Molecular and biological characterization of a mannan-binding lectin from the holothurian Apostichopus japonicus

To elucidate the origin and evolution of mannan-binding lectins (MBL), a new C-type lectin (CTL) specific for high-mannose glycans (MBL-AJ) was isolated from the coelomic plasma of the holothurian Apostichopus japonicus. MBL-AJ has oligomeric forms with identical 17-kDa subunits on SDS-PAGE. Among natural ligands, lectin hemagglutination activity was competitively inhibited by extracellular low-branched, but not high-branched, alpha-D-mannans isolated from marine halophilic bacteria and composed of alpha-1,2 and alpha-1,6 linked D-mannose residues. This suggests that the lectin interacts with backbone or inner side chain mannose residues, but not with terminal ones. The activity of the lectin was Ca(2+)-, pH-, and temperature-dependent. MBL-AJ cDNA was cloned from a holothurian coelomocyte cDNA library. The subunit of the mature protein has 159 amino acids and a single carbohydrate-recognition domain (CRD) of CTL. CRD contains a Glu-Pro-Asp amino acid sequence (EPN-motif) conserved for all known MBLs. A monospecific polyclonal antibody against MBL-AJ was obtained using the 34-kDa lectin dimer as an immunogen. The MBL-AJ has demonstrated immunochemical identity to the earlier isolated mannan-binding CTL from another holothurian, Cucumaria japonica. But a more interesting finding was cross-reactivity of MBL-AJ and human serum MBL detected by the antibody against MBL-AJ. Taking into consideration such MBL-AJ peculiarities as its carbohydrate specificity, the presence of a conserved region forming the mannose-binding site, common antigenic determinants with human MBL, and participation in defense reactions, it is possible that MBL-AJ belongs to the family of evolutionary conserved mannan-binding proteins.     

MAJOR GENETIC DIFFERENCES BETWEEN CROWN-OF-THORNS STARFISH (ACANTHASTER PLANCI) POPULATIONS IN THE INDIAN AND PACIFIC OCEANS

Spatial variation in allelic frequencies at nine allozyme loci were assayed in 20 populations of the crown-of-thorns starfish, Acanthaster planci, collected throughout the Pacific and Indian Oceans. These data were analyzed together with published data, for the same loci, from an additional 19 populations, giving a total sample size of approximately 1800 individuals. There was a marked discontinuity between the Indian and Pacific Ocean populations, but those off Western Australia and from the Southeast Asian region had a strong Pacific affinity. The genetic groups were congruent with the distributions of two color morph groups: gray-green to red-brown forms in the Pacific and a blue to pale red form in the Indian Ocean. These patterns of genetic structure are similar to those described for the starfish Linckia laevigata, which has similar life-history characteristics. Vicariant events may have influenced some populations within the Pacific, but the allozyme data cannot resolve the effects of these events clearly. Patterns of variation within regions were consistent with isolation by distance, but, at larger scales, were obscured by regional vicariance and some outliers, particularly by apparently high levels of gene flow between Japan and the Great Barrier Reef, Australia. Apparent gene flow between population pairs was not closely related to present-day ocean currents. The results demonstrate a strong influence of allopatric separation on genetic divergence at large geographic scales, but also show evidence of slow rates of change in gene frequencies consistent with the large population sizes of this species. Low levels of divergence between groups demonstrate the genetic structure is recent (Pleistocene) and are likely responses to changes in climate and sea level.     

Expression of two different sulfated fucans by females of Lytechinus variegatus may regulate the seasonal variation in the fertilization of the sea urchin

The egg jellies of sea urchins contain sulfated polysaccharides with unusual structures, composed of linear chains of l-fucose or l-galactose with well-defined repetitive units. The specific pattern of sulfation and the position of the glycosidic bond vary among sulfated polysaccharides from different species. These polysaccharides show species specificity in inducing the acrosome reaction, which is a critical event for fertilization. Females of the sea urchin Lytechinus variegatus spawn eggs containing a sulfated fucan with the repetitive sequence [3-alpha-L-Fucp-2(OSO(3))-1 --> 3-alpha-L-Fucp-4(OSO(3))-1 --> 3-alpha-L-Fucp-2,4(OSO(3))-1 --> 3-alpha-L-Fucp-2(OSO(3))-1](n). We now observe that, close to winter, a period of decreased fertility for the sea urchin, the females synthesize a distinct sulfated fucan with a simple structure, composed of 4-sulfated, 3-linked alpha-fucose residues. This sulfated fucan is inactive when tested in vitro for the acrosome reaction using homologous sperm. The amount of egg jellies spawned by females (and their constituent sulfated polysaccharides) varied greatly throughout the year. Apparently, there is a correlation between the temperature of the sea water and the expression of the 4-sulfated, 3-linked sulfated fucan. Overall, we described the occurrence of two isotypes of sulfated fucan in the egg jelly of the sea urchin L. variegatus, which differ in their biological activity and may be involved in the periodicity of the reproductive cycle of the invertebrate.     

