Characterization of human chromosomal unit fibers

A structural component of mitotic chromosomes that partially explains the compaction of DNA within mitotic chromosomes is suggested on the basis of the occurrence of long, regular cylindrical structures in preparations of isolated human chromosomes. These structures, unit fibers, of a rather constant diameter of about 4,000 Å have been postulated to be formed by coiling of the 250T2–300 Å solenoid chromatin fiber that itself is formed by coiling of the 100 Å string of nucleosome fiber. The human chromatid would thus be composed by a hierarchy of helices with contraction ratios for DNA at each level of coiling of 7 (string of nucleosomes), 5 (solenoid) and 40 (4,000 Å unit fiber or super-solenoid) which results in an overall contraction ratio for DNA in the unit fiber structures of about 1,400, which is approximately 5-fold less than the final contraction of DNA in intact chromatids of condensed metaphase chromosomes. The present report concerns more detailed studies with respect to the dimensions and cytochemical properties of the unit fiber structures observed in preparations of isolated human mitotic chromosomes that provide direct and indirect evidence in support of their super-solenoid structure and relate to known properties of human mitotic chromosomes.     

Effects in vitro of alloxan on the glucose metabolism of mouse pancreatic B-cells

To facilitate detailed studies of the B-cytotoxic action of alloxan we developed a model using isolated pancreatic islets of normal mice. An essential feature of this model is the low temperature employed during exposure to alloxan, which minimizes the degradation of the drug. The islets were incubated with alloxan for 30min at 4 degrees C and subsequently various aspects of their metabolism were studied. The O(2) consumption was measured by the Cartesian-diver technique. Islets exposed to 2mm-alloxan and control islets had the same endogenous respiration, whereas the O(2) uptake of the alloxan-treated islets was inhibited and that of the control islets stimulated when they were incubated with 28mm-glucose as an exogenous substrate. The islet glucose oxidation was estimated by measurement of the formation of (14)CO(2) from [U-(14)C]glucose at 37 degrees C. Compared with the controls, alloxan-treated islets showed a decrease in the glucose-oxidation rate in a dose-dependent manner. Pretreatment of the islets with 28mm-glucose for 30min at 37 degrees C completely protected against this effect, whereas preincubations at glucose concentrations below 16.7mm failed to exert any protective effect. The glucose utilization was estimated as the formation of (3)H(2)O from [5-(3)H]glucose. Alloxan (2mm) failed to affect islet glucoseutilization rate in the presence of either 2.8 or 28mm-glucose. In contrast, islets exposed to 5 or 10mm-alloxan exhibited lowered glucose utilization. It is concluded that in vitro alloxan has an acute inhibitory effect on the islet glucose metabolism, and that this action can be prevented by previous exposure to a high glucose concentration. The results are consistent with the idea that the B-cytotoxicity of alloxan reflects an interaction with intracellular sites involved in the oxidative metabolism of the B-cell.     

Heavy metal tolerance of marine phytoplankton. III. Combined effects of copper and zinc ions on cultures of four common species

The combined effects of copper and zinc ions on the growth of three marine diatoms and one dinoflagellate in culture have been studied. The two metals were found to act synergistically to all algae except Phaeodactylum tricornutum Bohlin. With this species an antagonistic effect was observed. Addition of zinc ions reduced the inhibition of growth caused by the more toxic copper ions. Zinc toxicity to this alga increased at low concentration of magnesium, indicating a common route for divalent metal ions in general.     

Autoradiographic study on the localization of estradiol-17β in neonatal mouse uterus and cervix

Summary The uptake of ³H-estradiol-17 in the neonatal mouse uterus and cervix has been studied by an autoradiographic method. When the radio-active hormone is administered in vivo and in vitro, grains are found to be concentrated above the nuclei both in the uterine and cervical epithelium and stroma. Grain counts revealed that the nuclear concentration of grains is higher at 4 h than at 2 h after isotope injection. The cervical epithelium has a higher nuclear concentration than the uterine epithelium both in vivo and in vitro. In the stroma, this situation is reversed except after in vitro treatment of the tissues.In the cervix, more of the hormone seems to be located within the nucleus while in the uterus a higher proportion of the grains are found in the vicinity of the nuclear periphery.Although the nuclear concentration of grains is higher at 4 h than at 2 h, the number of grains above the sections is lower at 4 h. Both in vivo and in vitro, the number of grains is higher above the stromal than above the epithelial compartments of the uterus and cervix.Five days old animals showed the same labeling pattern. The differences in uptake and distribution of ³H-estradiol are discussed in relation to other known differences in the hormone responsiveness in these tissues.We are greatly indebted to Professor W.E. Stumpf and the Laboratories for Reproductive Biology, University of North Carolina Medical School for the opportunity to study the method of dry mount autoradiography. The work has been supported by the Norwegian Research Council for Science and the Humanities and by the Norwegian Cancer Society (Landsforeningen mot Kreft)     

Food‐web structure and mercury dynamics in a large subarctic lake following multiple species introductions

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Elevation of the Extracellular Concentrations of Glutamate and Aspartate in Rat Hippocampus During Transient Cerebral Ischemia Monitored by Intracerebral Microdialysis

