Inhibitory effects of orotate on precursor incorporation into nucleic acids.

The influence of orotic acid on the incorporation of precursors into nucleic acids was studied in mice and rats and in isolated cells. In vivo, orotate levels were modified by two diets which are known to increase the rate of pyrimidine nucleotide synthesis in rat liver. Of these diets, a 1% orotate diet had greater inhibitory effects than an arginine-deficient diet on the incorporation of [3H]orotate into RNA of mouse kidney than mouse liver. This contrasted with the situation in the rat where there was a greater effect in the liver than the kidney. The situation in the rat was more readily interpreted than in the mouse in terms of previously established effects of these diets on ribonucleotide pool sizes. However, studies using [3H]adenosine as a precursor for incorporation into RNA suggested that even in the mouse the effects of orotate were on pool sizes rather than an inhibitory effect on RNA synthesis. The incorporation of [3H]thymidine into DNA was inhibited by orotate to a similar degree in cultured HTC hepatoma cells and a line of rat liver epithelial cells. An effect on DNA synthesis rather than solely on pool sizes was suggested by the observation that the pool size of dTTP was not increased by 5 mM orotate under conditions in which there was a four-fold increase in the level of UTP in HTC cells. An inhibitory effect of orotate on DNA synthesis was further supported by an observation of decreased incorporation of [3H]deoxyadenosine into DNA and a lower rate of cellular proliferation.     

Plasmodium falciparum: isolation and purification of spontaneously released merozoites by nylon membrane sieves

A new procedure for isolating spontaneously released merozoites from in vitro cultures of Plasmodium falciparum (FVO and FCB strains) is described. The mature forms of relatively synchronous cultures containing predominantly trophozoites and few schizonts were concentrated with Plasmagel and then incubated at 37 C, without adding fresh red blood cells, until trophozoites matured into schizonts. Merozoites which were subsequently released were harvested and freed from host red blood cell material by low-speed centrifugations and nylon membrane sieves (3- and 1.2-μm pore size). From a culture containing about 5.2 × 10⁹ mature-form parasites, a total of about 10.7 × 10⁹ merozoites were released during three consecutive harvests and about 69% of these merozoites were recovered after the isolation and purification procedures. As demonstrated by both light and electron microscopy, most merozoites were morphologically intact and the merozoite preparations were free of host cell constituents. SDS-acrylamide gel electrophoresis confirmed the absence of host cell material and also showed that merozoites had a complex protein pattern of apparent molecular weights between 225 and 15 kdaltons. Such purified merozoite preparations will be invaluable for malaria immunization studies, for identification of protective antigens of P. falciparum, and for other immunological and biochemical studies.     

The occurrence of glutamate synthase in algae.

The presence of glutamate synthase in the green algae $\text{Chlorella fusca}$ var. $\text{vacuolata}$ has been demonstrated using a whole cell assay as well as cell free extracts. The assay is complicated by the presence of glutamine (amino): α-oxoglutarate transaminase, but this enzyme can be inhibited by amino oxyacetate. The rates of glutamate synthase activity are sufficient to account for the known rates of nitrate assimilation to occur via the glutamine synthetase/glutamate synthase pathway.     

Actions of exogenous histones and other proteins on [3H]-thymidine incorporation into DNA of Novikoff hepatoma cells.

The effects of exogenous proteins on the incorporation of [3H]-thymidine into DNA was studied in Novikoff hepatoma ascites cells incubated in Eagle's minimal essential medium. A liver cytosol fraction (8 mg protein/ml) caused approximately 80% inhibition of isotope incorporation. The inhibitory activity of cytosol fractions from Morris hepatomas 9618A2, 5123C, and 20 were inversely related to their growth rate. Under conditions in which there appeared to be a density dependent inhibition of growth, a mean 10-20% stimulation of isotope incorporation was observed after addition of total calf thymus histones and individual fractions in the concentration range of 100-400 microgram/ml. In experiments with lower cell concentrations, a 60% or greater increase in [3H]-thymidine incorporation could be obtained with total calf thymus histone and with F1 and arginine-rich histones from rat liver. At concentrations of 1-2 mg/ml, histones inhibited DNA synthesis. Bovine serum albumin had little effect on DNA synthesis. Polylysine caused an 80-90% inhibition at a concentration of 1 mg/ml, but stimulatory effects were detected under certain conditions at 10 microgram/ml. The results suggest critical dependence on the ratio of cell and exogenous protein concentration in the action of proteins on DNA synthesis.     

