Marine Hydrozoan Research Articles

Ultrastructural Localization of RFamide-like Peptides in Neuronal Dense-Cored Vesicles of a Cnidarian Planula Larva

The location of Arg-Phe-amide (RFamide)-like peptides in dense-cored vesicles in neurons of the planula larva of the marine hydrozoan Pennaria tiarella was shown using immunogold electron microscopy. Expression of the peptide was detected as early as 16 h after fertilization. Gold-labeled dense-cored vesicles ranging from 80 nm to 140 nm in diameter were found in both cell bodies and neurites of ganglion cells (non-ciliated bipolar and multipolar neurons found at the base of the ectoderm just above the mesoglea) located in the aboral (anterior) and middle regions of the planulae. Within the neurites, the labeled dense-cored vesicles were found in distinct clusters all along their lengths in close association with the cell membranes, a distribution which suggests that release of the peptide in planulae probably does not occur at specialized synaptic sites. Labeled cells also contained unlabeled dense-cored vesicles, unlabeled clear vesicles (60 nm to 100 nm in diameter), and unlabeled electron-dense droplets (100 nm to 240 nm in diameter). Localization of RFamide peptides to dense-cored vesicles of specific neurons in early planulae is significant because of growing evidence on the role of these substances in morphogenesis. Additional key words: neuropeptide, neural development, hydrozoans, Pennaria tiarella Peptides structurally related to the neuropeptide Phe-Met-Arg-Phe-amide (FMRFamide) are abundant in the nervous systems of cnidarians (Grimmelikhuijzen 1984; Grimmelikhuijzen & Graff 1985; Grimmelikhuijzen et al. 1992; Martin 1992; Westfall & Grimmelikhuijzen 1993). When antiserum to FMRFamide or its carboxyterminal fragment RFamide is applied to cnidarians, subsets of nerve cells are identified (Grimmelikhuijzen 1984). The exact subcellular location of these immunoreactive substances within neurons has been shown only in adults of a few species of cnidarians. In the freshwater hydrozoan Hydra littoralis, RFamide was found in dense-cored vesicles in both neurites and nerve terminals (Koizumi et al. 1989); in the sea anemone Anthopleura elegantissima, RFamide activity was seen in four different types of neuronal vesicles (opaque vesicles, heterogranular vesicles, dense-cored vesicles, and light-cored vesicles) in the tentacle plexus (Westfall & Grimmelikhuijzen 1993); and in the hydromedusa Aglantha digitale, FMRFamide-like immunoreactivity was found in large dense-cored vesicles (Singla & Mackie 1991). That at least some cnidarian larvae contain RFama To whom correspondence should be addressed. ide-like material was first demonstrated in planulae of the hydroid Pennaria tiarella (= Halocordyle disticha) (Martin 1992). When antiserum to RFamide was applied to 48and 72-h planulae and visualized with FITC (fluorescein isothiocyanate), some of the ganglion cells in the aboral (anterior) and middle regions and a few ganglion cells in the oral (posterior) regions exhibited immunoactivity. Ganglion cells (also referred to as ganglionic cells in previous publications) are non-ciliated bipolar and multipolar neurons found at the base of the ectoderm just above the mesoglea. A very small number of sensory neurons in the aboral end of planulae also expressed RFamide; however, the great majority of the stained neurons were ganglion cells. Not determined, however, was the subcellular location of the neuropeptide in the planula and how early in development expression of RFamide began. This study uses the superior sensitivity of immunogold to demonstrate that RFamide-like material is located in non-synaptic dense-cored vesicles of cell bodies and processes of ganglion cells of the planula of Pennaria tiarella. The immunogold method reveals subcellular localization of neuropeptide and also detects lower levels of neuropeptide than does the previously used FITC method. These results are the first This content downloaded from 157.55.39.189 on Sun, 12 Mar 2017 19:06:04 UTC All use subject to http://about.jstor.org/terms

Cell adhesion to extracellular matrix is different in marine hydrozoans compared with vertebrates.

