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1.
Synaptonemal complexes and meiosis in myxomycetes 总被引:4,自引:0,他引:4
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. 相似文献
2.
Differential susceptibility of cultured neural cells to the human coronavirus OC43. 总被引:2,自引:2,他引:0 下载免费PDF全文
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. 相似文献
3.
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. 相似文献
4.
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. 相似文献
5.
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... 相似文献
6.
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. 相似文献
7.
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. 相似文献
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9.
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. 相似文献
10.
Anti-phospholipase A2 receptor autoantibody (PLA2R-Ab) plays a critical role in the pathogenesis of primary membranous nephropathy (PMN), an autoimmune kidney disease characterized by immune deposits in the glomerular subepithelial spaces and proteinuria. However, the mechanism of how PLA2R-Abs interact with the conformational epitope(s) of PLA2R has remained elusive. PLA2R is a single transmembrane helix receptor containing ten extracellular domains that begin with a CysR domain followed by a FnII and eight CTLD domains. Here, we examined the interactions of PLA2R-Ab with the full PLA2R protein, N-terminal domain truncations, and C-terminal domain deletions under either denaturing or physiological conditions. Our data demonstrate that the PLA2R-Abs against the dominant epitope (the N-terminal CysR-CTLD1 triple domain) possess weak cross-reactivities to the C-terminal domains beyond CTLD1. Moreover, both the CysR and CTLD1 domains are required to form a conformational epitope for PLA2R-Ab interaction, with FnII serving as a linker domain. Upon close examination, we also observed that patients with newly diagnosed PMN carry two populations of PLA2R-Abs in sera that react to the denatured CysR-CTLD3 (the PLA2R-Ab1) and denatured CysR-CTLD1 (the PLA2R-Ab2) domain complexes on Western blots, respectively. Furthermore, the PLA2R-Ab1 appeared at an earlier time point than PLA2R-Ab2 in patients, whereas the increased levels of PLA2R-Ab2 coincided with the worsening of proteinuria. In summary, our data support that an integrated folding of the three PLA2R N-terminal domains, CysR, FnII, and CTLD1, is a prerequisite to forming the PLA2R conformational epitope and that the dominant epitope-reactive PLA2R-Ab2 plays a critical role in PMN clinical progression. 相似文献