Autecological investigations on marine diatoms. 5:Coscinodiscus concinnus W. Smith andRhizosolenia setigera Brightwell

The cold oligo-eurytherm diatomsCoscinodiscus concinnus W. Smith andRhizosolenia setigera Brightwell were cultured to determine their best competitive position by growth. Comparison of their generation times with those of other diatoms indicate that they reach this position between 6°C and 12°C. Both species grew between –1.5°C and about 20°C. The experiments indicate thatC. concinnus flowerings are possible in a deep water column, during periods of high light intensities. The simultaneous death of species in the upper layer is also caused by high light intensities.C. concinnus appeared in two morphological forms; the normal voluminous form, and a flatter form with a few intercalary bands only, filled with large oil-droplets. The latter appeared at 0°C and below, and at the upper temperature limit for growth of about 19°C–20°C. The separation of nov. spec. fromC. concinnus based on the absence or presence of a hyaline area and intercalary bands as identification characteristics should be reconsidered.     

Analysis of a second family with hereditary non-chromaffin paragangliomas locates the underlying gene at the proximal region of chromosome 11q

The gene for autosomal, dominantly inherited, non-chromaffin paragangliomas has previously been mapped at 11q23-qter by linkage analysis of a single family. In the present study, we have used genetic markers from 11q for the analysis of two distantly related pedigrees with the same disorder. Linkage analysis and haplotyping indicate that the gene underlying the disorder in the present family is located on chromosome 11q proximal to the tyrosinase gene locus (11q14–q21). Closely linked markers are the human homologue of the murine INT2 protooncogene and the anonymous DNA marker D11S527. A maximum lod score of 5.4 (=0.0) has been obtained for linkage between the disorder and the chromosomal region defined by these markers. The human INT2 gene can be regarded as a candidate for the disorder on the basis of its expression pattern during embryogenesis in the mouse. However, haplotype analysis indicates that this gene is probably not the predisposing genetic factor in the present family.     

The pelagic system in the photic zone of the tropical Atlantic

Summary A multidisciplinary study of the carbon budget in the upper 300 meter of permanently stratified waters was started by two NECTAR-expeditions (North Equatorial Current Trans Atlantic Research) with HMS TYDEMAN in 1977 and 1978 (BAARS, ZIJLSTRA and TIJSSEN, 1979). In 1979 additional measurements were performed during the Gulf of Guinea-expedition with MS TYRO.Primary production in the nutrient depleted mixed layer of the North Equatorial Current estimated from the diurnal cycle in the O₂ concentration (TIJSSEN, 1979) and in POC (POSTMA and ROMMETS, 1979) revealed values 4–10 times higher than the data from the¹⁴C method in the literature: 800–2000 against ca. 200 mg C/m²/day. Moreover,¹⁴C incubations performed in bottle volumes of 4 liter and over 2 hour periods, instead of the recommended 12 hours for oligotrophic waters, gave 5–15 times higher values as incubations in the commonly used 300 ml (or smaller) bottles (GIESKES, KRAAY and BAARS, 1979). In the latter bottles a dramatic decrease of chlorophyll concentrations was observed, suggesting either heavy damage to fragile microflagellates by glasswall contacts and/or insufficient nutrient recycling by the lack of zooplankton in small samples. This then could account for the phenomena of low production and decreasing algal stock in long incubations with small bottles. These results suggest that today's picture of the primary production in the world's oceans (DE VOOIJS, 1979) needs probably a thorough reexamination. On the other hand, experiments in the North Sea and in the Gulf of Guinea did not indicate an effect of bottle size on¹⁴C incorporation and the¹⁴C method gave comparable estimates of primary production as the high precision oxygen method (photometric endpoint detection in the Winkler titration,cf. TIJSSEN, 1979). However, in these waters nutrient concentrations are always clearly above detection levels so that all previous data from somewhat richer areas may have been correct. In relation to the large oligotrophic parts of the oceans a question remains about the fate of the probably high primary production. Is it consumed by the algae themselves by night (POSTMA, 1980), are bacteria and microzooplankton more important consumers than formerly thought, or is the daily ration of zooplankters much higher as expected from extrapolation of filtration experiments in more eutrophic waters? We hope to clarify this topic during the coming NECTAR'82 expedition.Another main objective of the programme concerns the character of the deep chlorophyll maximum in permanently stratified waters. This layer is in the North Equatorial Current located at the depth of the nitratocline and at ca. 1% of the incident light at the surface (SPITZER and WERNAND, 1981). Primary production in the layer seems to be negligible while detailed vertical profiles of zooplankton, obtained with a Longhurst-Hardy Plankton Recorder, revealed no obvious concentrations in the layer. Chlorophyll analysis by thin-layer-chromatography (GIESKES, KRAAY and TIJSSEN, 1978) demonstrated that more than half of the chlorophyll a in the layer consists of an isomer which bleaches rapidly when transferred to higher light levels. The hypothesis was formulated that the chlorophyll maximum layer, at least in this region of the Atlantic, is an accumulation of chlorophyll breakdown products with a quite long turnover time at low light levels. In contrast to these findings, chlorophyll maxima near West-Africa and in the Gulf of Guinea were located at 5–10% light and contained more living algal cells (most of them as small as 1–3 m) than the nutrientpoor mixed layer above it. Primary production profiles had therefore a bimodal shape, with peaks at 30–50% light and at the chlorophyll maximum. Chlorophyll isomers, now analysed with High Pressure Liquid Chromatography, were also in these waters present at nearly all stations and comprised 30–70% of total chlorophyll comparable to the situation in the North Equatorial Current (GIESKES and KRAAY, 1981). It could be shown that these isomers are not involved in primary production, so that well established relationships between chlorophyll, light and primary production, found in oceanographic literature, have to be reconsidered.     