Extracellular matrices (ECMs) of phylogenetically very distant organisms were tested for their ability to support cell adhesion, spreading and DNA replication in reciprocal xenograft adhesion tests. Mechanically dissociated cells of the medusa Podocoryne carnea (Cnidaria, Hydrozoa) were seeded on ECMs of polyps and medusa, and on several ECM glycoproteins or entire ECMs from vertebrates. In reciprocal experiments, cells from different vertebrate cell-lines were seeded on ECMs of polyps, medusae and also on electrophoresed and blotted extracts of both types of ECMs. The results demonstrate that medusa cells adhere and spread on polyp and medusa ECMs but do not recognize vertebrate ECMs or purified ECM glycoproteins. Vertebrate cells in contrast adhere, spread and proliferate on ECMs of polyps and medusae. The number of attached cells depends on the cell type, the type of ECM and, in certain cases, on the stage of the cell cycle. Cell adhesion experiments with pretreated ECMs of polyps and medusae, e.g. oxidation of carbohydrate residues with sodium-metaperiodate, or blocking of certain carbohydrate moieties with the lectin wheat germ agglutinin or a carbohydrate-specific monoclonal antibody, demonstrate that ECM carbohydrates are more important for cell-ECM interactions of medusa cells than for vertebrate cells. Furthermore, the experiments indicate that polyp and medusa ECMs contain different components which strongly modulate adhesion, spreading and DNA replication of vertebrate cells.

Cytoskeletal elements in migrating and tentacle-integrated nematocytes of a marine hydrozoan

Actively migrating nematocytes of the marine polyp Stauridiosarsia producta are converted into completely immotile cells as soon as they become integrated in the ectodermal tissue of the tentacles. Immunocytochemical and electron microscopical methods revealed that cytoskeletal elements composed of actin, tubulin, centrin and a still unidentified protein are interwoven within the complete cell. While the organization of the sensory pole of the nematocyte, containing the cnidocil complex, the pseudovillar system and the distal half of a microtubular basket surrounding the nematocyst, is not affected by the transition from a motile to an immotile cell, the cytoskeletal elements in the basal portion of the cell are re-organized. Thus, the basolateral cytoplasm of migrating cells contains less organized microtubular arrays and bundles of about 10 nm-thick filaments. In the tentacle-integrated state, the 10-nm filaments are concentrated within a stalk-like foot which is stabilized by some rigid microtubular arrays derived from the microtubular basket. By elongation of the microtubular basket towards the cellular basis, the nematocyst becomes indirectly anchored at the mesoglea. As indicated by pharmacological treatments, the stiffness of the stalk depends on its microtubular content only.

The analysis of paternity and maternity in the marine hydrozoan Hydractinia symbiolongicarpus using randomly amplified polymorphic DNA (RAPD) markers.

For organisms in which direct observation of mating and subsequent dispersal of offspring and relatives is impossible, patterns of reproductive success and genealogical relationship can only be established using genetic markers. The ideal genetic assay would (1) employ highly polymorphic genetic markers for distinguishing among individuals; (2) use little tissue for analysing early life-history stages; and (3) require minimal investment in time and money for population level studies. From this perspective, DNA polymorphisms revealed by PCR amplification using random ten-base primers [Randomly Amplified Polymorphic DNA (PCR-RAPD) or Arbitrarily Primed DNA (AP-PCR)] have great potential. However, the evidence that RAPD/AP markers are both heritable and can be repeatably amplified remains controversial. This study characterizes patterns of inheritance and polymorphism of RAPD markers in the free-spawning, colonial marine hydrozoan Hydractinia symbiolongicarpus. In all cases, the amplification products were identical among extractions from the same clone. Of 56 primers screened, 13 had sufficient polymorphism and scoreability for an analysis of parentage and higher-order genetic relationships in three matings. These primers generated 156 unique amplification products (putative loci), of which 133 were polymorphic. All but four of these loci were inherited as dominant mendelian markers. Our study suggests that the presence of a marker represents a single allele at a locus; however, what appear to be single null alleles may actually comprise several segregating alleles. When the identity of neither parent was known a priori, inclusion (unique markers present in offspring and only one of the potential parents) proved to be more efficient than exclusion for assigning offspring to parents. The most powerful approach, however, was cluster analysis of all presence/absence information for the marker bands. Clustering avoided the pitfalls caused by the appearance of occasional nonparental bands, and constructed a hierarchical framework that correctly reflected all genealogical relationships.

