Adult Medusa Research Articles

The germ line and somatic stem cell gene Cniwi in the jellyfish Podocoryne carnea.

In most animal phyla from insects to mammals, there is a clear division of somatic and germ line cells. This is however not the case in plants and some animal phyla including tunicates, flatworms and the basal phylum Cnidaria, where germ stem cells arise de novo from somatic cells. Piwi-like genes represent essential stem cell genes in diverse multicellular organisms. The cnidarian Piwihomolog Cniwiwas cloned from Podocoryne carnea, a hydrozoan with a full life cycle. CniwiRNA is present in all developmental stages with highest levels in the egg and the medusa. In the adult medusa, Cniwi expression is prominent in the gonads where it likely functions as a germ stem cell gene. The gene is also expressed, albeit at low levels, in differentiated somatic cells like the striated muscle of the medusa. Isolated striated muscle cells can be induced to transdifferentiate into smooth muscle cells which proliferate and differentiate into nerve cells. Cniwi expression is upregulated transiently after induction of transdifferentiation and again when the emerging smooth muscle cells proliferate and differentiate. The continuous low-level expression of an inducible stem cell gene in differentiated somatic cells may underlie the ability to form medusa buds from polyp cells and explain the extraordinary transdifferentation and regeneration potential of Podocoryne carnea.

Morphological and ultrastructural analysis of Turritopsis nutricula during life cycle reversal

The hydrozoa life cycle is characterized, in normal conditions, by the alternation of a post-larval benthic polyp and an adult pelagic medusa; however, some species of Hydrozoa react to environmental stress by reverting their life cycle: i.e. an adult medusa goes back to the juvenile stage of polyp. This very uncommon life cycle could be considered as some sort of inverted metamorphosis. A morphological study of different stages during the reverted life cycle of Turritopsis nutricula led to the characterization of four different stages: healthy medusa, unhealthy medusa, four-leaf clover and cyst. The ultrastructural study of the cellular modifications (during the life cycle reversion of T. nutricula) showed the presence of both degenerative and apoptotic processes. Degeneration was prevalent during the unhealthy medusa and four-leaf clover stages, while the apoptotic rate was higher during the healthy medusa and cyst stages. The significant presence of degenerative and apoptotic processes could be related to the occurrence of a sort of metamorphosis when an adult medusa transforms itself into a polyp.

Evolutionary aspects of developmentally regulated helix-loop-helix transcription factors in striated muscle of jellyfish

The function of basic helix-loop-helix (bHLH) proteins in cell differentiation was shown to be conserved from Drosophila to vertebrates, exemplified by the function of MyoD in striated muscle differentiation. In phylogeny striated muscle tissue appears first in jellyfish and the question of its evolutionary position is controversially discussed. For this reason we have studied the developmental role of myogenic bHLH genes in medusa development. Based on their dimerization ability, four genes of the bHLH family of transcription factors were isolated from the hydrozoan jellyfish Podocoryne carnea. While the proteins Id and Ash group with cognate family members from bilaterians, Net-like and JellyD1 could not be unequivocally classified. Id is expressed during the medusa budding process and in the adult medusa, Ash and Net-like are expressed in all life cycle stages from egg to adult medusa and JellyD1 is expressed in the blastula and gastrula stages, the planula larva, and in late medusa bud stages. The dimerization specificity, the expression pattern, and the conservation of two residues specific for a MyoD bHLH domain suggest that JellyD1 is related to an ancestral MyoD gene. Id, Net-like, and JellyD1 are either expressed in the entocodon or its derived tissues, the striated and smooth muscle of the bell. These findings strengthen the hypothesis that the entocodon is a mesoderm-like structure and that the common ancestor of Cnidaria and Bilateria was more complex in cell-type architecture and body organization than commonly thought.

The life cycle of <i>Halimedusa typus</i>, with discussion of other species closely related to the family Halimedusidae (Hydrozoa, Capitata, Anthomedusae)

The little-known Anthomedusa Halimedusa typus has been collected from several locations in California, Oregon, and British Columbia on the Pacific coast of the United States. The adult medusa is redescribed based on new observations of living material and is found to have capitate tentacles. Polyps of H. typus were raised several times after spawning field-collected medusae in the laboratory; the cultures on one occasion lived for more than a year. The capitate polyp is solitary and very tiny, emerging from a basal perisarc measuring 200-300 µm in diameter. One cultured polyp produced a medusa, which is described. The taxonomic positions of several other morphologically-similar Anthomedusae in the Capitata are compared and discussed here. Tiaricodon coeruleus and Urashimea globosa are moved from the Polyorchidae to the Halimedusidae, and the similarity of Boeromedusa auricogonia (Boeromedusidae) to all of these medusae and to the genera Polyorchis, Scrippsia and Spirocodon of the family Polyorchidae is considered. The group of species under consideration is basically restricted to the Pacific Ocean, except for T. coeruleus and U. globosa, which have also been collected in the south Atlantic and south Atlantic/Antarctic. It is noted that medusae of the Halimedusidae are typically found quiescent near the surface, whereas those of the Polyorchidae either rest on the bottom or must continue pulsating to stay up in the water column, indicating a basic underlying difference in buoyancy and resultant behavior between the medusae in these two families.