A comparative analysis of egg provisioning using mass spectrometry during rapid life history evolution in sea urchins

A dramatic life history switch that has evolved numerous times in marine invertebrates is the transition from planktotrophic (feeding) to lecithotrophic (nonfeeding) larval development—an evolutionary tradeoff with many important developmental and ecological consequences. To attain a more comprehensive understanding of the molecular basis for this switch, we performed untargeted lipidomic and proteomic liquid chromatography‐tandem mass spectrometry on eggs and larvae from three sea urchin species: the lecithotroph Heliocidaris erythrogramma, the closely related planktotroph Heliocidaris tuberculata, and the distantly related planktotroph Lytechinus variegatus. We identify numerous molecular‐level changes possibly associated with the evolution of lecithotrophy in H. erythrogramma. We find the massive lipid stores of H. erythrogramma eggs are largely composed of low‐density, diacylglycerol ether lipids that, contrary to expectations, appear to support postmetamorphic development and survivorship. Rapid premetamorphic development in this species may instead be powered by upregulated carbohydrate metabolism or triacylglycerol metabolism. We also find proteins involved in oxidative stress regulation are upregulated in H. erythrogramma eggs, and apoB‐like lipid transfer proteins may be important for echinoid oogenic nutrient provisioning. These results demonstrate how mass spectrometry can enrich our understanding of life history evolution and organismal diversity by identifying specific molecules associated with distinct life history strategies and prompt new hypotheses about how and why these adaptations evolve.     

Radial Glia in Echinoderms

Radial glial cells are crucial in vertebrate neural development and regeneration. It has been recently proposed that this neurogenic cell type might be older than the chordate lineage itself and might have been present in the last common deuterostome ancestor. Here, we summarize the results of recent studies on radial glia in echinoderms, a highly regenerative phylum of marine invertebrates with shared ancestry to chordates. We discuss the involvement of these cells in both homeostatic neurogenesis and post‐traumatic neural regeneration, compare the features of radial glia in echinoderms and chordates to each other, and review the molecular mechanisms that control differentiation and plasticity of the echinoderm radial glia. Overall, studies on echinoderm radial glia provide a unique opportunity to understand the fundamental biology of this cell type from evolutionary and comparative perspectives.     

Pelmatozoan arms from the Middle Cambrian of Australia: bridging the gap between brachioles and brachials?

The early Middle Cambrian Monastery Creek Phosphorite (Beetle Creek Formation, Queensland, Australia) contains an assemblage of disarticulated echinoderm ossicles that are exquisitely preserved. Amongst this material we recognize pelmatozoan brachials, radials, basals and holomeric columnals. Although we cannot reconstruct the complete animal with precision, these elements represent the oldest known pelmatozoan with crinoid-like appendages. Key elements include isotomously to heterotomously branched uniserial appendage plates with a tripartite adoral food groove, a longitudinal central canal interpreted as housing entoneural nerve, and differentiated articulation facets. There are also epispire-bearing radials bearing one to four arm insertion-facets, each one pierced by a central neural canal. These canals run internal towards the oral area beneath the external food groove. Co-occuring material includes single truncated cone-shaped basals and holomeric columnals, both with a similar articulation pattern, and irregular, epispire-bearing thecal plates. This mosaic of crinozoan (uniserial isotomous to heterotomous arms with neural canal), blastozoan (epispire-bearing thecal plates, appendage leading to oral thecal food groove without direct connection with body cavity) and apomorphic characters (circumoral instead of basal entoneural plexus) is unexpected and demonstrates that crinoid-like pelmatozoans with uniserial, branched arms appeared significantly earlier than the Tremadocian, when the first articulated crinoid skeletons are found. It also raises questions about the polyphyletic appearance of feeding appendages among pelmatozoan echinoderms.     

Larval transfer and the origins of larvae

Larval transfer is presented as an alternative to the widely held assumption that larvae and corresponding adults have always evolved together, within the same lineage. I submit (1) that genes specifying the basic forms of all embryos and larvae originated as the genomes of animals that matured without metamorphosis, (2) that such genomes have been transferred by hybridization, and (3) that fertile hybrids have been produced at infrequent and irregular intervals between animals at all levels of relationship during the course of evolution. The origins of blastulas, hydromedusae, protostome and deuterostome ciliated larvae, arthropodan larvae and urochordate tadpoles are discussed as examples of my hypothesis. I believe that practically all metazoans have at least one inter-group hybrid in their ancestry. Larval transfer is briefly considered in relation to other theories on ontogeny and phylogeny. Methods of verification are suggested.     