Cytophysiology of growth pulsations in hydroid polyps

AbstractCell orientation and intercellular changes accompanying growth pulsations (GP) have been studied in the marine hydroids Obelia longissima, O. loveni, and Dynamena pumila with the use of time‐lapse filming, mechanography, optical microscopy, and electron microscopy. The extension phase of the GP was correlated with an increase in cell volume and the rotation of cells to a transverse orientation. Tip cells return to an oblique orientation during the retraction phase via a rapid (about 1 μm/second) distalward sliding of external cell poles. In most samples, a proximodistal wave of transversad cell rotations was observed within a period of 30–90 μm/minutes. In contrast, return to the oblique orientation is almost synchronous. The extension GP phase is correlated with extensive cell vacuolization and the retraction phase with fusion of these vacuoles into elongated channels opening into external space.The extension phase was stabilized in hypotonic medium, isotonic medium with increased NaCl concentration, and by ionic transport inhibitors (which increase cytoplasmic concentration of Na+ and Cl−). GP are arrested in the retraction phase in hypertonic medium, isotonic medium with decreased Na+ and Cl− concentration, and by inhibitors whose decreasing cytoplasmic concentrations of Na+ and Cl− arrest GP in the retraction phase. These data point out the participation of osmotic mechanisms in the regulation of GP.

A MORPHOLOGICAL EXAMINATION OF GASTRULATION IN A MARINE ATHECATE HYDROZOAN

The early embryonic development of the marine hydrozoan Halocordyl disticha is examined via light histology and transmission electron microscopy. Particular emphasis is devoted to the gastrula and the mode of gastrulation. Cleavage in Halocordyl disticha is irregular, total, and asynchronous resulting in the production of stereoblastulae. Each stereoblastula forms a blastopore at the future posterior end of the larva and gastrulates via invagination to produce a lecithotrophic planula larva. During gastrulation spherical surface cells radially migrate toward the blastopore, become cuboidal-shaped in the region of the pore, and disappear to the interior of the embryo. Gastrulation requires 2 h to complete, during which time the ectoderm becomes separated from the endoderm by a mesoglea, interstitial cells arise in the central endoderm, and the embryo elongates to form a planula larva. This study presents the first documented example of invagination in the Hydrozoa.

Catecholamines induce metamorphosis in the hydrozoan Halocordyle disticha but not in Hydractinia echinata

Planula larvae of the marine hydroids Halocordyle disticha and Hydractinia echinata were treated with the catecholamines epinephrine, norepinephrine and dopamine, as well as with certain of their precursors and agonists. Norepinephrine, L-dopa, dopamine and the dopamine agonist ADTN at concentrations ranging from 0.1 to 0.001 mM induced metamorphosis within 24 h in Halocordyle disticha, with no observable morphogenetic abnormalities. Epinephrine, the adrenergic agonists phenylephrine, isoproterenol and methoxyamine, and the catecholamine precursors phenylalanine and tyrosine were found not to induce metamorphosis at the concentrations employed. None of the compounds was effective in inducing metamorphosis in Hydractinia echinata. A model is presented for neural control of metamorphosis in Halocordyle disticha.

A SCANNING ELECTRON MICROSCOPIC STUDY OF EMBRYONIC DEVELOPMENT OF A MARINE HYDROZOAN

An indepth three-dimensional investigation examined the surface morphological changes associated with the development of a typical marine hydrozoan early cleavage embryo into a mature planula larva. During hydrozoan embryogenesis the arrangement and distribution of surface microvilli change; cilia of some epitheliomuscle cells appear before embryos gastrulate; and the embryo undergoes dramatic changes in body shape. Early cleaving embryos are bizarre in morphology, however, by the end of late cleavage the embryos have rounded to form a sphere. Gastrulation is characterized by the appearance of a blastopore at the future posterior end of the planula and by the migration of cells over the margins of the blastopore to the inside of the embryo. The product of gastrulation is a young planula which elongates and decreases in overall diameter to form a mature planula that eventually attaches via its anterior end to a substrate and undergoes metamorphosis.

