Characterization and developmental regulation of a gene expressed specifically in the skeletogenic lineage of the sea urchin embryo

The sea urchin embryonic skeleton, or spicule, is deposited by mesenchymal progeny of four precursor cells, the micromeres, which are determined to the skeletogenic pathway by a process known as cytoplasmic localization. A gene encoding one of the major products of the skeletogenic mesenchyme, a prominent 50 kD protein of the spicule matrix, has been characterized in detail. cDNA clones were first isolated by antibody screening of a phage expression library, followed by isolation of homologous genomic clones. The gene, known as SM50, is single copy in the sea urchin genome, is divided into two exons of 213 and 1682 bp, and is expressed only in skeletogenic cells. Transcripts are first detectable at the 120 cell stage, shortly after the segregation of the skeletogenic precursors from the rest of the embryo. The SM50 open reading frame begins within the first exon, is 450 amino acids in length, and contains a loosely repeated 13 amino acid motif rich in acidic residues which accounts for 45% of the protein and which is possibly involved in interaction with the mineral phase of the spicule.

The important cis-acting regions of the SM50 gene necessary for proper regulation of expression were identified by gene transfer experiments. A 562 bp promoter fragment, containing 438 bp of 5' promoter sequence and 124 bp of the SM50 first exon (including the SM50 initiation codon), was both necessary and sufficient to direct high levels of expression of the bacterial chloramphenicol acetyltransferase (CAT) reporter gene specifically in the skeletogenic cells. Removal of promoter sequences between positions -2200 and -438, and of transcribed regions downstream of +124 (including the SM50 intron), had no effect on the spatial or transcriptional activity of the transgenes.

Regulatory proteins that interact with the SM50 promoter were identified by the gel retardation assay, using bulk embryo mesenchyme blastula stage nuclear proteins. Five protein binding sites were identified and mapped to various degrees of resolution. Two sites are homologous, may be enhancer elements, and at least one is required for expression. Two additional sites are also present in the promoter of the aboral ectoderm specific cytoskeletal actin gene CyIIIa; one of these is a CCAA T element, the other a putative repressor element. The fifth site overlaps the binding site of the putative repressor and may function as a positive regulator by interfering with binding of the repressor. All of the proteins are detectable in nuclear extracts prepared from 64 cell stage embryos, a stage just before expression of SM50 is initiated, as well as from blastula and gastrula stage; the putative enhancer binding protein may be maternal as well.

Time for a Sea Change: a Study of the Effectiveness of Biodiversity Conservation Measures and Marine Protected Areas Along Southern Thailand’s Andaman Sea Coastline

This study examines how Thailand’s biodiversity conservation measures affect fishing communities, especially in the marine protected areas (MPAs) on the Andaman Sea coastline. It documents the various efforts of the local fishing communities to protect the resources in the area. Also included are recommendations for government agencies, civil society and the international community. [PDF contains 94 pages]

Chrysosphaerella and the phytoplankton of the Little Sea, Dorset

The Little Sea is an 80-acre, shallow freshwater lake formed about a hundred years ago by sand-dunes cutting off a sea-inlet at Studland Bay, near Swanage. This work presents a general survey of the phytoplankton in the lake from October 1990 to December 1993. Many species were present throughout the year; others showed seasonal variations. Numerically, the diatoms, Monoraphidium and sometimes Rhodomonas, were the main constituents of the phytoplankton. One species of alga in the lake of particular interest is Chrysosphaerella longispina Lauterb. which, up to 1991, had only been recorded from five localities in Britain.

Plant nutrients and major ions in the Little Sea, Studland, Dorset

This short paper records some measurements made on the Little Sea, a shallow, coastal, acidic lake on Studland Heath, Dorset. The lake, formed about 100 years ago by dunes cutting off a sea inlet, has not received any input of agricultural fertilizers or other waste products for at least the last 30 years. It is a Site of Special Scientific Interest (SSSI). Samples of surface water were taken from the northern and southern ends of the lake at 3-monthly intervals, from July 1995 to April 1996. The first samples in July 1995 were taken during a period of drought; rain, sometimes very heavy, came in late September. With the exception of silicate, potassium and phosphate, there were no large changes in plant nutrient concentrations during the year. The concentration of nitrate-nitrogen was very low (close to the limits of analytical detection), but total phosphorus at ca. 30 mu g per litre was similar to concentrations found in some of the Cumbrian eutrophic lakes. The large number of algal species at low cell/colony concentrations suggested that the lake is mesotrophic. Sodium, chloride and magnesium in the lake water were close to the same proportions as those found in sea water. Dry and wet deposition of sea-salts on the lake surface and its catchment area probably is the major source of sodium, magnesium and chloride ions in the lake, and also accounts for about half of the mean potassium and sulphate concentrations.

