptophan as in other metazoan, protozoan, and some fungal mt-genetic codes. The M. senile mt-rRNA(f-Met) gene has primary and secondary structure features closely resembling those of the Escherichia coli initiator tRNA, including standard dihydrouridine and T psi C loop sequences and a mismatch pair at the top of the aminoacyl stem. Determinations of the 5' and 3' end nucleotides of the M. senile mt-s-rRNAs indicated that these molecules have a homogenous size of 1,081 ntp, larger than any other known metazoan mt-s-rRNAs. Consistent with its larger size, the M. senile mt-s-rRNA can be folded into a secondary structure that more closely resembles that of the E. coli 16S rRNA than can any other metazoan mt-s-rRNA. These findings concerning M. senile mtDNA indicate that most of the unusual features regarding metazoan mt-genetic codes, rRNAs, and probably tRNAs developed after divergence of the Cnidarian line from the ancestral line common to other metazoa.

Amino Acid Sequence↗
PubMed2000

Mitochondrial DNA of Hydra attenuata (Cnidaria): a sequence that includes an end of one linear molecule and the genes for l-rRNA, tRNA(f-Met), tRNA(Trp), COII, and ATPase8.

The 3231-nucleotide-pair (ntp) sequence of one end of one of the two linear mitochondrial (mt) DNA molecules of Hydra attenuata (phylum Cnidaria, class Hydrozoa, order Anthomedusae) has been determined. This segment contains complete genes for tRNA(f-Met), l-rRNA, tRNA(Trp), subunit 2 of cytochrome c oxidase (COII), subunit 8 of ATP synthetase (ATPase8), and the 5' 136 ntp of ATPase6. These genes are arranged in the order given and are transcribed from the same strand of the molecule. As in two other cnidarians, the hexacorallian anthozoan Metridium senile and the octocorallian anthozoan Sarcophyton glaucum, the mt-genetic code of H. attenuata is near standard. The only modification appears to be that TGA specifies tryptophan rather than termination. Also as in M. senile and S. glaucum, the encoded H. attenuata mt-tRNA(f-Met) has primary and secondary structural features resembling those of Escherichia coli initiator tRNA(t-Met). As the encoded mt-tRNA(Trp) cannot be folded into a totally orthodox secondary structure, two alternative forms are suggested. The encoded H. attenuata mt-l-rRNA is 1738 nt, which is 451 nt shorter than the M. senile mt-l-rRNA. Comparisons of secondary structure models of these two mt-l-rRNAs indicate that most of the size difference results from loss of nucleotides in the H. attenuata molecule at a minimum of 46 locations, which includes elimination of six distinct helical elements.

Adenosine Triphosphatases↗
PubMed2006

The evolution of colony-level development in the Siphonophora (Cnidaria:Hydrozoa).

Evolutionary developmental biology has focused almost exclusively on multicellular organisms, but there are other relevant levels of biological organization that have remained largely neglected. Animal colonies are made up of multiple physiologically integrated and genetically identical units called zooids that are each homologous to solitary, free-living animals. Siphonophores, a group of pelagic hydrozoans (Cnidaria), have the most complex colony-level organization of all animals. Here the colony-level development of five siphonophore species, strategically sampled across the siphonophore phylogeny, is described from specimens collected using deep-sea submersibles and by self-contained underwater breathing apparatus diving. These species include three cystonects, Bathyphysa sibogae, Rhizophysa filiformis, and Rhizophysa eysenhardti, and two "physonects", Agalma elegans and Nanomia bijuga. These data, together with previous findings, are analyzed in a phylogenetic framework to reconstruct key features of the history of colony-level organization and development in the Siphonophora. It is shown that gonodendra and gastrozooids of the examined cystonects arise as independent buds directly on the stem, whereas probud subdivision (the origin of feeding, reproductive, and other zooids from a single bud) is a synapomorphy of the Codonophora. The origin of probud subdivision is associated with the origin of cormidia as integrated units of colony organization, and may have allowed for greater morphological and ecological diversification in the Codonophora relative to the Cystonectae. It is also found that symmetry is labile in siphonophores, with multiple gains and/or losses of directional asymmetry in the group. This descriptive work will enable future mechanistic and molecular studies of colony-level development in the siphonophores.

Animals↗