BIOLOGY OF HYDRACTINIID HYDROIDS. 4. ULTRASTRUCTURE OF THE PLANULA OFHYDRACTINIA ECHINATA

The fine structure of the ectodermal surface of the planula larva of Hydractinia echinata is described and the spatial distribution of cell types quantified. The larval ectoderm contains five cell types: nematocytes, gland cells, epitheliomuscular cells, neurosensory cells, and nerve cells. Nematocytes (atrichous isorhizas and desmonemes) and neurosensory cells are clustered at the tapered posterior end of the larvae. Mucous cells occur over the surface of the planula, but are particularly common at the anterior end. The larva is similar to others described from marine hydroids, except that (a) gland cells display a ring of microvilli emerging from a cavity encircling the cilium and (b) nerve cells appear to lack a cilium.

Acyclic polyhalogenated monoterpenes from four marine hydroids

Four polyhalogenomonoterpenes have been isolated from four species of marine hydroids. Their biological role is briefly discussed.

The Ecology of Marine Hydroids and Effects of Environmental factors: A Review

Abstract. The history of the study of hydroid ecology is briefly outlined, pointing out the major methodological innovations which have contributed to the development of ecological research in the last thirty years. The influence of the major ecological factors on hydroid ecology and biology is synthesized, taking into account: substratum, water movement, light, salinity, sedimentation, exposure to air, temperature, food availability and pollution. Besides affecting the species composition of the hydroid community, these factors also influence the morphology and general biology of the individual species. The adaptations and reactions of hydroids to different intensities of the various environmental factors and to their combinations are reported.

A fine structural study of metamorphosis of the hydrozoan Mitrocomella polydiademata.

This report is a comprehensive fine structural analysis of the morphological changes occurring during metamorphosis of the marine hydrozoan Mitrocomella polydiademata. Five stages are recognized during metamorphosis: planulae just prior to settlement, ball and filiform stages, immature polyps, and primary feeding polyps. Settlement and metamorphosis of cnidarian planulae involve such changes as ciliary arrest, discharge of nematocytes, secretion of glandular cells, differentiation of cells, and changes in cell and body shape.

Elimination of the interstitial cells in the planula larva of the marine hydrozoan Pennaria tiarella

AbstractTreatment of 8‐hour embryos of the marine hydrozoan Pennaria tiarella with colchicine results in the complete elimination of interstitial cells, nematoblasts, and sensory‐motor‐interneurons. Depletion of these cells is mediated through the action of acid phosphatase‐positive autophagic vacuoles.Larvae depleted of interstitial cells acquire normal polarity although body form is somewhat modified. This modification appears to be due to a loss in cell volume normally provided by the interstitial cells. These larvae remain without interstitial cells throughout larval life. This finding demonstrates that the remaining larval epithelial cells are not totipotent and therefore lack the plasticity to redifferentiate into interstitial cells. The fact that epitheliomuscle cells, mucous cells, neurosensory cells, and gastrodermal cells all differentiate normally after elimination of the interstitial cells suggests that the interstitial cells are not involved in induction of the epithelial cell types. Furthermore, the histological organization of the presumptive epithelial cells appears in no way to be affected by the interstitial cells. In the absence of these cells the remaining cells of the embryo become organized into a distinct epidermis and gastrodermis separated by a mesoglea. Larvae devoid of interstitial cells and their derivatives fail to metamorphose.The specific mechanism by which colchicine eliminates the interstitial cells is investigated. Embryos treated with vinblastine sulfate and podophyllotoxin, both known microtubule inhibitors, exhibit the same autophagic elimination of the interstitial cells, the nematoblasts, and the sensory‐motor‐interneurons as that seen in embryos treated with colchicine. Embryos treated with lumicolchicine are identical morphologically to control planulae of comparable age and contain interstitial cells, nematoblasts, and sensory‐motor‐interneurons. These results demonstrate that the principle action of colchicine in Pennaria is microtubule related.

THE ORIGIN OF THE NERVOUS SYSTEM INPENNARIA TIARELLA, AS REVEALED BY TREATMENT WITH COLCHICINE

Treatment of 8-h embryos of the marine hydrozoan Pennaria tiarella with colchicine for 2 h eliminates interstitial cells, nematoblasts, and ganglionic cells. Comparisons of interstitial-cell-less and control planulae of Pennaria by TEM and light microscopy suggest a dual origin of the nervous system in Pennaria. Ganglionic cells are shown to be derived exclusively from endodermally-derived interstitial cells, whereas neurosensory cells are derived from cells of the ectodermal epithelium, probably from the epitheliomuscle cells. This investigation supports the idea that ganglionic cells and neurosensory cells can differentiate not only from different stem cells but also from different germ layers.