A simple approach for the estimation of food consumption from growth rates at different environmental conditions and its application to juvenile cod (Gadus morhua L.) of a fjordic sea loch on the west coast of Scotland

Abstract Growth and condition of fish are functions of available food and environmental conditions. This led to the idea of using fish as a “consumption sensor” for the measurement of food intake over a defined period of time. A bio-physical model for the estimation of food consumption was developed based on the von Bertalanffy model. Whereas some of the input variables of the model, the initial and final lengths and masses of a fish and the temperature within the time period considered can easily be measured, internal characteristics of the species have to be determined indirectly. Three internal parameters are used in the model: the maintenance consumption at 0°C, the temperature dependence of this consumption and the food efficiency, the percentage of the ingested food utilized. Estimates of the parameters for a given species can be determined by feeding experiments. Here, data from published feeding experiments on juvenile cod, Gadus morhua L., were used to validate the model. The average of the relative error for the food intake predicted by the model for individual fish was about 24 %, indicating that fish used the food with different efficiencies. However, grouping the fish according to size classes and temperature lowered the relative error of the predicted food intake for the group to typically 5 %. For a group containing all fish of the feeding experiment the relative prediction error was about 2 %. Zusammenfassung Wachstum und Kondition der Fische sind von der verfügbaren Nahrung und von Umweltbedingungen abhängig. Dies führte zur Idee, Fisch als „Konsum-Sensor“ für die Messung der Nahrungsaufnahme über einen definierten Zeitraum zu verwenden. Auf Grundlage des von Bertalanffy-Modells wurde ein bio-physikalisches Modell zur Schätzung der Futteraufnahme entwickelt. Während einige der Eingangsgrößen des Modells leicht gemessen werden können (Anfangs- und Endlänge und -körpermasse der Fische und die Temperatur innerhalb des betrachteten Zeitraum), können interne Parameter der betrachteten Art nur indirekt bestimmt werden. Drei interne Parameter werden in dem Modell verwendet: Die Erhaltungskonsumtion bei 0° C, die Temperaturabhängigkeit dieser Rate und der Wirkungsgrad der Nahrung (der Anteil der Nahrung ,der aufgenommen und verwendet und nicht ungenutzt wieder ausgeschieden wird). Die Modellparameter für eine bestimmte Art können durch Fütterungsversuche bestimmt werden. Um das Modell zu validieren wurden Daten aus veröffentlichten Fütterungsversuchen mit juvenilen Kabeljau (Gadus morhua L.) verwendet. Modell und Wirklichkeit weichen in der Regel voneinander ab. Der durchschnittliche relative Fehler der durch das Modell vorhergesagten Nahrungsaufnahme betrug für Einzelfische etwa 24%, was darauf hinweist, dass einzelne Fisch die Nahrung mit unterschiedlichen Wirkungsgraden verwerten. Allerdings senkte die Gruppierung der Fische nach Größenklassen und Temperatur den relativen Vorhersagefehler für die Nahrungsaufnahme der Gruppe auf etwa 5%. Für alle Fische im Fütterungsversuch ist der relative Vorhersagefehler etwa 2%.

