Hydrozoa

Voltage sensitivity of voltage-gated potassium channels (VKCs) is a primary factor in shaping action potentials in excitable cells. Variation in the amino acid sequence of the channel proteins is responsible for differences in the voltage range over which the channel opens. Thus, understanding how changes in voltage sensitivity are effected by changes in channel protein sequence illuminates the functional evolution of excitability. The K(V)1-family channel jShak1, from the jellyfish Polyorchis penicillatus, differs from most other K(V)1 channels in ways that are useful for studying the problem of how voltage sensitivity is related to channel sequence. We assessed the contributions of changes in sequence of the S4, voltage sensing, helix and changes in one asparagine residue in the S2 helix, to the relative stability of the open and closed states of the channel. Mutation of the neutral S2 residue (Asn227) to glutamate stabilized the open conformation of the channel. Different modifications of charge and length in S4 favoured either the closed conformation or the open conformation. The interactions between pairs of mutations revealed that some of the S4 mutations alter the conformation of the voltage-sensing domain such that the S4 helix is constrained to be closer to the S2 helix than in the wild-type conformation. These results, taken in conjunction with three-dimensional models of the channel, identify intra-molecular interactions that control the balance between open and closed states. These interactions are likely to be relevant to understanding the functional characteristics of members of this channel family from other organisms.

A new species of pontoniine shrimp belonging to the 'Periclimenes obscurus species group' is described from the Berau Islands, North East Kalimantan, Indonesia. Specimens were obtained from aglaopheniid hydrozoans of the genus Macrorhynchia. The new species is here described and figured. Its affinities with related species are discussed and a DNA-barcode is provided.

The bioluminescence emitted by Aequorea victoria jellyfish is greenish while its single bioluminescent photoprotein aequorin emits blue light. This phenomenon may be explained by a bioluminescence resonance energy transfer (BRET) from aequorin chromophore to green fluorescent protein (GFP) co-localized with it. However, a slight overlapping of the aequorin bioluminescence spectrum with the GFP absorption spectrum and the absence of marked interaction between these proteins in vitro pose a question on the mechanism providing the efficient BRET in A. victoria. Here we report the in vitro study of BRET between homologous Ca(2+)-activated photoproteins, aequorin or obelin (Obelia longissima), as bioluminescence energy donors, and GFP, as an acceptor. The fusions containing donor and acceptor proteins linked by a 19 aa peptide were purified after expressing their genes in Escherichia coli cells. It was shown that the GFP-aequorin fusion has a significantly greater BRET efficiency, compar...

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: ie 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 ...

We have identified a novel, multidomain, polymorphic lectin in the marine cnidarian Hydractinia echinata. The gene is expressed in oocytes and was therefore named CEL for cnidarian egg lectin. The predicted protein has an unusual domain architecture, consisting of variable numbers of thrombospondin type 1 domains, flanked by one N-terminal and two C-terminal galactose binding lectin domains. The diversity of the gene's transcripts results from allelic polymorphism as well as alternative splicing. Hydractinia is dioecious and its sex has been reported previously to be genetically determined. We found intersexual colonies that were functional males, but had immature CEL-positive oocytes alongside mature sperm in the same gonads. Intersexuality was observed to be common in one population but not found in others. Hermaphroditic, self-fertile colonies were found in one locality; however, in these cases gonads contained either male or female gametes without mixed ones. Intersexuality ...

In spite of considerable research effort on the “immortal jellyfish” Turritopsis dohrnii (Weissmann, 1883), a comprehensive account including the ontogenetic stages throughout its normal life cycle was still missing. Here we report the ontogeny of the medusa morph, with description of four consecutive stages distinguished by the morphology of the umbrellar apex and the number of marginal tentacles. Medusae reared at two different temperatures (14 °C and 25 °C) showed identical morphological features, but with shorter developmental time at higher temperature. Additional information on the morphology of the polyp stage is also provided. The implications for an easy morphological identification of T. dohrnii medusae from other congeneric species are discussed

The taxonomy of the putative superfamily Lafoeoidea (Hydrozoa), which includes the families Hebellidae and Lafoeidae, has been widely disputed at all systematic levels, mainly because these are morphologically simple and plastic animals. We used the molecular marker 16S mRNA to address phylogenetic relations of ‘Lafoeoidea’ hydroids mainly from shallow and deep waters of the north-east Atlantic and west Mediterranean. This study proves that the morphological simplicity of the ‘Lafoeoidea’ has led to several erroneous taxonomic assignments. We demonstrate that the superfamily ‘Lafoeoidea’ is not monophyletic and thus not valid; the families Hebellidae and Lafoeidae are polyphyletic. The ‘Lafoeidae’ subfamilies ‘Lafoeinae’ and ‘Zygophylacinae’ were recovered as monophyletic but quite distantly related and should be erected to the level of distinct families. The 16S haplotype data analysed in conjunction with morphological characters and distribution data were useful in differentiating morphologically undistinguishable, nominal and cryptic or pseudo-cryptic species, including undescribed taxa. Particularly within the ‘Lafoeinae’ group, unexpectedly high genetic biodiversity (including cryptic species) was encountered in the possibly not monophyletic genera Lafoea, Acryptolaria and Filellum. Cryptic diversity is also likely associated with the ‘Zygophylacinae’ nominal species Cryptolaria pectinata. The indications of genetic segregation by geographical distance of the ‘Lafoeoidea’ hydroids, particularly verified in deep waters, is probably a consequence of their reduced potential for large-scale dispersal, which likely interacts with the influence of the seabed topography, oceanographic circulation and adaptability to tolerate different abiotic conditions.