The biology of colonial hydroids. II. The morphology and ultrastructure of the medusa of Eirene viridula (Thecata-Leptomedusa: Campanulinidae)

The free-swimming medusae of Eirene viridula are typical marine hydroids, with distinct subdivisions into body regions, which were studied by comparison of light and electron microscopy. Particular attention is given to the epithelio-muscular and digestive muscle cells. The epidermis — apart from a few nerve cells and cnidocytes-consists of epitheliomuscular cells. At their bases these cells form a musculature and at the apex many secretory vesicles. In the velum, large expansions of the intercellular space are found. The gastrodermis — apart from the mucous and zymogen cells in the manubrium — consists of digestive muscle cells, the structure of which corresponds in principle to that of the epitheliomuscular cells. In its apex, this type of cells contains both “normal” coated vesicles and discoidal coated vesicles. In the solid tentacles, the digestive muscle cells form a turgescent vesicular tissue. The central nervous system consists of the exumbrellar, subumbrellar, and gastrodermal nerve rings. They are composed of ganglion cells, their processes, and intraepithelial flagella. The static organs are purely ectodermal statocysts which have only one lithocyte and only one sensory cell.

The absence of electrically demonstrable polarizing factors in Hydra.

AbstractVarious investigators have shown that in the marine hydroids, Tubularia, Obelia, Eudendrium, and Pennaria, regeneration and polarity is affected by an electrical field applied parallel to the regenerate. Using electrical currents up to the physiological limits for Hydra, no relation between electrical current and regeneration rate or polarity could be demonstrated. This is in spite of the fact that adult Hydra are normally electrically polarized with the distal end approximately–18 mV relative to the proximal end of the animal. When the electrophoretic mobility and isoelectric point of cells from distal, central and proximal thirds of Hydra were measured, a significant difference was found between cells of the two cell layers but not between cells of the three body thirds. These results are discussed in relation to Hydra growth factors described by various other authors.

Hydroid generation and developmental history ofEucheilota maculata (Thecata — Leptomedusae). With a contribution to the methods of culturing marine hydroids

Polyps and medusae differ in regard to habitats, evolution, and morphological structures. In order to replace the former taxonomic systems which deal with polyp and medusa generations separately, by a single valid classification including both generations, knowledge of all essential life history phases is necessary. Modern methods of culturing marine hydroids are outlined briefly. Successful culturing provides the means to link formerly unidentified polyps or medusae with one another. The present paper is concerned with the hydroidEucheilota maculata Hartlaub, the medusa of which is common in the southern North Sea. The polyps formerly unknown have been reared from fertilized eggs of the medusae. They were raised to full size, formed colonies, and produced gonangia and medusae. Thus the morphology of the single polyp, the polyp colony, and of the young medusa could be investigated in detail. The nematocyst equipment of the two generations and of all developmental stages is described as well as the number of chromosomes. The systematic position of the genusEucheilota is discussed and the diagnosis of the speciesE. maculata, including the two generations, given.

Hydroids from Louisiana and Texas, with Remarks on the Pleistocene Biogeography of the Western Gulf of Mexico

Few parts of the world offer a more absolute blank to the zoogeographer of marine hydroids than the Gulf coast of Texas. Although the marine biology of the western Gulf of Mexico is probably somewhat better known than that of western Australia or Ellesmere Island, it is a fact that systematic hydroid collecting has never been done in Texas, and the recent monograph of Fraser ('44) lists only three species from that State. In the collection of the Woods Hole Oceanographic Institution, the hydroids of which are now in my hands, there are 57 samples from 20 navigation buoys in Texas waters, but most of these samples contain nothing but Obelia dichotoma (Linnaeus), and the list of ten species is so small that separate publication would not be justified. An additional 25 samples from Texas and Louisiana, recently received from Joel W. Hedgpeth, have proved so interesting, however, that an account of the whole material seems warranted. Permission to use the Texas records from the Woods Hole collection in advance of the full report has generously been granted by Louis W. Hutchins.