Rats were implanted with 0.3-mm-diameter dialysis tubing through the hippocampus and subsequently perfused with Ringer's solution at a flow rate of 2 microliter/min. Samples of the perfusate representing the extracellular fluid were collected over 5-min periods and subsequently analyzed for contents of the amino acids glutamate, aspartate, glutamine, taurine, alanine, and serine. Samples were collected before, during, and after a 10-min period of transient complete cerebral ischemia. The extracellular contents of glutamate and aspartate were increased, respectively, eight- and threefold during the ischemic period; the taurine concentration also was increased 2.6-fold. During the same period the extracellular content of glutamine was significantly decreased (to 68% of the control value), whereas the concentrations of alanine and serine did not change significantly during the ischemic period. The concentrations of gamma-aminobutyric acid (GABA) were too low to be measured reliably. It is suggested that the large increase in the content of extracellular glutamate and aspartate in the hippocampus induced by the ischemia may be one of the causal factors in the damage to certain neurons observed after ischemia.     

Molecular phylogenetics of the tribeInuleae s. str.(Asteraceae), based on ITS sequences of nuclear ribosomal DNA

The sequences of the internal transcribed spacer (ITS) region of 18S–26S nrDNA for a sample of 16 taxa from theInuleae s. str. and two outgroup taxa are analysed cladistically with PAUP. A consensus tree of the four most parsimonious cladograms is presented. Three different tests of cladogram stability are conducted (Bremer support, parsimony jackknifing and bootstrapping); all tests indicate a high degree of support for the basal nodes of the tree. The ITS phylogeny of the tribe is compared with previous hypotheses based on morphological data. The position ofAnisopappus as sister group to the rest of the tribe is supported by the molecular data, but the proposed subdivision ofInuleae s. str. into a paleate grade group and an epaleate clade is not. The interpretation of the character evolution of, e.g. receptacular paleae and pappus features within the tribe is discussed.     

Climate change at northern latitudes: rising atmospheric humidity decreases transpiration, N-uptake and growth rate of hybrid aspen

At northern latitudes a rise in atmospheric humidity and precipitation is predicted as a consequence of global climate change. We studied several growth and functional traits of hybrid aspen (Populus tremula L.×P. tremuloides Michx.) in response to elevated atmospheric humidity (on average 7% over the ambient level) in a free air experimental facility during three growing seasons (2008-2010) in Estonia, which represents northern temperate climate (boreo-nemoral zone). Data were collected from three humidified (H) and three control (C) plots, and analysed using nested linear models. Elevated air humidity significantly reduced height, stem diameter and stem volume increments and transpiration of the trees whereas these effects remained highly significant also after considering the side effects from soil-related confounders within the 2.7 ha study area. Tree leaves were smaller, lighter and had lower leaf mass per area (LMA) in H plots. The magnitude and significance of the humidity treatment effect - inhibition of above-ground growth rate - was more pronounced in larger trees. The lower growth rate in the humidified plots can be partly explained by a decrease in transpiration-driven mass flow of NO(3) (-) in soil, resulting in a significant reduction in the measured uptake of N to foliage in the H plots. The results suggest that the potential growth improvement of fast-growing trees like aspens, due to increasing temperature and atmospheric CO(2) concentration, might be smaller than expected at high latitudes if a rise in atmospheric humidity simultaneously takes place.     

Carbohydrate degradation and methane production during fermentation ofLaminaria saccharina (Laminariales,Phaeophyceae)

Anaerobic digestion of the brown algaLaminaria saccharina (L.) Lamour. harvested in spring and autumn was carried out at controlled laboratory conditions in stirred fermentor systems. Due to the normal seasonal variations, the autumn material had a much higher content of carbohydrates such as mannitol and laminaran. Both batch and semi-continuous feeding conditions were investigated for periods up to 800 h, with inoculum provided from previous kelp fermentations. In batch cultures, the methane yield from the autumn material was doubled compared to that of the spring material. Semi-continuous conditions gave more similar methane yields for both raw materials, 0.22 and 0.27 l CH₄ per g VS for spring and autumn material, respectively. In all experiments, mannitol and laminaran were reduced to less than 5 of the initial values within 24–48 hours after inoculation, whereas 30 of the alginate content was detectable even after 30 days. Viscometry revealed that this material was severely depolymerized, and alginate lyase activity was found to develop rapidly in all cultures. Although mannitol and laminaran were fermented much faster than alginate, the total accumulated methane yields seemed to be determined by the total carbohydrate content of the raw material during extended semi-continuous feeding.(*author for correspondence)     

Evidence that Aspartate Aminotransferase Activity and Ketodicarboxylate Carrier Function Are Essential for Biosynthesis of Transmitter Glutamate

Based on the selective inhibition of glutamate release in cerebellar granule cells in primary cultures by the aspartate aminotransferase inhibitor, aminooxyacetic acid, and by the ketodicarboxylate carrier inhibitor, phenylsuccinate, a novel model for synthesis of transmitter glutamate is suggested: Glutamate is formed from glutamine in the mitochondrial intramembrane space by phosphate-activated glutaminase, transported across the inner membrane in exchange with aspartate, transaminated in the matrix to alpha-ketoglutarate, which via the ketodicarboxylate carrier is transferred to the cytoplasm, and transaminated to form transmitter glutamate. Such a mechanism would explain the functional role of aspartate aminotransferase in glutamatergic neurons.