Genetische Untersuchungen zur Inkompatibilität im Culex-pipiens-Komplex

Zusammenfassung Bei Kreuzungen zwischen Culex pipiens-Populationen verschiedener geographischer Herkunft werden drei Kreuzungstypen festgestellt: normale Kreuzbarkeit, reduzierte Kreuzbarkeit und Inkompatibilität (Nichtkreuzbarkeit). Die drei Kreuzungstypen sind mit Hilfe der Embryonierungsrate, der Schlüpfrate und der entstehenden Nachkommenschaft gegeneinander abgrenzbar. Bei Inkompatibilität sind 99.9% der sich entwickelnden Embryonen letal und etwa 0.1% der Tiere schlüpfen und sind fertile, diploide Weibchen. Die Aktivierung des Eies erfolgt durch das Spermium. Es liegt induzierte, meiotische Parthenogenese vor. Die diploiden, parthenogenetischen Weibchen gehen aus einer Oocyte 2. Ordnung oder aus Teilungsprodukten einer Oocyte 2. Ordnung hervor. Bei den letalen, haploiden Embryonen beteiligt sich das Spermium nicht am Aufbau des Embryos.

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Genetic investigations on the incompatibility in the Culex pipiens complex

Summary In crosses between populations of the mosquito Culex pipiens of different geographical origin three crossing types have been found (1) crosses with normal offspring (2) crosses with reduced offspring and (3) crosses that show almost total incompatibility. In the case of incompatible crosses 99.9% of the developing embryos are lethal and only about 0.1% of the embryos hatch and develop into fertile diploid females. The origin of the exceptional diploid females has been investigated by means of the marker genes Kuf, r, w, var, y and ru. These females develop from a diploid oocyte or from a diploid nucleus that originated by fusion of the pronucleus and the last polar body. This has been concluded from the frequency of homozygous and heterozygous offspring from heterozygous females, the frequency of equational separation of different genes and the distribution of cross-over gametes in the exceptional females. Based on the genetical data it is argued that induced meiotic parthenogenesis takes place. The sperm does not play any part in the production of the diploid females and the lethal embryos. After the activation of the egg the sperm moves to the center of the egg but it does not succeed to fuse with the pronucleus. As a result the pronucleus starts to develop into a haploid embryo in about 99.9% and only in a few cases is the diploidy restored by a change in the meiotic process in the egg.

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Teil einer Dissertation der Math.-Nat. Fakultät der Universität Mainz

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Danksagung: Herrn Prof. Dr. H. Laven danke ich für die Bereitstellung des Untersuchungsmaterials sowie für die Anregungen bei der Durchführung der Arbeit.

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Angenommen durch H. Stubbe     

Efficacy of different types of aerobic exercise in fibromyalgia syndrome: a systematic review and meta-analysis of randomised controlled trials

Introduction  

The efficacy and the optimal type and volume of aerobic exercise (AE) in fibromyalgia syndrome (FMS) are not established. We therefore assessed the efficacy of different types and volumes of AE in FMS.     

Passive restoration of vegetation and biological soil crusts following 80 years of exclusion from grazing across the Great Basin

Restoration targets for biological soil crusts are largely unknown. We surveyed seven 80‐year‐old grazing exclosures across northern Nevada for biocrusts to quantify reference conditions at relatively undisturbed sites. Exclosures were associated with the following plant communities: Wyoming big sagebrush, black sagebrush, and areas co‐dominated by winterfat and Wyoming big sagebrush. Cover of biocrusts and shrubs were generally higher than other plant groups at these sites, regardless of being inside or outside of the exclosures, suggesting these groups make up most of the native flora across the region. Important in forming soil structure, cyanobacteria of the order Oscillatoriales were less abundant and diverse in black sagebrush communities. Grazing had a negative effect on the abundance of Oscillatoriales but not the number of algal taxa, including cyanobacteria. Abundance of light algal crusts were not influenced by plant community or grazing. Dark algal crusts were generally less abundant on grazed sites. Influences of plant community and grazing were most apparent when accounting for reproductive rates of lichens and mosses based on establishment mechanisms. Abundance of shrubs, perennial grasses, Oscillatoriales, fast reproducing biocrusts and the number of algal and cyanobacterial taxa, varied by plant community, suggesting that restoration should be plant community specific. We demonstrate the affinity of rapidly reproducing biocrusts for winterfat‐Wyoming big sagebrush co‐dominated plant communities, regardless of grazing pressure. Across sites, the effects of grazing were most evident on the abundance of Oscillatoriales and slowly reproducing biocrusts following 80 years of cessation from grazing.