Molecular cloning and characterization of the mouse UDP-N-acetylglucosamine:α-3- -mannoside β-1,2-N-acetylglucosaminyltransferase I gene

The biosynthesis of protein-bound complex N-glycans in mammals requires a series of covalent modifications governed by a large number of specific glycosyltransferases and glycosidases. The addition of oligosaccharide to an asparagine residue on a nascent polypeptide chain begins in the endoplasmic reticulum. Oligosaccharide processing continues in the Golgi apparatus to produce a diversity of glycan structures. UDP-N-acetylglucosamine:α-3- -mannoside β-1,2-N-acetylglucosaminyltransferase I (EC 2.4.1.101; GlcNAc-TI) is a key enzyme in the process because it is essential for the conversion of high-mannose N-glycans to complex and hybrid N-glycans. We have isolated the mouse gene encoding GlcNAc-TI (Mgat-1) from a genomic DNA library. The mouse sequence is highly conserved with respect to the human and rabbit homologs and exists as a single protein-encoding exon. Mgat-1 was mapped to mouse Chromosome 11, closely linked to the gene encoding interleukin-3 by the analysis of multilocus interspecies backcrosses. RNA analyses of Mgat-1 expression levels revealed significant variation among normal tissues and cells.     

Nutrient transfer between the root zones of soybean and maize plants connected by a common mycorrhizal mycelium

The objective of the study was to determine whether nutrient fluxes mediated by hyphae of vesicular-arbuscular mycorrhizal (VAM) fungi between the root zones of grass and legume plants differ with the legume's mode of N nutrition. The plants, nodulating or nonnodulating isolines of soybean [ Glycine max (L.) Merr.], were grown in association with a dwarf maize ( Zea mays L.) cultivar in containers which interposed a 6-cm-wide root-free soil bridge between legume and grass container compartments. The bridge was delimited by screens (44 μm) which permitted the passage of hyphae, but not of roots and minimized non VAM interactions between the plants. All plants were colonized by the VAM fungus Glomus mosseae (Nicol. & Gerd.) Gerd. and Trappe. The effects of N input to N-sufficient soybean plants through N₂-fixation or N-fertilization on associated maize-plant growth and nutrition were compared to those of an N-deficient (nonnodulating, unfertilized) soybean control. Maize, when associated with the N-fertilized soybean, increased 19% in biomass, 67% in N content and 77% in leaf N concentration relative to the maize plants of the N-deficient association. When maize was grown with nodulated soybean, maize N content increased by 22%, biomass did not change, but P content declined by 16%. Spore production by the VAM fungus was greatest in the soils of both plants of the N-fertilized treatment. The patterns of N and P distribution, as well as those of the other essential elements, indicated that association with the N-fertilized soybean plants was more advantageous to maize than was association with the N₂-fixing ones.     

Effects of selective cholecystokinin antagonists L364,718 and L365,260 on food intake in rats

The selective type A and B cholecystokinin (CCK) receptor antagonists L364,718 and L365,260 were used to identify the receptor subtype that mediates the satiety effect of endogenous CCK. Male rats (n = 12–13/group), fed ground rat chow ad lib, received L364,718 (0, 1, 10, 100, or 1000 μg/kg IP) or L365,260 (0, 0.1, 1, 10, 100, 1000, or 10,000 μg/kg IP) 2 h after lights off, and food intake was measured 1.5, 3.5, and 5.5 h later. L364,718 significantly stimulated 1.5-h food intake by more than 40% at 10 μg/kg and higher doses; cumulative intake at 3.5 and 5.5 h remained elevated by about 20% at 1000 and 100 μg/kg of L364,718, respectively. In contrast, L365,260 had no significant stimulatory effect on feeding at any dose. The potency of L365,260 for antagonizing gastrin-stimulated gastric acid secretion was examined in unanesthetized rats. Male rats (n = 14), prepared with gastric and jugular vein cannulas, received doubling doses of gastrin (G-17I) (0.16–5 nmol/kg/h IV), each dose for 30 min, and gastric juice was collected for each 30-min period. G-17I stimulated gastric acid output dose dependently; the minimal effective dose was 0.16 nmol/kg/h, while maximal output (5-fold above basal) occurred at 5 nmol/kg/h. L365,260 (0, 1, 10, 100, 1000, or 10,000 μg/kg IV), administered 30 min before continuous infusion of G-17I (1.25 or 5 nmol/kg/h), significantly inhibited acid output only at 10,000 μg/kg; cumulative 60-min output was decreased by 60%. These results suggest that CCK acts at CCK-A receptors to produce satiety during the dark period in ad lib-feeding rats.     

The relationship between first and second chromosome segregation ratios from Drosophila melanogaster males bearing Segregation Distorter

Summary Drosophila melanogaster males heterozygous for the second chromosome locus Segregation Distorter preferentially transmit this chromosome to their progeny due to a dysfunctioning of SD ⁺-bearing sperm. SD males with a normal sex chromosome constitution produce more females than males among SD ⁺ progeny. This report shows that this unequal recovery of sexes is enhanced from XY/Y; SD/SD ⁺ males and enhanced still further from XY/O; SD/SD ⁺ males. It is argued that the probability that a SD ⁺-bearing sperm will dysfunction is related to its sex chromsome complement, with the relative probabilities of dysfunction ranked O> Y> X> XY. It is shown that a modified probit analysis accounts for the relationship between sex ratio and second chromosome segregation frequency for all paternal genotypes. Finally, SD/SD ⁺ males show no increase in sex chromosome nondisjunction with respect to a control.R. E. Denell was supported by U.S.P.H.S. Training Grant No. GM00337 and by a U.S.P.H.S. Postdoctoral Fellowship; George L. Gabor Miklos was supported by A.E.C. Contract No. AT (04-3)-34 PA150.     

