5-aza-C-induced changes in the time of replication of the X chromosomes of Microtus agrestis are followed by non-random reversion to a late pattern of replication

Treatment with 5-azacytidine (5-aza-C) causes an advance in the time of replication and enhances the DNase-I sensitivity of the inactive X chromosome in Gerbillus gerbillus fibroblasts. We found that these changes were not stably inherited and upon removal of the drug the cells reverted to the original state of one active and one inactive X chromosome. In order to determine whether this reversion was random, we used a cell line of female Microtus agrestis fibroblasts in which the two X chromosomes are morphologically distinguishable. In this work we show that the reversion to a late pattern of replication is not random, and the originally late replicating X chromosome is preferentially reinactivated, suggesting an imprinting-like marking of one or both X chromosomes. The changes in the replication pattern of the X chromosome were associated with changes in total DNA methylation. Double treatment of cells with 5-aza-C did not alter this pattern of euchromatin activation and reinactivation. A dramatic advance in the time of replication of the entire X linked constitutive heterochromatin (XCH) region was however, observed in the doubly treated cells. This change in the replication timing of the XCH occurred in both X chromosomes and was independent of the changes observed in the euchromatic region. These observations suggest the existence of at least two independent regulatory sites which control the timing of replication of two large chromosomal regions.Deceased on 2 Jan. 1987     

Growth curves,morphology and ultrastructure of ten Paracoccidioides brasiliensis isolates

The yeast phase of ten P. brasiliensis isolates were studied to characterize their growth pattern, morphology and ultrastructure. Growth curves were determined after counts of total and viable fungi units (FU) during 20 days. Three growth patterns were observed: slow, reaching approximately 10–30× 10⁶ FU/tube (Pb 18, Pb 265 and PB 2); intermediate, reaching 60–150×10⁶ FU/tube (IVIC Pb 9, IVIC Pb 267, Pb SN, Pb Vitor and Pb Campo Grande) and fast, reaching 180–370×10⁶ FU/tube (Pb 2052 and Pb 192). The highest percentage of viable cells occurred on the 6th day of culture for Pb 192, Pb Campo Grande, Pb 2052 and IVIC Pb 9; on the 8th day for Pb Vitor, Pb SN, Pb 18 and IVIC Pb 267; on the 10th day for Pb 265 and on the 12th day of culture for Pb 2. Mean generation times varied from approximately 21.2 (Pb 2052) to 102.6 hours (Pb 265). The isolates showed similar morphology, except IVIC Pb 267 which did not present a typical yeast-phase at 35°C and the two fast-growing isolates (Pb 2052 and Pb 192) that presented smaller cell sizes and less tendency to clump. The ultrastructure of the isolates was similar: the cell walls presented a width of 0.1 to 0.2 °; the mitochondria presented few cristae and had equivalent patterns of distribution and morphology; the endoplasmic reticulum was scanty, presenting narrow cisternae; the vacuoles, empty or filled with electrondense material, were numerous and two to five nuclei with pores were constantly observed.     

Development and Significance of Cysteamine and Propionitrile Models of Duodenal Ulcer

Cysteamine is widely used in rodents to induce duodenal ulcer. Herein, the pathogenesis of duodenal ulceration in its earliest stages was reviewed using findings from cysteamine-and propionitrile-induced duodenal ulcer in rodent models, especially taking into account changes in the secretion of gastric acid, duodenal and pancreatic bicarbonate as well asgastroduodenal motility. The effect of cysteamine-HCl in inducing ulcers in rats is circadian rhythm-dependent. The effect is greatest from just before the end of diurnal rest to just after the start of nocturnal activity. The chronobiologic effect may be in part due to the circadian rhythm-dependent increased gastric acid production from cysteamine. Titratable acidity was found to be twice as great in the gastric juice of rodents when cysteamine was given by injection at 2000 (just after the start of nocturnal activity) in comparison to when given at 0800 or 1200 (at the beginning or middle span of daily rest). Further studies have shown that adrenalectomy of rats 7 days before cysteamine administration obliterated the observed circadian susceptibility to ulcer formation. Duodenal ulceration, at least in the cysteamine model, appears to be under chronobiologic neuroendocrine control or influence, seemingly mediated by the adrenal glands.     

A catalogue of some ecuadorean fermented beverages,with notes on their microflora

Summary A catalogue of indigenous fermented beverages produced by different ethnic groups in Ecuador has been compiled and the microflora of selected examples examined. A diversity of fermentation substrates was encountered depending on the climatic zone. The fermentations are typicallyLactobacillus spp.—yeast fermentations except for one which includes a mould fermentation by a mixed starter ofMoniha sitophila, Rhizopus stolonifer and aFusarium sp. A discussion is made of the role of these beverages in the human ecology of certain regions.

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Resumen Se ha confeccionado un catálogo de bebidas indígenas ecuatorianas producidas por distintos grupos étnicos, examinándose la microflora de algunos ejemplos seleccionados. Las fermentaciones son generalmente del tipoLactobacillus sp.—levaduras, excepto en un caso que incluye una fermentación fúngica iniciada de forma mixta porM. sitophila, R. stolonifer y unFusarium sp. Se discute el papel de estas bebidas en la ecologia humana de ciertas regiones.

