Antitumour activities of levans produced by Zymomonas mobilis strains

Levans produced by four Zymomonas mobilis strains showed antitumour activity against sarcoma 180 and Ehrlich carcinoma in Swiss albino mice. Levans from two strains (ZAP and CP4) had the highest effects. NMR analysis showed that the polymers were composed only of fructose units. The results suggested that the antineoplasic effect is associated to the polysaccharide molecular weight and that a particular molecular weight range may be responsible for this effect.     

Swelling of golgi apparatus cisternae in monensin-treated tissues is modulated by fixation conditions

Summary Swelling of Golgi apparatus cisternae is reported to be a common response to the ionophore, monensin. However, the amount of swelling depends on fixation, thus raising the question of whether the swelling response is due to monensin or to the fixation protocol. To resolve this problem, maize root cap cells were treated with monensin and then fixed with glutaraldehyde and osmium tetroxide (applied sequentially), osmium tetroxide alone, or aqueous potassium permanganate, or were quick frozen in liquid propane and substituted in acetone-osmium tetroxide. The chemical fixatives (which take minutes to stabilize tissue elements) were judged by comparison with freeze substitution which requires only fractions of a second to stabilize tissue elements. The results verify that monensin causes cisternal swelling and that this swelling is best observed at the ultrastructural level by fixation in glutaraldehyde/osmium tetroxide or by freeze substitution.     

Variation in the ribosomal internal transcribed spacers (ITS1 and ITS2) among eight taxa of the Mimulus guttatus species complex

The internal transcribed spacer region (ITS1 and ITS2) of the 18S-25S nuclear ribosomal DNA sequence and the intervening 5.8S region were sequenced from three individuals in each of eight taxa of the Mimulus guttatus species complex. Three discrete variants, or "types," of ITS sequences were found, among which 30%-40% of sites differed, compared with 1%-2% within types. Dot plots indicate that these types were not related by conspicuous rearrangements or inversions. More than one ITS type was often found in the same taxon, and two of three ITS types span species boundaries, indicating their presence prior to speciation. These ITS sequences showed essentially no positional homology with the nearest sequenced relative, tomato. In contrast, the 5.8S region was relatively unvaried, with 8 of 162 sites varied in the sample among all eight taxa. The phylogeny inferred by the most common ITS sequence type, rooted by the two other ITS types, agreed with isozymes in showing the distinctness of M. nudatus, M. laciniatus, and M. tilingii from the other five taxa.      

Satellite Spitzenkörper in growing hyphal tips

Summary Growing hyphal tips of higher fungi contain an organized assemblage of secretory vesicles and other cell components collectively known as the Spitzenkörper. Until now, the Spitzenkörper has been portrayed as a single spheroid complex located near the apical cell wall. This study demonstrates the occurrence of multiple Spitzenkörper in growing hyphal apices imaged by video-enhanced phase-contrast microscopy. In addition to the main Spitzenkörper, smaller satellite Spitzenkörper arise a few micrometers behind the apical pole. Four developmental stages were identified: (a) the satellites first appeared as faint phase-dark plaques next to the plasma membrane, (b) gradually increased in size and assumed an ovoid profile, (c) they migrated to the hyphal apex, and (d) finally they merged with the main Spitzenkörper. After the merger, the main Spitzenkörper temporarily increased in size. Satellites were observed in 14 fungi, most of which had relatively large (5–10 m diam.), fast-growing hyphae (2–33 m/min elongation rate). The average frequency of in-focus satellites was 7+/min forFusarium culmorum and 11+/min forTrichoderma viride. As with the main Spitzenkörper, satellites were present only in growing cells. They were transient and remained visible for 3–8 s before merging with the main Spitzenkörper. Within the hyphae, satellites travelled up to six times faster than the average cell elongation rate. Multiple satellites sometimes occurred simultaneously; up to three were seen within a hyphal apex at the same time. Localized cell enlargement occurred next to stationary satellites, suggesting that satellite Spitzenkörper are functional as sources of new cell surface before they reach the main Spitzenkörper; therefore, they account for some variations in the profiles of the growing hyphae. By electron microscopy, satellites consisted of small clusters of apical vesicles surrounding a group of microvesicles located next to the plasma membrane. The identification and behavior of the satellites represent clear evidence of directional mass transport of vesicles toward the hyphal apex. Our observations indicate that satellites are a common phenomenon in growing hyphal apices of septate fungi and that they contribute to growth of the hyphal apex.Abbreviations VSC vesicle supply center     

Variation in heat shock proteins within tropical and desert species of poeciliid fishes

The 70-kilodalton heat shock protein (hsp70) family of molecular chaperones, which contains both stress-inducible and normally abundant constitutive members, is highly conserved across distantly related taxa. Analysis of this protein family in individuals from an outbred population of tropical topminnows, Poeciliopsis gracilis, showed that while constitutive hsp70 family members showed no variation in protein isoforms, inducibly synthesized hsp70 was polymorphic. Several species of Poeciliopsis adapted to desert environments exhibited lower levels of inducible hsp70 polymorphism than the tropical species, but constitutive forms were identical to those in P. gracilis, as they were in the confamilial species Gambusia affinis. These differences suggest that inducible and constitutive members of this family are under different evolutionary constraints and may indicate differences in their function within the cell. Also, northern desert species of Poeciliopsis synthesize a subset of the inducible hsp70 isoforms seen in tropical species. This distribution supports the theory that ancestral tropical fish migrated northward and colonized desert streams; the subsequent decrease in variation of inducible hsp70 may have been due to genetic drift or a consequence of adaptation to the desert environment. Higher levels of variability were found when the 30- kilodalton heat shock protein (hsp30) family was analyzed within different strains of two desert species of Poeciliopsis and also in wild-caught individuals of Gambusia affinis. In both cases the distribution of hsp30 isoform diversity was similar to that seen previously with allozyme polymorphisms.      