Studies on the existence of a pathway in liver and muscle for the conversion of glucose into glycogen without glucose 6-phosphate as an intermediate

Mixtures of (14)C-labelled glucose plus pyruvate were incubated either with rat diaphragm or slices of rat liver. Incorporation of glucose carbon into glycogen was compared with its incorporation into glucose 6-phosphate relative to the incorporation of pyruvate carbon into these metabolic products. There was no preferential incorporation of glucose carbon relative to pyruvate carbon into glycogen compared with glucose 6-phosphate in the liver slices, but there was in diaphragm. On the assumption that glucose 6-phosphate is a necessary intermediate in the conversion of pyruvate carbon into glycogen, this is evidence for the existence in muscle, but not in liver, of more than one pool of glucose 6-phosphate or of a pathway from glucose to glycogen without glucose 6-phosphate as an intermediate. Galactose carbon, relative to pyruvate carbon, was preferentially incorporated into liver glycogen, so that a substrate converted in liver into glycogen without glucose 6-phosphate as an intermediate could be detected by this approach.     

Modulation of secretion of human chorionic gonadotropin by biologic response modifiers on term placenta and choriocarcinoma cells

The effects of biologic response modifiers such as interferon-gamma, tumor necrosis factor alpha (TNF), and retinoic acid on the human chorionic gonadotropin (hCG) secretion of cultured choriocarcinoma cells (JAR) and term placenta have been studied. Although the proliferation of JAR cells was not inhibited by these agents, retinoic acid and TNF markedly increased both the intracellular levels as well as the secreted amounts of hCG. In the case of the term placenta, only retinoic acid increased the hCG secretion into the culture medium, whereas interferon-gamma and TNF both markedly reduced secretion. The cytostatic agent etoposide (VP-16) was able to augment the hCG secretion on the choriocarcinoma cells but did not alter its production on term placenta. The The data presented indicate different mechanisms of regulation of hCG secretion in the normal and malignant trophoblast.     

Will the transgenic mouse serve as a Rosetta Stone to glycoconjugate function?

The overwhelming diversity of oligosaccharide structures on glycoproteins and glycolipids is both the most fascinating and the most frustrating aspect of glycobiology. Moreover, a single protein may be variably glycosylated and thereby represented by multiple glycoforms. As envisioned, many modifications may serve no useful function while others are likely to be essential [1]; hence, experimental approaches to understand the biological basis for such complexity can be difficult to formulate. In a recent comprehensive review on oligosaccharide function [2], Varki concludes that oligosaccharides carry out a large number of biological roles and that while all theories are correct, exceptions to each can be found. Although a common theme to oligosaccharide function may never appear, crucial biological information can be observed to reside within various glycoforms. Examples include the glycoform-dependent mechanism of selectin function in mediating haemopoietic cell extravasation during inflammatory responses [3] and the clearance of particular glycoforms from serum by various glycoform-specific receptors [4–6]. Together, studies of glycosyltransferase biochemistry, naturally-occurring and experimentally-induced glycoform mutations, and the genetic basis for the production of glycoform complexity have allowed crucial steps in the biosynthesis of specific glycan structures to be reconstructed as they appear to occur in the endoplasmic reticulum and Golgi apparatus of intact cells [7]. With a significant foundation of biochemical knowledge achieved, genetic approaches are under way further to decipher the physiological roles encoded within the diverse and dynamic mammalian oligosaccharide repertoire.     

Nutrient additions to wetlands in the Interlake region of Manitoba,Canada: effects of a single pulse addition in spring

This study examined the responses of algae and invertebrates to a single application of N and P in a series of experimental wetland enclosures in the Interlake region of Manitoba during 1989 and 1990. N and P levels in the water, sediment and vegetation were also monitored. The 3 fertilization treatments were: dissolved inorganic (6200 µg 1^–1 N, 420 µg 1^–1 P), dissolved inorganic (3200 µg 1^–1 N, 210 µg 1^–1 P) and organic (ground alfalfa meal: 6200 µg 1^–1 420 µg 1^–1 P).Dissolved nutrients in the inorganic treatments were quickly depleted from the water column, but dissolved N increased in the water column of the alfalfa treatment as the alfalfa decomposed. No changes in N or P concentrations in the sediments or vegetation were detected. Phytoplankton biomass increased in all fertilized enclosures while epiphytic periphyton exhibited only minor responses. Epipelon biomass increased in the alfalfa treatment and metaphyton standing crops were highest in the high inorganic treatments.In the alfalfa treatment, high microbial respiration rapidly reduced dissolved oxygen concentrations which negatively affected invertebrates. This trend reversed as oxygen levels increased later in the experiment. Dominant nektonic and benthic invertebrates increased in the high inorganic and alfalfa treatments. Orthocladiinae emergence increased in the high inorganic and alfalfa treatments, while Chironominae and Tanypodinae increased in the alfalfa treatment. Second year responses by algae and invertebrate communities to the fertilization treatments were minimal. Annual single pulse fertilization has the potential to increase the productivity of Interlake wetlands when nutrients are applied in the spring, however it should be noted that at the levels used in this study the effects did not extend to the second year.