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Résumé Un catalogue des boissons fermentées indigènes produites par divers groupes ethniques de l'Equateur a été compilé et les micro-flores des exemples sélectionnés ont été éxaminés. Les substrats de fermentation varient d'une région climatique à l'autre. Les fermentations sont généralement du typeLactobacillus sp — levures, sauf dans un cas qui comporte une fermentation par des moisissures, avec un mélange initial deMoniha sitophila, Rhizopus stolonifer et une espèce deFusarium. Le rôle de ces boissons dans l'écologie humaine de certaines régions est discuté.

     

The role of Mg2+ in proton transport by the tonoplast pyrophosphatase in Riccia fluitans vacuoles

The Mg²⁺-dependent activity of the tonoplast pyrophosphatase (PPase) was investigated by measuring proton transport and by using the acridine orange technique on intact vacuoles of the aquatic liverwort Riccia fluitans L. In solutions with both Mg²⁺ and pyrophosphate present, a number of complexes are formed, which could all influence the enzymatic and hence the transport activity of the PPase. Therefore, the individual concentrations of these complexes were calculated and their contributions to proton transport across the tonoplast were tested. From these experiments we conclude that Mg²⁺ has three different roles: (i) Mg²⁺ stimulates transport activity of the PPase. (ii) Mg₂PP_i inhibits PPase-mediated H⁺ transport, (iii) MgPP_i* (= MgPP_i^2-+ MgHPP_i^-) is the substrate with an apparent K_1/2= 5–10 μM, with no discrimination between MgPP_i^2- and MgHPP_i^-.     

Effects of quisqualate,N-methyl-D-aspartate,and some amino acid antagonists on synaptic transmission in ampullae of Lorenzini

The effects of quisqualic acid (QA), N-methyl-D-aspartate (NMDA), and a number of NMDA and non-NMDA receptor antagonists on background and induced activity in afferent nerve fibers were investigated in skates by means of bath application to the basal membrane of electroreceptors (ampullae of Lorenzini). Perfusion with physiological saline containing QA or NMDA (minimum concentrations required: 10^–8 and 10^–5 M respectively) was found to exert an excitatory effect on afferent activity. Aminoadipate and aminophosphonobutyrate had no effect on synaptic transmission, which was blocked by aminophosphonovalerate, however. Raising magnesium ion concentration (of 30 mM) led to blockade of NMDA-induced response without changing that produced by QA. Aminophosphonovalerate blocked NMDA response and partially reduced the effects of L-aspartic acid. Glutamyl glycine produced blockade of synaptic transmission. The findings obtained would point to synaptic sensitivity to the action of amino acid agonists (QA and NMDA) in the ampullae of Lorenzini.Neurocybernetics Research Institute, Rostov-on-Don. Translated from Neirofiziologiya, Vol. 21, No. 2, pp. 160–167, March–April, 1989.     

The effect of oxidants on biomembranes and cellular metabolism

During the reductive process in the tissues, the aerobes generate a number of oxidants. Unless these oxidants are reduced, oxidative damage and cell death would occur. Oxidation of plasma membrane lipids leads to autocatalytic chain reactions which eventually alter the permeability of the cell. The role of oxidative damage in the pathophysiology of diabetic complications and ischemic reperfusion injury of myocardium, especially the changes in the channel activity which may lead to arrhythmia have been studied. Hyperglycemia activates aldose reductase which could efficiently reduce glucose to sorbitol in the presence of NADPH. Since NADPH is also aldose required by glutathione reductase for reducing oxidants, its diversion would lead to membrane lipid oxidation and permeability changes which are probably responsible for diabetic complications such as cataractogenesis, retinopathy, neuropathy etc. Antioxidants such as butylated hydroxy toluene (BHT) and also reductase inhibitors prevent or delay some of these complications. By using patch-clamp technique in isolated frog myocytes, we have shown that hydroxy radicals generated by ferrous sulfate and ascorbate as well as lipid peroxides such as t-butyl hydroperoxide facilitate the entry of Na⁺ by oxidizing Na⁺-channels. Increased intracellular Na⁺ leads to an increase in Na⁺/Ca²⁺ exchange. The increased Na⁺ concentration by itself may produce electrical disturbance which would result in arrhythmia. Increased Ca²⁺ may affect proteases and may help in the conversion of xanthine dehydrogenase to xanthine oxidase, consequently increased production of super oxide radicals. Increased membrane lipid peroxidation and other oxygen free-radical associated membrane damage in myocytes has been demonstrated.     

Hyphal fusion during initial stages of trap formation in Arthrobotrys oligospora

Hyphal fusion during initial stages of trap formation by Arthrobotrys oligospora was studied by video-enhanced contrast and electron microscopy. Trap initials grew perpendicularly to the parent hypha, then curved around and anastomosed with a peg that developed on the hypha. Trap initials usually developed 40–140 m apart while the anastomosis occurred 20–25 m from the initial. Vigorous cytoplasmic movements in trap initials and developed traps corresponded to intense staining with fluorescein diacetate (FDA) of these cells. In addition, bundles of microfilaments were seen in developing loops of traps. On fusion organelle migration took place from the tip cell of the trap into the peg. Later on a septum was formed at the site of fusion.