Sedimentation properties of chitosomes fromMucor rouxii

Summary This study was undertaken to assess the distribution and localization of chitin synthetase in a fungal cell and to evaluate the sedimentation behavior of chitosomes (microvesicular containers of chitin synthetase). Chitosomes were isolated from cell-free extracts of yeast cells ofMucor rouxii by rate-zonal and isopycnic sedimentation in sucrose density gradients. Because of their small size and low density, chitosomes were effectively separated from other subcellular particles. Rate-zonal sedimentation was a suitable final step for isolating chitosomes as long as ribosomes had been eliminated by enzymic digestion. By isopycnic centrifugation, chitosomes could be separated directly from a crude cell-free extract; they cosedimented with a sharp symmetrical peak of chitin synthetase at a buoyant density of d=1.14–1.15g/cm³; the only significant contaminants were particles of fatty acid synthetase complex. From such sedimentations, we estimated that 80–85% of the chitin synthetase activity in the cell-free extract was associated with chitosomes; the rest was found in two smaller peaks sedimenting at d=1.19–1.20 and d=1.21–1.22 (5–10%), and in the cell wall fraction (5–10%). By consecutive rate-zonal and isopycnic sedimentations, chitosome preparations with relatively few contaminating particles were obtained. Potassium/sodium phosphate buffer (pH 6.5)+MgCl₂ was the most effective isolation medium for chitosomes. Other buffers such as TRIS-MES+MgCl₂ led to massive aggregation of chitosomes and a change in sedimentation properties. This tendency of chitosomes to aggregate could explain why most of the chitin synthetase activity of a fungus is sometimes found associated with other subcellular structures,e.g., plasma membrane.     

Ultrastructural alteration of plant plasma membranes induced by auxin and calcium ions

Ultrastructural changes in isolated and in situ plasma membranes of etiolated soybean hypocotyls (Glycine max L. cv. Wayne) were induced by indole-3-acetic acid (IAA), other auxins, and calcium chloride. Fixed and embedded preparations were stained by a phosphotungstate-chromate procedure to identify and accentuate plasma membrane. Measurements were on micrographs obtained with an electron optical system calibrated and corrected for reproducible and accurate size measurements. Plasma membranes treated for 20 minutes with 1 mum IAA were 10 to 15% thinner than controls. The response to IAA was rapid, reproducible, auxin-specific, temperature-dependent, and reversible. Comparable responses were obtained with isolated and in situ membranes. Membranes treated with 0.5 m calcium chloride for 20 minutes were 15 to 20% thicker than controls. Multiple cycles of alternating calcium and IAA treatments yielded membranes with dimensions that reflected the last treatment of the series. The findings show a direct response of plasma membranes to growth regulating agents and provide evidence for a cell-free response of isolated plasma membranes to a hormone.     

MS-275, a potent orally available inhibitor of histone deacetylases--the development of an anticancer agent

In the last few years it was found that beside genetic aberrations, epigenetic changes also play an important role in tumorigenesis. Acetylation and deacetylation of histones have been found to contribute to a significant extent to epigenetic regulation of gene expression. Analyses of various tumor models and patient samples revealed that the enzyme class of histone deacetylases is associated with many types of cancer and that, for example, over-expression of these enzymes leads to a disturbed balance between acetylation and deacetylation of histones, resulting in differences in the gene expression patterns between normal and cancer cells. Consequently, this class of enzymes has been considered as a potential target for cancer therapy. Numerous inhibitors have been identified and several are in clinical development. Although, with SAHA, one inhibitor has been approved by the FDA for a tumor indication, many open questions remain regarding the mode of action of these inhibitors. In this review, various aspects of preclinical and clinical research of the HDAC inhibitor MS-275 are described, to provide insight into the development of such a compound.     

柠檬酸合酶的分子生物学研究进展

柠檬酸合酶（citrate synthase,CS）是细胞内多种重要代谢途径的关键酶。CS可催化草酰乙酸和乙酰辅酶A之间的缩合反应生成柠檬酸和辅酶A。通常革兰氏阳性细菌、古菌以及真核细胞的CS为同源二聚体,而革兰氏阴性细菌的CS为同源六聚体。根据其在细胞内的定位不同,CS可分为线粒体CS、乙醛酸循环体CS、过氧化物酶体CS。这些同工酶在能量代谢、植物脂肪的代谢、脂肪酸的氧化及细胞解毒过程中起着重要作用。不同来源的CS空间结构、催化机制和动力学性质十分相似。针对其生化特性、空间结构特点、催化机制以及分子进化等研究进展进行综述。     

Effects of long-term fixation on histological quality of undecalcified murine bones embedded in methylmethacrylate

While long-term fixation and storage of specimens is common and useful for many research projects, it is particularly important for space flight investigations where samples may not be returned to Earth for several months (International Space Station) or years (manned mission to Mars). We examined two critical challenges of space flight experimentation: the effect of long-term fixation on the quality of mouse bone preservation and the preservation of antigens and enzymes for both histochemical and immunohistochemical analyses, and how the animal/sample processing affects the preservation. We show that long-term fixation minimally affects standard histological staining, but that enzyme histochemistry and immunolabeling are greatly compromised. Further, we demonstrate that whole animal preservation is not as suitable as whole leg or stripped leg preservation for long-term fixation and all histological analyses. Overall, we recommend whole leg processing for long-term storage of bone specimens in fixative prior to embedding in plastic for histological examination.