Synaptonemal complexes and meiosis in myxomycetes

Synaptonemal complexes (SC) have been observed in spores 18–24 hr past cleavage in natural fruitings of Physarum cinereum, P. bogoriense, Hemitrichia stipitata, Tubifera ferruginosa, and Arcyria incarnata. Laboratory fruitings of Arcyria cinerea, Stemonitis herbatica, and a homothallic isolate of Physarum pusillum also have SC's present in spores during the same postcleavage period. The presence of these paired chromosomes of meiotic prophase in spores of species collected in nature and in a diversity of taxa suggests that the usual position of meiosis in Myxomycetes is inside the postcleavage spore. Criteria are proposed for evaluating the validity of the SC as an indicator of meiosis.     

Differential susceptibility of cultured neural cells to the human coronavirus OC43.

By using cell-type-specific markers and neural cultures derived from various areas of the nervous system, it has been possible to identify various interactions between OC43 virus and mouse oligodendrocytes, neurons, astrocytes, and fibroblasts. Neurons derived from dorsal root ganglia produced viral antigen and infectious virus. Astrocytes and fibroblasts both produced viral antigen but not infectious virus. Oligodendrocytes produced neither infectious virus nor viral antigen. Human embryo brain cells, including astrocytes, were susceptible to OC43 infection but did not produce infectious virus.     

Zinc metabolism in humans: a kinetic model

The development and testing of an integrated kinetic model describing both short and long term zinc metabolism in humans is discussed. The development took place in two stages. The first, based on a five day turnover study, details the early phases of zinc metabolism in several body tissues together with absorption and excretion. This model, however, accounts for only 10% of total body zinc. To describe the kinetics of total body zinc, a long term model which contains a reduced version of the five day model was developed. This model required an additional compartment for the liver system, but as postulated in the short term model, 90% of body zinc turns over slowly in a single compartment. The models are then used to describe the effect on zinc metabolism of different disease states and lietary perturbations. These additional studies enhance the models' validity while providing physiological insights.     

Ultrastructure of ascospore delimitation in freeze substituted samples ofAscodesmis nigricans (Pezizales)

Summary Freeze substitution proved to be a valuable technique for studying the early stages of ascosporogenesis inAscodesmis nigricans. Our observations indicate that the ascus vesicle originated from the ascus plasma membrane. Invaginations of the plasma membrane produced ascus vesicle initials consisting of two closely spaced unit membranes. The appearance of the outer leaflet of each of these membranes was identical to that of the inner leaflet of the ascus plasma membrane. Apparent points of continuity between ascus vesicle initials and the plasma membrane were observed. Ascus vesicle initials accumulated in the ascus cytoplasm near the plasma membrane and then coalesced to form the ascus vesicle, a peripheral, cylinder-like structure consisting of two closely spaced unit membranes that extended from the ascus apex to the ascus base. The ascus vesicle then became invaginated in a number of regions and subsequently gave rise to eight sheet-like segments, or ascosporedelimiting membranes, that encircled uninucleate segments of cytoplasm forming ascospore initials. Like the ascus vesicle, each ascospore-delimiting membrane consisted of two closely spaced unit membranes, the inner of which became the ascospore plasma membrane. The ascospore wall then developed between the spore plasma membrane and the outer membrane. Many details of ascospore maturation were clearly visible in freeze substituted samples.     

Fungal catabolic gene regulation: Molecular genetic analysis of theamdS gene ofAspergillus nidulans

Aspergillus nidulans is an excellent experimental organism for the study of gene regulation. Genetic and molecular analyses oftrans-acting andcis-acting mutations have revealed a complex pattern of regulation involving multiple independent controls. Expression of theamdS gene is regulated by thefacB andamdA genes which encode positively acting regulatory proteins mediating a major and a minor form of acetate induction respectively. The product of theamdR gene mediates omega amino acid induction ofamdS. The binding sites for each of these proteins have been localised throughamdS cis-acting mutations which specifically affect the interaction with the regulatory protein. The global controls of nitrogen metabolite repression and carbon catabolite repression regulate the expression of many catabolic genes, includingamdS. Nitrogen control is exerted through the positively actingareA gene product and carbon control is dependent on thecreA gene product. Each of the characterized regulatory genes encodes a DNA-binding protein which recognises particular sequences in theamdS promoter to activate or repress gene expression. In addition, there is evidence for other genetically uncharacterised proteins, including a CCAAT-binding complex, which interact with the 5 region of theamdS gene.     

Control of urea transport across toad urinary bladder by vasopressin: Effect of periodate oxidation of the mucosal cell surface

The Journal of Membrane Biology - Oxidation of toad urinary bladder epithelial cell membranes by periodate in the bathing medium altered vasopressin-stimulated transport of urea or of water and...     

Membrane transport during erythroid differentiation

Summary Transport, unidirectional flux, of a monosaccharide, a nucleoside and three amino acids, all of which enter cells by independent, discrete carriers, was compared at three stages of erythroid maturation, the normal (anucleate) mouse erythrocyte, and in differentiated and undifferentiated Friend erythroleukemia cells. We found specific transport alterations during this developmental program. Transport of 3-O-methylglucose increased with each successive developmental stage. Aminoisobutyrate transport was maintained during Friend cell differentiation, but fell slightly in erythrocytes. Leucine, lysine and uridine transport began to fall two days after dimethylsulfoxide exposure, and diminished further in red cells. These studies of transport are not directly comparable to uptake studies reported by others.Median cell volume and thus surface area decreased more during differentiation than amino acid transport declined, so flux, transport past a unit area of membrane, actually increased. Monosaccharide flux also increased. Only uridine transport fell in parallel to surface area. Perhaps sites for nutrient transport required for energy production are preferentially maintained.     

Primary structure of an unusual glycine tRNA UGA suppressor.

We have determined the nucleotide sequences of two UGA-suppressing glycine transfer RNAs. The suppressor tRNAs were previously shown to translate both UGA and UGG and to have arisen as a consequence of mutation in glyT, the gene for the GGA/G-reading glycine tRNA of Escherichia coli. In each mutant tRNA, the primary sequence change was the substitution of adenine for cytosine in the 3' position of the anticodon. In addition, a portion of mutant glyT tRNA molecules contained N6-(delta 2-isopentenyl)-2-thiomethyl adenine adjacent to the 3' end of the anticodon (nucleotide 37). The presence or absence of this hypermodification may be a determinant in some of the biological properties of the mutant tRNA.     

AN ULTRASTRUCTURAL STUDY OF SPERMATIUM FORMATION IN THE RUST FUNGUS GYMNOSPORANGIUM JUNIPERI-VIRGINIANAE

Spermatium formation in G. juniperi-virginianae is phialidic. The spermatia are blown out of the tips of spermatiophores which possess a thickened neck region and a distinct, flared collarette. Each spermatium initial is surrounded by a thin wall which is attached to the inner surface of the spermatiophore wall just below the thickened neck region. A spermatium is delimited by a centripetally developing septum and then pushed into the spermogonial cavity by the next spermatium initial. Mature spermatia are ellipsoid with tapered ends and are surrounded by a thin wall. Each contains a single nucleus, many ribosomes, a few small vacuoles, and a number of lipid bodies and mitochondria.