The life cycle of Hebella furax (Cnidaria: Hydrozoa): a link between a lafoeid hydroid and a laodiceid medusa

The adult medusa of a species of the hydroid genus Hebella Allman, 1888 (family Lafoeidae), with a metagenetic life cycle, is described for the first time. Hebella furax Millard, 1957 is epizoic on other hydroids and releases medusae with four radial canals and three marginal bulbs with tentacles. Adult medusae cultured in the laboratory attained 11 mm in diameter, had 8–11 radial canals, and up to 37 marginal tentacles. Cordyli were present between the tentacles, a characteristic feature of the superfamily Laodiceoidea. The pattern of branching of the radial canals indicates that adult medusae of H.furax should be referred to the genus Toxorchis, possibly to T. kellneri Mayer, 1910.

The HOX-like gene Cnox2-Pc is expressed at the anterior region in all life cycle stages of the jellyfish Podocoryne carnea.

The marine jellyfish Podocoryne carnea (Cnidaria, Hydrozoa) has a metagenic life cycle consisting of a larva, a colonial polyp and a free-swimming jellyfish (medusa). To study the function of HOX genes in primitive diploblastic animals we screened a library of P. carnea cDNA using PCR primers derived from the most conserved regions in helix 1 and helix 3 of the homeobox. A novel gene, Cnox2-Pc, has been isolated and characterized. Cnox2-Pc is a HOX cluster-like gene, and its homeodomain shows similarity to the Deformed subfamily of HOM-C/HOX genes. In situ hybridization revealed that Cnox2-Pc is expressed in the anterior region of the larva, the polyp head, and the most apical ectoderm of the differentiating bud during medusa development. In adult medusa expression is restricted to the gastrovascular entoderm. The results suggest that Cnox2-Pc is involved in establishment of an anterior-posterior axis during development in primitive metazoans.

A toxin homology domain in an astacin-like metalloproteinase of the jellyfish Podocoryne carnea with a dual role in digestion and development.

Metalloproteinases of the astacin family such as tolloid play major roles in animal morphogenesis. Cnidarians are thought to be evolutionary simple organisms and, therefore, a metalloproteinase from the marine hydrozoan Podocoryne carnea was analysed to evaluate the role of this conserved gene familiy at the base of animal evolution. Surprisingly, the proteinase domain of Podocornyne PMP1 is more similar to human meprin than to HMP1 from another hydrozoan, the freshwater polyp Hydra vulgaris. However, PMP1 and HMP1 both contain a small C-terminal domain with six cysteines that distinguishes them from other astacin-like molecules. Similar domains have been described only recently from sea anemone toxins specific for potassium channels. This toxin homology (Tox1) domain is clearly distinct from epidermal growth factor (EGF)-like domains or other cysteine-rich modules and terminates with the characteristic pattern CXXXCXXC with three out of six cysteines in the last eight residues of the protein. PMP1 is transiently expressed at various sites of morphogenetic activity during medusa bud development. In the adult medusa, however, expression is concentrated to the manubrium, the feeding organ, where the PMP1 gene is highly induced upon feeding. These disparate expression patterns suggest a dual role of PMP1 comparable to tolloid in development and, like astacin in the crayfish, also for food digestion. The Tox1 domain of PMP1 could serve as a toxin to keep the pray paralysed after ingestion, but as a sequence module such Tox1 domains with six cysteines are neither restricted to cnidarians nor to toxins.

The life cycle of Hydrichthys mirus (Cnidaria: Hydrozoa: Anthomedusae: Pandeidae)

The previously unknown life cycle of the parasitic hydroid Hydrichthys mirus is described. The adult medusa has 5–6 tentacles and could be referred to Leuckartiara. Another species of Hydrichthys has previously been shown to have a Stomotoca-like medusa, characterized by the possession of two tentacles. It is proposed that Hydrichthys originated from the Leuckartiara lineage and that, through paedomorphosis in at least one species, the medusa retained the two-tentacle state of the newly-released medusa of all pandeids, thus becoming referable to Stomotoca. It is suggested that Stomotoca has hitherto constituted a polyphyletic taxon, embracing parallel lineages of pandeids, each retaining juvenile features. An additional genus, Larsonia, is introduced to accommodate species with Stomotoca-like medusae and Hydrichthys-like hydroids.

Composition of gelatin from developmental stages of the sea nettle, chrysaora quinquecirrha

Abstract 1. 1. Gelatin, extracted by autoclaving animals after removing free amino acids with 80% ethanol, ranges from 43% of total protein in the scyphistoma to 80% in the adult medusa. 2. 2. Glutamic acid is predominant in gelatin from the scyphistoma, whereas adult gelatin is more typical of collagens from other cnidarians. 3. 3. Glycine, hydroxylysine and hydroxyproline are all lower than in other cnidarian collagens, suggesting a low degree of cross-linking in this species.