Fasciole pathways in spatangoid echinoids: a new source of phylogenetically informative characters

Fascioles are important early-forming structures that play a key role in allowing irregular echinoids to burrow. They have traditionally been grouped into a small number of types according to their general position on the test, but this masks some significant differences that exist. The precise course that fasciole bands follow over the test plating has been mapped in detail for 89 species of spatangoid echinoids, representing the great majority of fasciole-bearing genera both living and fossil. Within each fasciole type, discrete and conserved patterns can be distinguished, differing both in which plates they are initiated on, and on whether they cross plate growth centres or are late-stage bands positioned towards the edge of the plate. Fasciole position is most highly conserved in the anterior and lateral interambulacral plates and on the earliest forming bands. The existence of different subanal fasciole patterns in the Micrasteridae and Brissidae suggests that these may have evolved independently. Schizasterid and hemiasterine spatangoids can each be subdivided into two major clades, and brissid spatangoids into three clades based on detailed patterns of their fascioles. Plotting fasciole pathways over test architecture provides a rich new source of phylogenetically informative characters.  © 2005 The Linnean Society of London, Zoological Journal of the Linnean Society , 2005, 144 , 15−35.     

Coelomocyte Morphology in the Holothurians Apostichopus japonicus (Aspidochirota: Stichopodidae) and Cucumaria japonica (Dendrochirota: Cucumariidae)

The cellular composition of the coelomic fluid of the Far Eastern holothurinans Apostichopus japonicus and Cucumaria japonica was studied using light and transmission electron microscopy and histochemistry. In the coelomic fluid of A. japonicus, the following types of coelomocytes were distinguished: progenitor cells; amoebocytes; vacuolated cells; small (or young) morula cells; morula cells of type I, type II, and type III; crystal cells; and vibratile cells. In the coelomic fluid of C. japonicawere found progenitor cells, amoebocytes, vacuolated cells, morula cells of type I and type II, crystal cells, and hemocytes containing a respiratory pigment. The issue of stem cell type, which gives rise to coelomocytes, is discussed.     

An Evolutionary Scenario For The Origin Of Pentaradial Echinoderms—Implications From The Hydraulic Principles Of Form Determination

The early evolutionary history of echinoderms was reconstructed on the basis of structural-functional considerations and application of the quasi-engineering approach of ‘Konstruktions-Morphologie’. According to the presented evolutionary scenario, a bilaterally symmetrical ancestor, such as an enteropneust-like organism, became gradually modified into a pentaradial echinoderm by passing through an intermediate pterobranch-like stage. The arms of a pentaradial echinoderm are identified as hydraulic outgrowths from the central coelomic cavity of the bilateral ancestor which developed due to a shortening of the body in length but widening in the diameter. The resulting pentaradial symmetry is a consequence of mechanical laws that dictate minimal contact surface areas among hydraulic pneumatic entities. These developed in the coelomic cavity (metacoel) in the bilaterally symmetrical ancestor, when from the already U-shaped mesentery with the intestinal tract two additional U-shaped bows developed directly or subsequently. During the subsequent development tensile chords of the mesentery ‘sewed’ the gut with the body wall first in three and secondly in five ‘seams’. During the direct development five ‘seams’ between tensile chords and body wall developed straightly. These internal tensile chords subdivide the body coelom into five hydraulic subsystems (‘pneus’), which eventually arrange in a pentaradial pattern. The body could then enlarge only between the tensile chords, which means that five hydraulic bulges developed. These bulges initially supported the tentacles and finally each of them enclosed the tentacle until only the feather-like appendages of the tentacles projected over the surface. The tentacles with their feathers were transformedinto the ambulacral system, and the bulges become the arms. These morphological transformations were accompanied and partly determined by specific histological modifications, such as the development of mutable connective tissues and skeletal elements that fused to ossicles and provided shape stabilization in form of a calcareous skeleton in the body wall. The organism resulted was an ancestral echinoderm (‘Ur-Echinoderm’) with an enlarged metacoel, stabilized by hydraulic pressure working againsta capsule of mutable connective tissue, skeletal elements and longitudinal muscles. In regard to these reconstructions, the body structure of echinoderms can be understood as a hydraulic skeletal capsule.