Value chain analysis for sea cucumber in the Philippines

This study examined the sea cucumber industry in the Philippines through the value chain lens. The intent was to identify effective pathways for the successful introduction of sandfish culture as livelihood support for coastal communities. Value chain analysis is a high-resolution analytical tool that enables industry examination at a detailed level. Previous industry assessments have provided a general picture of the sea cucumber industry in the country. The present study builds on the earlier work and supplies additional details for a better understanding of the industry's status and problems, especially their implications for the Australian Center for International Agricultural Research (ACIAR) funded sandfish project "Culture of sandfish (Holothuria scabra) in Asia- Pacific" (FIS/2003/059). (PDF contains 54 pages)

A study of the durability of concrete in sea water

The durability of concrete in sea water has been a very widely debated question from the time that disintegration of concrete in sea water first became evident. Numerous investigations and reports have been made of isolated structures in various parts of the country and from these, hasty conclusions have been reached which engineers, situated where different conditions prevail, have not been warranted in accepting. A few engineers have made investigations of a much wider scope and consequently their conclusions should be given greater weight.

Mellum Island (southern North Sea): dynamic processes and sedimentary structures. I. Southern tidal flat, transition zone and high-surface.[p.72 (Blasensand) only][Translation from: Senckenbergiana Maritima 11, 59-113, 1979]

This partial translation of a longer article describes the phenomenon of ”Blasensand”. Blasensand is formed when sedimentation of dried out sand is suddenly flooded from above. A more detailed explanation of Blasensand is given in this translated part of the paper.

Mitochondria and the development of sea urchin embryos

After artificial activation or fertilization of non-nucleate fragments or eggs of the sea urchin, the mitochondria actively synthesize RNA. The RNA made in non-nucleate fragments is shown to be mostly single stranded and to be associated primarily with the low speed pellet of centrifuged cellular homogenates.

Protein synthesis is observed in non-nucleate fragments in the presence or absence of the mitochondrial RNA synthesis: it is found to be qualitatively similar but quantitatively less in the absence of the RNA synthesis. The continued syntheses of proteins in the non-nucleate fragments in the absence of mitochondrial RNA synthesis provides additional evidence for the presence of a stable messenger RNA component in the unfertilized sea urchin egg.

Since the uptake or actinomycin D was found to be inhibited by the presence of a fertilization membrane, ethidium bromide, at 10 μgs/ml, is used as an effective inhibitor of RNA synthesis in non-nucleate fragments and in early cleavage stage embryos. However, this same concentration of ethidium bromide is found to be only partially effective in blocking RNA synthesis at the mesenchyme blastula stage of development.

Low concentrations of ethidium bromide (2 and 5 μgs/ml) are found not to be lethal but to be capable of producing moderate developmental defects. In the presence of concentrations of ethidium bromide adequate to inhibit all the mitochondrial RNA synthesis (10 μgs/ml of ethidium bromide), from fertilization on, the embryos do not cleave beyond the 4-8 cell stages. When similar concentrations of ethidium bromide are added at an early mesenchyme blastula stage, the embryos do not gastrulate but continue to swim for more than 24 additional hours (adequate for control embryos to develop to a late prism stage). These results lead to the conclusion that mitochondrial RNA synthesis may be very essential for normal development to occur.

DNA is synthesized in the non-nucleate fragments of sea urchin eggs. None of the newly synthesized DNA is found in the closed circular form. When phenol extracted directly from the fragments, the DNA is found to sediment at approximately 38 and 27s in sucrose gradients but neither of these size classes could be found associated with the isolated mitochondria. The template for the synthesis of DNA in non-nucleate fragments remains unknown.

Concerning the current conditions and transport of sand in the shallow water areas off the coast of the south-eastern North Sea [Translation from: Hamburger Kustenforschung 29 [pages 41-43 only], 1974]

With the aid of the German Research Association in the central programme 'Sand movements in the German coastal region', an investigation into the current conditions in the shallow water areas of the coasts of the south-eastern North Sea between Sylt and the Weser estuary was carried out by the author. Foundations of the work are 19 continuous current recordings in five profiles normal to the coast from years 1971 to 1973. Off the coasts of the south-eastern North Sea varying tidal currents impinge; they are currents whose directions may vary periodically through all points of the compass. They are caused by the circulating tides in the North Sea (Amphidromien). The turning flow movement experiences a deformation in the very shallow coastal waters, and as it happens the flow turning movement in the case of high tide continues right up onto the outer flats, while here and in the fore-lying shallow water areas around the time of low water (on account of the small depths of waters), there prevails a more variable current. A result of this hydrodynamical procedure is the development of counter currents. This partial translation of the original paper provides the summary of this study of of the mudflat areas between the Elbe and Weser.