Autecological investigations on marine diatoms. I. Experimental results in biogeographical studies

Summary The upper and/or lower temperature limits for growth of 43 marine diatoms have been determined. According to the extent of the temperature tolerance range for growth and its position within the ecological relevant temperature range, the diatoms were divided in oligo-eurytherm (cold-, temperate-, warm-), meso-eurytherm (cold-, warm-) and eu-eurytherm species.The definition of the terms cosmopolites and circum-tropical could be enlarged, when the experimentai results and the distribution data from literature (19 distribution maps were combined.The results showed a significant relation between lower temperature limit for growth and both volume and cell size. In this way the lower temperature limit influences the size distribution of the phytoplankton in the oceans. Large diatoms are absent in cold water because of their high lower temperature limit for growth.The use of experimental results to reduce the number of sampling stations for determination of geographical distribution of diatoms, is discussed.     

Antigenic relationship of influenza-virus neuraminidases from Asian,Hong Kong,and Equi-2 strains

Two Asian influenza strains, the Hong Kong strain and an Equi-2 influenza strain have been investigated. Adsorption isotherms of purified neuraminidases from these strains with isolated antibodies from homologous antisera are given. Cross testing by neuraminidase inhibition and haemagglutination inhibition are reported. Hong Kong neuraminidase appears to be indistinguishable from the earlier Asian neuraminidases, and not related to Equi-2 influenza neuraminidase. The haemagglutinin from the Hong Kong strain is related to earlier Asian strains as well as to the equine strain.In collaboration with the Chief Medical Officer of Health and Epidemiology, Department of Public Health, Den Haag, The Netherlands.It is a pleasure to express our thanks to Mr. J. Jacobs, N. V. Philips Duphar, Weesp (The Netherlands) for his interesting discussions and suggestions; and to Mr. H. de Jonge, Department of Medical Statistics, University of Leiden (The Netherlands) for his advice.     

Not just any ICD device in patients with long-QT syndrome

Patients with LQT syndrome are prone to lifethreatening arrhythmias. After surviving such an event, implantation of an ICD is indicated. There are, however, special subtle demands in the treatment of these patients. In this case report we describe our findings in a patient with LQT1 syndrome, and the pitfalls that can and must be avoided. (Neth Heart J 2007;15:418-21.)     

Mutual control of membrane fission and fusion proteins

Membrane fusion and fission are antagonistic reactions controlled by different proteins. Dynamins promote membrane fission by GTP-driven changes of conformation and polymerization state, while SNAREs fuse membranes by forming complexes between t- and v-SNAREs from apposed vesicles. Here, we describe a role of the dynamin-like GTPase Vps1p in fusion of yeast vacuoles. Vps1p forms polymers that couple several t-SNAREs together. At the onset of fusion, the SNARE-activating ATPase Sec18p/NSF and the t-SNARE depolymerize Vps1p and release it from the membrane. This activity is independent of the SNARE coactivator Sec17p/alpha-SNAP and of the v-SNARE. Vps1p release liberates the t-SNAREs for initiating fusion and at the same time disrupts fission activity. We propose that reciprocal control between fusion and fission components exists, which may prevent futile cycles of fission and fusion.     

Assembly and overexpression of membrane proteins in Escherichia coli

The bacterium Escherichia coli is one of the most popular model systems to study the assembly of membrane proteins of the so-called helix-bundle class. Here, based on this system, we review and discuss what is currently known about the assembly of these membrane proteins. In addition, we will briefly review and discuss how E. coli has been used as a vehicle for the overexpression of membrane proteins.     

Is it possible to replace stimulus animals by scent-filled cups in the social discrimination test?

A study in which the rat social discrimination test was refined is described. This test measures social memory by using, in general, juvenile rats as stimulus animals. Rats are offered a first juvenile to investigate (learning trial), and after a specified interval, the rats are offered the same rat and a second juvenile rat to investigate again (retrieval trial). When the rats sniff the second juvenile in the retrieval trial more than the first, social memory for the second juvenile is said to be present. This test is mainly based on scents from the juvenile. Attempts were made to refine the test to reduce the number of animals used, to enhance the scope of the test, and to improve its validity. Firstly, the stimulus animals were replaced by the scent of juveniles, in the form of cups filled with sawdust taken from cages of juvenile rats. Similar results to those in the original test were obtained when using these scents. Furthermore, male and female scents were tested, and showed the same results as for the juvenile scents. Secondly, rats were also given two cups (one scent-filled and one filled with plain sawdust) in the learning trial, to determine which allowed a more-precise delineation of motivational, discriminatory and memory components. Overall, it is possible to replace stimulus animals by scent-filled cups in the social discrimination test, to enhance the scope of the test, and to draw more-valid conclusions with respect to social memory.