Growth stages of the medusa of Proboscidactyla flavicirrata Brandt, 1835 (Hydrozoa; Limnomedusae)

The growth stages of laboratory-reared medusae of Proboscidactyla flavicirrata Brandt, 1835 which link the polyp with the adult medusa are described. Eggs of female medusae were visible in the gonads after 9 weeks of development. Variability in development of radial canals and gonads was infrequent and possibly the result of poor culture conditions. Nematocysts tended to increase in size as the medusae grew. Medusae were maintained in the laboratory for 121 days.

The ontogeny of swimming behavior in the scyphozoan, Aurelia aurita. I. Electrophysiological analysis.

1. Electrical correlates of behavioral activity were observed in the lip and tentacles of the polyp, but none were detected during column contraction. The tentacles are the most electrically active tissue, and the potentials are conducted along the length of the tentacle, but conduction to other parts of the animal were not observed. 2. Although the tentacles of the polyp and the rhopalia of the medusa are probably homologous, the development of pacemaker activity during strobilation is not a smooth transition from tentacle contraction potentials (TCPs) to marginal ganglion potentials (MGPs). This result indicates that each pacemaker activity develops de novo. 3. Two types of behavior were observed in the polyp: local responses, and coordinated activity which involved integrated responses in several body parts. The coordinated responses indicate that neurological coordination can take place in the polyp. Furthermore, feeding and spasm in the ephyra are similar to feeding and the protective response in the polyp. This similarity suggests that both coordinated responses in the polyp are coordinated by interneural facilitation in the diffuse nerve net (DNN) as in the ephyra. 4. Swimming in the ephyra is a medusoid behavior but feeding and spasm are coordinated by the DNN and are polypoid responses. Therefore, the ephyra is a mixture of polypoid and medusoid behaviors. As the ephyra matures into an adult medusa both polypoid responses are lost, but the DNN remains to modulate pacemaker output and control marginal tentacle contractions. As development proceeds from polyp, to ephyra, to medusa, each subsequent stage acquires some new behavior while retaining some aspect from the previous stage.

The ontogeny of swimming behavior in the scyphozoan, Aurelia aurita. II. The effects of ions and drugs.

1. The responses of Aurelia medusae to pharmacological agents and ionic variation were classified into four response types: Type I, no response; Type II, inhibition of pacemaker activity; Type III, inhibition of both pacemakers and swimming muscles; and Type IV, increase in pacemaker output. 2. The swimming pacemakers of Aurelia medusae become hyperactive in Mg+2-free solutions (Type IV). This response appears to be general in swimming scyphozoa. 3. The response pattern to pharmacologically-active compounds indicates that the coelenterate neuromuscular system is quite different than those in other phyla. In fact, the response spectrum is not consistent within the Cnidaria. 4. Similarly, the responses of adult medusae to ionic variation show no consistent pattern within various scyphomedusae. 5. Test solutions from each response type established with medusae were selected and tested on the scyphistoma and strobila stages. The comparison of the responses to the test solutions between the medusa, scyphistoma, and strobila showed that the neuromuscular systems are physiologically different. The strobila, specificially the ephyra, is a mixture of both polypoid and medusoid response types. The strobila, therefore, is physiologically an intermediate stage in the development of the adult medusa.

Polyp and medusa of Dipurena bicircella n. sp. (Hydrozoa: Corynidae) from Northern California

The polyp and medusa of Dipurena bicircella n. sp., a metagenic hydrozoan from Northern California, USA, is described. The arrangement of capitate tentacles of the polyp, in two alternating cycles or circlets, is unique to the genus Dipurena as well as to the family Corynidae. Medusae released in the laboratory attained sexual maturity in 2 weeks. The adult medusa can be distinguished from other medusae of the genus by means of 2 gonad rings, a slight terminal nematocyst cluster on each tentacle, and a relatively small size (about 2 mm in bell height). The polyp was not found in association with sponges, as is the case with some of the other polyps of the genus Dipurena. The medusa is not yet known from the plankton.

The life cycle ofClytia attenuata (calyptoblastea: Campanulariidae)

The life cycle of the hydroidClytia attenuata (Calkins) (Calyptoblastea: Campanulariidae) has been completed in the laboratory including development of the medusa, previously described asPhialidium lomaeTorrey (Leptomedusae: Campanulariidae). Under laboratory conditions, the hydroid exhibits some morphological variation. Characteristic branching of the hydroid occurs at temperatures between 17° to 19°C. At 13° to 15°C the colonies are unbranched and cannot be distinguished fromClytia cylindricaL. Agassiz. Young medusae are similar to other young species ofPhialidium. Development to the adult form requires 25 to 30 days at 17° to 24°C. The adult medusae are 6 to 10 mm in diameter, watch-glass shaped, and have 20 to 28 tentacles. Based on the adult medusa,Clytia attenuata is maintained as a valid species.