The switch from larval to adult globin gene expression in Xenopus laevis is mediated by erythroid cells from distinct compartments

The transition of hemoglobins during metamorphosis of Xenopus laevis involves replacement of the larval erythrocytes by adult ones, suggesting that the developmental control of this event depends upon the growth characteristics of the precursor cells. To identify the erythroid precursor cells and to investigate their developmental fate, we analyzed the distribution of stage-specific globin mRNAs by northern blotting in dorsal and ventral fragments of stage 32 embryos after in vitro culture as well as presumptive erythropoietic tissues of tadpoles during metamorphosis. The histological analysis shows that erythrocytes differentiate only in ventral fragments, suggesting that the ventral blood islands and most likely also the dorsolateral mesoderm are the primary sites of erythropoiesis. We also demonstrate that the first generations of erythrocytes, already express the predominating larval-specific alpha-globin mRNAs. The globin mRNA patterns obtained from presumptive erythropoietic tissues suggest an important role of circulating precursor cells in larval erythropoiesis, whereas the liver appears to be the main site of formation and maturation of the adult erythrocytes. Tentatively we propose that anuran erythropoiesis is dependent upon a self-perpetuating stem-cell line and that the larval and the adult erythrocytes are derived from successive generations of erythroid precursors, whose commitment may be imposed by the erythropoietic sites.     

Mutagenesis of the NH2-terminal domain of elongation factor Tu

Mutagenesis was carried out in the N-terminal domain of elongation factor Tu (EF-Tu) to characterize the structure-function relationships of this model GTP binding protein with respect to stability, the interaction with GTP and GDP, and the catalytic activity. The substitutions were introduced in elements around the guanine nucleotide binding site or in the loops defining this site, in the intact molecule or in the isolated N-terminal domain (G domain). The double substitution Val88----Asp and Leu121----Lys, two residues situated on two vicinal alpha-helices, influences the basic activities of the truncated factor to a limited extent, probably via long-range interactions, and induces a destabilisation of the G domain structure. The functional alterations brought about by substitutions on the consensus sequences 18-24 and 80-83 highlight the importance of these residues for the interaction with GTP/GDP and the GTPase activity. Mutations concerning residues interacting with the guanine base lead to proteins in large part insoluble and inactive. In one case, the mutated protein (EF-TuAsn135----Asp) inhibited the growth of the host cell. This demonstrates the crucial role of the base specificity for the active conformation of EF-Tu. The obtained results are discussed in the light of the three-dimensional structure of EF-Tu.     

Lowland river reference condition: spatial and temporal patterns of the zoobenthos community in the Volga headwaters (2006–2010)

The Volga, the largest river in Europe, has experienced multiple stressors from human activities. Recently we showed that its upper course (about 500 km, from its source to Tver) still has large sections with low impact and a natural type-specific potamal flora and fauna. Our present research in the East European lowlands aim to define reference conditions for mid-sized to large lowland rivers in order to build a basis for future management and conservation. Three monitoring sites were selected based on the results from intensive sampling in 2005. In subsequent field campaigns between 2006 and 2010 regular surveys were carried out each year in summer and additional ones in spring. A taxon-rich macroinvertebrate fauna, including several rare potamal relict species, was recorded and the data was used to provide an overview of annual and interannual variation in community indices and metrics. The conditions described for the headwaters of the Volga River system can be used as a reference state for medium-sized and large lowland rivers in regions where reference sites of these types are lacking.     

Die Datenbanken PaleoTax und Goniat - Vorstufen eines paläontologischen Informationssystems

The database systems PaleoTax and GONIAT provide detailed information on literature, taxonomy, morphology and occurrence of fossil invertebrate groups. PaleoTax is designed for Mesozoic corals, GONIAT for Paleozoic ammonoids, but both can be modified to cover other fossil groups. Both systems use dBASE format, but with different database structures. PaleoTax aims at the complete storage of all available objective data, GONIAT provides determinations based upon morphologic criteria, and includes information on geographic distribution and stratigraphic range of every taxon. A combination of both systems could lead to the establishment of a comprehensive paleontological information system useful for research and practical stratigraphic applications.     

Gonadal development and growth in 46,XX and 46,XY individuals with P450scc deficiency (congenital lipoid adrenal hyperplasia).

We have investigated gonadal development and growth in 4 individuals (3 with 46,XY and 1 with 46,XX karyotype) with P450scc deficiency. One patient died at 2 months of age from adrenal insufficiency, while the remaining 3 individuals were healthy and developed normally (age at follow-up: 18, 10 and 8 years). In the surviving individuals, the diagnosis was established during the first 2-4 months of life by extensive endocrine studies of blood and urine. In the remaining patient, the diagnosis was made on the basis of karyotype (46,XY), anatomy of internal and external genitalia and adrenal pathology. Gonadectomy was performed in the 2 surviving 46,XY individuals at the age of 7 years, and histological examination showed normal testicular morphology but very few germ cells. Postmortem examination of the testes of the 2-month-old subject showed normal testicular histology, and quantitative analysis revealed a normal number of germ cells. Ultrasound of the 46,XX individual showed normal internal female genitalia including ovaries with follicles. The 3 surviving patients grew along the 75th (46,XY), the 90th (46,XY) and the 50th percentile (46,XX), respectively. The oldest girl experienced normal breast and pubic hair development after oral estrogen replacement and topical testosterone administration. The glucocorticoid and mineralocorticoid replacement was adjusted in accordance with repeated measurements of serum sodium and serum potassium, plasma renin concentration and blood pressure. No attempts were made to normalize serum ACTH. We conclude that prenatal testicular maturation and development of female internal genitalia may take place in the absence of normal steroid hormone production. Normal growth and development may be obtained in P450scc-deficient individuals with adequate hormone replacement.     

Nitrogen Fixation in Continuous Culture with NH4Cl-Containing Media

N balance and ¹⁵N dilution were determined from growth of Azospirillum brasilense Sp7 and two unidentified gram-negative nitrogen-fixing microorganisms in continuous culture supplied with NH₄Cl. At the 1.1 and 2.2 mM NH₄Cl steady states (N-to-C ratios of 1:68 and 1:34, respectively), the organisms grew with NH₄Cl and N₂ as N sources simultaneously under carbon limitation. No ammonium could be detected in the supernatant of these cultures.     

Perspectives in marine science: A European point of view

Marine research has always been a field in science which was particularly open to, and at times dependent on, international cooperation, and this has become even more obvious during the last decade when issues of global change became central to any discussion. The global nature of scientific and other problems, required the development of new concepts and led to the establishment of new structures in research, coordination and funding on an international level. In Europe the 12 member European Community often served as a nucleus for larger networks and initiatives (e.g. COST, EUREKA), and in 1989 the EC itself launched a specific programme on marine research and technology (MAST). The various initiatives are not meant to replace, national efforts but to complement them — where added value arises from international cooperation, e.g. in global programmes like IGBP, WCRP and their various core projects. The focus of support for these programmes through international funding agencies and networks is not primarily on additional research money but more on structural support and coordination. In contrast, the MAST targeted projects on the North Atlantic margin and the Mediterranean also receive substantial basic support, and are designed to fill gaps left by other international research projects. Both EC and other projects profit from the coordinating measures offered by the EC Commission. A more efficient use of facilities (research vessels, special equipment) can be achieved by having central information services. Well-integrated international projects also require additional efforts in standardization of instrumentation, methods and units, with respect to sampling, sample processing and data treatment. Furthermore, the scope of the task to tackle questions of global change demands the development of new technologies like ROVs, biosensors, automatized sample and data acquisition and treatment, etc. Full exploitation of the results in scientific, political and economical terms is only facilitated through special concertation. Mathematical modelling of ecosystems is still in its infancy and needs further cooperative development in order to provide tools for forecasting and management. Finally, training and exchange of personnel on a European, and possibly wider, level needs to be intensified in order to meet the requirements of modern science.     

Rhizoferrin: A complexone type siderophore of the mocorales and entomophthorales (Zygomycetes)

The present investigation presents evidence that rhizoferrin, a novel polycarboxylate or complexone-type siderophore, originally isolated from Rhizopus microsporus, represents the common siderophore within the Zygomycetes. Thus, rhizoferrin could be detected by HPLC analysis in various families of the Mucorales, e.g., Rhizopus microsporus var. rhizopodiformis, Mucor mucedo and Phycomyces nitens (Mucoraceae), Chaetostylum fresenii and Cokeromyces recurvatus (Thamnidiaceae), Cunninghamella elegans and Mycotypha africana (Choanephoraceae) and Mortierella vinacea (Mortierellaceae) and in Basidiobolus microsporus (Entomophthorales). The function of rhizoferrin as a siderophore in the fungus R. microsporus var. rhizopodiformis was demonstrated by time- and concentration-dependent uptake of [55Fe]-labelled rhizoferrin, yielding saturation kinetics with values of Km = 8 microM and V(max) = 1.2 nmol min-1 (mg dry wt)-1.